Trouble diagnosing overheating M50
!994 525it overheated and I am in need of some help in diagnostic. My son overheated the car and said the needle did not go to red. He added coolant but was unable to bleed it properly. I got a look at it today. The oil is very clean. The fan clutch seems fine. I filled the expansion tank until coolant flowed from the bleed valve and started the car. It stared well and ran smooth. Fan started immediately. Temperature needle just past blue and top hose gets warm. Idle for 15 minutes and needle steady at 1/2 mark. Turn heat on full with blower and begin to bleed. Coolant with bubbles for a few minutes and then steam but not heat in cabin. Turn off engine, fill expansion until flow out of bleed valve and repeat with same result as before..bubble then steam. This is repeated for an hour with same result and needle steady at 1/2 mark. There is some white steam out of exhaust but here always has been. I began to raise the rpms to 2000 after the pure steam began coming out of the bleed valve and would get more coolant and bubbles. I disconnected the top radiator hose because it seemed soft and empty. I did get flow but the hose did not seem "full". I do not know what it should look like. Less exhaust vapor now but still some at idle. Not heat in cabin. Have been bleeding for at least 1 1/2 hours by now. Took car for a drive. The temp gage fluctuates slightly between 1/2 and 2/3 and always comes back to 1/2 at idle. Begin bleed procedure again. The expansion tank losses very little coolant each time but after a few minutes of coolant and bubbles (escaping fast then slower with a slight pulsation and then steam endlessly) I again disconnect top hose and manually fill with coolant, it takes a quart or more. I am still not getting cabin heat so I begin to disconnect the heater hoses and there is hot coolant. For the first time I am getting some heat in the cabin but only from the driver side vent. All three heater hoses are hot. There is a fourth which enters the fire wall next to the three and goes under the intake manifold and this one is not as hot. I loosen the clamp and see coolant flow. I am encouraged. I take the car for another drive and it seems to run fine. The temp gauge is steady at 1/2. There is some heat on the driver side and I notice that when I get the rpms up as high as I can between red lights that there is a surge of hot air as I decelerated to idle but it does not last that long. The needle is steady at 1/2 and is so steady that I am fearing that the gauge is broken. I return and there is no water vapor visible at exhaust. I cover the exhaust with a clothe and detect moisture. I start my truck and compare. My truck (F-150) blows some vapor but not as much as the BMW and stops sooner. I check exhaust with a clothe and there is also moisture but the truck exhaust feels hotter. The cabin heat is intermitten and never is warm on the passenger side. I bleed again and again but it never stops steaming out of the bleed valve. My son drives to the grocery store and I follow him, all seems well. He calls me after he gets home to say that the car began to overheat just before he got home. A 6 mile round trip. The car engine probably ran for at least 4 hours either at idle, at 2000 prm or on a few short drives before it finally overheated. THe radiator looks very good and I could spot no leaks. I do not know what is acceptable amount of water vapor. I have read a few threads on the subject with no real conclusion. I think I may need to get a pressure test. There is a noise from the upper front of the engine which sounds like valves tapping. I do not think it is new since the overheating and it may have been there all along. Any helpful suggestions would be appreciated. Is there a definitive test for the water pump? The thermostat appears to be opening but the flow may be low. I just do not know. It seems like the emphasis on bleeding air out of the system is so great that I would think that the top radiator hose would be solidly full of coolant but it feels soft and empty. I do not what is normal. Thanks for any help.
not paragraphed, did not read
I did read your instructive post but did not see anything on sentence structure. Sorry, I will break it up differently next time. I was trying to give a chronological sequence of events thinking that would be the best information.
I did research the "ticking" noise and it may be a loose spark plug, loose belt, loose pulley, lifter or a water pump going bad. Shall I rewrite the post of leave it as is?
Yes, please edit your original post and follow the usual rules of paragraphing if not it will be such a pain to read. Try to read it back yourself and you'll understand what I mean.
I went in 4 lines and stopped. I can tell you one thing. You're not supposed to get steam coming out of your bleed screw/bleed valve area, after the screw has been tightened down. There's your problem right there. I suggest you change the bleed screw. Before you do that, please remove it and take a good look at the threads that the screw goes into. Inspect it for cracks and anything else that might be obviously wrong.
The bleed screw is a cheap thing to purchase. Like $2 or less.
You don't need to bleed your radiator more than once. Its simple, and if it doesn't work with this then you have other issues. With the rad cap and bleed screw off, start the engine and bring it to operating temperature. Don't bleed it when its cold. Turn on the cabin heater to full heat and full blast (if your cabin heater works that is). Bleed the radiator in the usual way and replace the bleed screw once the bubbles stop. Top up to full on the expansion tank and fix the rad cap back firmly.
DO NOT remove the radiator hoses etc after that to fill up coolant (doing so to check other stuff is fine). Whenever hoses are removed, air is introduced into the system. You'll need to bleed the radiator all over again.
Just read your last 3 lines. When you are at operating temperature, the top hose should feel hot. It should not feel empty but it doesn't necessarily feel "full" either. You should be able to squeeze it somewhat.
Please check your dipstick and under your oil cap. If you've got any milkyness, then water is mixing with your engine oil, and that's how you're losing coolant. That indicates a head gasket problem or worse.
It is not good that you've got too much moisture coming out of your tailpipe. The amount that you feel out of your truck's exhaust should be about the same as on your car.
Try not to drive this car much.
If you reply to these posts, please use proper paragraphing if not we will not follow. Thanks.
The bleed screw if fine. The steam comes out only when the screw is loose. I bled the system with the expansion tank cap on and tight. Are you saying to leave the Radiator cap off and the bleed screw completely out during bleeding?
Fill up the expansion tank, and bubbles will come out of the bleed screw's hole. When it stops, replace the bleed screw, top up your expansion tank to maximum, then afix the rad cap back securely.
Do this with the engine at operating temperature.
Thanks, that may be my problem. I had the Rad cap on tight as I had read how important it was to have the system under pressure. Bentley is ambiguous and other sites had said to tighten cap. I will try again in the morning.
Very little coolant was lost from the expansion tank and steam would escape from the bleed screw. Was the rad cap on preventing the flow of coolant to the bleed screw? I also thought that the coolant would pour out of the expansion tank since it is under pressure.
The oil is clean mobil 1 synthetic. But the head gasket can still be bad, right? Will the coolant circulate with a bad water pump as long as the thermostat is open?
Also I have read in many threads that white vapor is quite normal for the m50 engine, is that true?
Is it important to raise the front of the car during bleeding?
Why would only the driver side heat get hot?
You are not supposed to bleed anything under pressure. You've clearly misread something.
I once encountered a diagram of our radiator. The expansion tank connects to the radiator with a passage for water to flow back and forth between both depending on conditions. The bleed screw is located at the top of one of the main radiator passages.
Please follow my instructions to the letter. Do not improvise, at least for now.
1. Bleeding the radiator is a simple thing. If you're having trouble with it, or if you read instructions anywhere that make it sound complicated, you or they are doing it wrong. This is very important for you to internalise and use as a guide...as you need to unlearn alot of wrong stuff you've picked up over the years. Too many people over here seem to have problems with something that I find so simple. This is irritating because I initially tried just about all the unnecessary ideas I read about here (such as parking the car on an incline etc) to make sure my radiator was purged of bubbles, before realising after many months that it doesn't matter.
1. Remove the rad cap and bleed screw.
2. Fill up water/coolant in the expansion tank until water runs from the bleed screw. If bubbles run out, keep filling water until they stop.
3. Start the engine.
4. Activate max heat and max blower on your cabin heater, if it is working even partially. If it does not work at all, you can ignore this.
5. Wait till the engine reaches operating temperature. Do not rev the engine at this time, coolant will spill everywhere.
6. When it reaches operating temperature and you've got cabin heat (should take around 10 minutes or less), fill up more coolant into the expansion tank. Water will run out the bleed screw, along with any bubbles.
7.1 When bubbles stop running out and you've only got coolant, fix the bleed screw back....while the coolant is running out of the bleed screw. You will be able to do this somewhat by hand and then you can tighten it with a screwdriver etc. If you don't time this perfectly, don't worry. Air doesn't get sucked in, and even if it does its not much and won't matter to the engine.
7.2 This will not take longer than 5 minutes after your engine has reached operating temperature. If you need more time for this then 5 minutes.....come and rebleed the radiator 2 days later after driving. If, during rebleeding you notice alot of bubbles,...then rebleed 2 days later again after more driving. If you notice alot of bubbles still, you might have a problem with your engine. NOTE : if you notice a few bubbles each time you bleed, this is normal.
8. Fill up the expansion tank to the brim, then tighten down the rad cap on top of that. Some coolant may spill, its ok. Don't worry about compressing coolant etc. Never happened.
9. Coolant levels will adjust and come down during driving over the next 2 months. This is normal. Open your rad cap and top up with water at least once every 2 months. To make it easier to remember, just top up water once every month instead.
10. Get a new rad cap and a new bleed screw. Always better to be safe than sorry, and these things are cheap...like under $15 for both together. Keep the old bleed screw as a spare.
If coolant levels drop so fast that you need to top up water once a week, you've got a problem somewhere. The pressure test with the radiator would be something you'll need to do to check it out. If that's ok, then you'll need to look for leaks and trace faults to the engine.
Its always a good idea to use cheap, brightly coloured, and strong smelling coolant that is sold at walmart. The OEM coolant is too expensive and too light blue...it will be hard to isolate leaks if they occur....and because it doesn't have a strong smell, if any coolant hose ruptures, you won't get a warning through a strong coolant smell invading the cabin. This happens far more quickly than a red line on your temp gauge, and so gives you more time to stop the engine and react to things.
For good measure, please check your auxiliary fan's fuses in the fuse box to make sure that your aux fan is working fine. It has a secondary cooling function along with the fan clutch. In fact, I've just removed the fan clutch from my car and am fully cooled by the aux fan and its coolant temperature sensor alone. The car drives better and there's alot more space in the engine bay to see stuff. :)
B. With a bad water pump, coolant will either barely circulate or not circulate at all. In both scenarios, overheating would result fairly quickly. One simple and by no means comprehensive way to check if your wp is ok is to grab one of the fan clutch's blades and pull it upwards and forwards and backwards. I.e. check if there is free play. If there is, then you might have impending issues. This by itself is by no means conclusive.
C. White vapour out the tailpipe is not normal for the M50 except for exceptionally wet days, in which case every car's tailpipe should show some vapour. Please don't believe everything that you read on the internet. (Just had to say that lolol).
D. No you don't have to raise the front of the car during bleeding. Another myth created by someone who is hoping that his car's overheating was due to incomplete bleeding and not something else that he'd rather not have.
If someone did this and it worked, then it was by accident; in the process of doing this, that person would have done something else right that he had been missing all this while. It happens to the best of us.
E. If you've got heat coming in on only one side of your cabin, it is possible that one of your heater valves (there are two) is stuck closed. Please google for suggestions on how to fix that. Its a simple process of loosening some bolts and tapping on it with a metal object or hammer. That may work. Please google for detailed writeups and diys with pictures on this.
Thanks for the information. It is 5:30 am. I can not sleep thinking about it! A few more question please.
Is there any reason that a cooling system will not be able to eliminate all the air?
If there is a head gasket problem, can air be being introduced into the system as it trying to be bled?
I researched a "ticking" sound coming from the top,front of the engine. Most popular explanation is a loose spark plug followed by lifter, loose belt, lose pulley and water pump going bad.
If it were the valves, common opinion (internet) says that it is not a problem and some suggest a 5W50 oil to cure the noise.
The spark plug is easy to check.
How much slack should be in the belt? Isn't there just one adjustment position?
I have always thought that the exhaust contained my vapor than I liked but it has been doing that for a long, long time.
It was cool and we had some rain and mist conditions yesterday but the BMW did it much more than my truck.
Wouldn't I need to loose considerable coolant to make the car overheat? Assuming I have the air out of the system.
Why can the engine run for more than an hour at idle (as I tried to bleed it) with the temp gauged pinned at the 1/2 mark but run a little hotter when on the road (and eventually overheat)?
I would think that the engine would cool better while while being driven gently. (more air flow and coolant flow) Is that situation an indicator of a bad water pump?
The pump can not keep up? Will a bad (weak) water pump make it harder to bleed the system also?
I will report back. Thanks again
These are good technical questions. However, I've decided to answer this later. I think you're overthinking this at this stage. However, I will say one thing. If your engine has had vapour out the tailpipe all the while, and was not losing coolant abnormally, then its probably fine and is not a symptom behind your current issue....that would be a safe assumption.
Now, back to your car. I'd like you to do the following. Firstly, bleed your radiator the way you should. Secondly, let the car idle for 30 minutes with the air conditioner switched off....monitor the temp gauge. Third, drive the car for 30 minutes and see if its ok.
Before all of this, check your fuse box and ensure that your auxiliary fan fuses are working perfectly.
Another thing....if you've been adding too much water to your radiator, please put some cheap off-the-shelf coolant in right away. Spend $5 or less. Maybe you could get that before you begin the bleeding process. Coolant holds higher temperatures better.
After that please report your results.
There is a good possibility that you may just have a buggy temp gauge. I had that a few days ago and luckily I remembered that I had a spare that I managed to dredge out. I swopped it in and it almost works perfectly (almost). You may be having the same problem. I don't trust your son's reports of the temp situation, I believe if you were there you would have a better global diagnostic sense of things. I recall that this is not the first time that you've worked on his car, so I believe you're the man when it comes to machines, so please get behind that wheel sir. :)
Please do the stomp test and see if there are any interesting codes stored on your car that might be relevant to all of this.
I will follow your instructions. I researched the heater valves and plan to flush the heater core. There is an article on Pelican which explains this and also how to remove and clean the valves.
Question: If the three hoses coming from the valves and intake are all hot, does that indicate that the valves are open?
If so, why heat to only the driver side?
Is the heater core seperated into two halves which are fed by the two hoses from the valves?
If the metal pipes under the panel near excelerator are hot , are valves operating? I do not want to do unnecessary work.
Could one side be gunked up?
I plan on flushing the system after I get it to run with out overheating.
Is the engine block drain very difficult to get at?
I will get to work tjis am and report back.
I'm afraid I can't properly answer your other questions. I'm not too sure about the heater valve system. Others here can help surely.
It is, of course, quite possible that some of your pipes are 'gunked up' as you say.
Lets kill the overheat issue first.
Hi Larrick. Here are some answers to the questions you asked earlier. I guess you'll only read this when you're back from running your car. :)
FYI a cooling system will never be able to eliminate all the air that it has. Engines are designed with that in mind. Only large air pockets will cause damage to the cylinder head. There are tiny ones being created and collapsing all the time in the extremely hot environment of the cylinder head. All of that is factored in. Normal bleeding as described here and/or the Bentley manual, by normal people, and without special equipment, is all that a normal cooling system requires to be happy.
Hmmmm no HG issues do not introduce air into the cooling system, but cracks in the cylinder head might. With the rad cap off and the engine at idle, do you see little bubbles appear in the expansion tank (not the bleed screw) ? If so, those bubbles are from combustion gases being squeezed through a crack in the combustion chamber that leads to a coolant passage.
The ticking sound that you're referring to could be your vanos unit being temperamental. Belts generally cause squeaky sounds, and even if they are ticking sounds, they will sound kinda squeaky. lol. It is very very unlikely for a spark plug to get loose once installed. I've never heard of that. Anyway, if your car drives well, it is unlikely that anything related to the spark plugs, ignition coils, etc, is at fault.
You do not have valve lifters as you're using a twin cam engine. The M20 E34s had that. The solution to valve lifter noise is not to change the engine oil, but to have the valve lifters tightened down to correct tolerances using a feeler gauge. This needs to be done every 50k I believe.
A water pump going bad is unlikely to generate alot of noise that you cannot easily trace to the water pump itself while standing over the engine. I could be wrong here though but I would think so.
It is not logical for the engine to be fine at idle but overheat while driving. The cooling effect of onrushing air is far far greater while driving and more than compensates for the higher rpms. If this is happening, and you're not losing coolant , then its fair to say that your water pump or thermostat is busted and insufficient heated coolant is circulating out of the head into the radiator to be cooled. Check if you're losing coolant when you stop the car after it overheats, then gently loosen the rad cap by 1/4 turn, and then another 1/4, to relieve the pressure, wait 5 minutes and loosen more, and eventually you'll be able to remove it without everything spilling out, and you can see how much coolant you've got left. If you've not lost any, then its a simple matter of the water pump or the thermostat. I would advise that you change both for peace of mind.
Yes, a bad water pump will make it harder to expel air from the cooling system. But sir, please, don't worry about air in the system. It is very rare from what I've observed. I've done substandard bleeding of my radiator before, driven it for a week, done another bleeding and noticed TONS of bubbles, and I had no problems for that week.
The exhaust is not supposed to contain any vapour at all, especially after you stop the car after a drive. If its always been that way...hmm.
Please do the stomp test and see if there's any interesting error codes stored on your computer. Who knows ? Something relevant might be there.
The belt should have no slack whatsoever. It should feel tight to the touch, you almost shouldn't be able to move it laterally or upwards (just the tiniest movement). You should be able to flick it with your thumb and it will feel sharp. If you don't have that, you've got a problem. Not a big one, but fixing it will improve your drivability. The problem may be buggy pulleys (not likely), buggy tensioners (probable) and old belts (probable). One simple way to tell if your engine belt system is working perfectly is to use fan belt spray on it. Spray it everywhere with the engine off and when the engine is on (be very careful). See if any noises that you mentioned earlier have disappeared. If they have, then you've got something to look at there. Your car will also drive better with the fan belt spray on it.
I'm not sure what you mean by "adjustment position". You must refer to the tensioners over there. I believe that there are at least two automatic tensioners in the E34 (m50) and may be more...not sure. If they are in good shape, the belts will become tight once the tensioners are released. If they are in good shape but the belts are loose, the belts are the problem, and you might have the wrong belt on your car (it happens).
Yes you would need to lose a fair bit of coolant before overheating sets in, assuming that there are no large air pockets left, and that your water pump and thermostat are working correctly. Any one of those elements being busted can easily lead to overheating situations.
Thanks Roberto. I am still at the computer doing as much research as possible before I go.
I read your post on the 3 step radiator flush and will do that. I did notice (yesterday) while working on the heater hoses ,what I think may be the electrical connection for the auxiliary pump hanging lose. It is a female two prong connector which I though may have been for an accessory which the car did not have.
That was before I knew that there even existed an auxiliary heater pump.
I also read your expose on coolant. There was a long and exhaustive conversation between you and an engineer.
I am glad I stayed long enough to get your latest information.
I think the belt was loser than what you describe. I will check
I will really leave soon and report back.
If your engine overheats, and you lose coolant, do not replenish cold water into a hot engine. Wait for the temp gauge to drop to the middle mark. Half an hour should do it. If you pour in cold water while the engine is overheated, the cylinder head will probably crack.
The engine started right away and ran perfectly smooth. No "ticking" noise and no exhaust vapor.
After 1 minute there was slight vapor at exhaust.
After 2 minutes less vapor and then none or almost perceivable if you looked hard.
5 minutes, top hose warming, no bubbles in expansion tank (none appeared through out process) engine sounds great
15 minutes, needle steady at 1/2 mark lower rad hose still cold
20 minutes, air bubbles begin at bleeder
25 minutes, "ticking" noise begins steady like a drum beat, not very loud
30 minutes, bottom rad is warming and some vapor is viable at exhaust (it is a little cool and overcast)
some heat at feed hose to heater valves.
There is NO auxiliary pump, only the electrical connection. l lifted the valve assembly and NO pump.
I assume that it went "in line" at the feed hose. I will try and locate a picture.
Bubbles continue from Bleed valve 1 and 1/2 hour.
I run rmps up to 2000 and continuous feed expansion tank with slow running hose.
The temp gauge has not budged from the 1/2 mark all this time.
I take the car out for a test drive:
I get heat at the heater but still only on the driver side although all three hoses are very hot.
The return hose to the block is not very hot, barely warm.
The needle begins to move toward the 3/4 and after a couple of miles begins to get toward RED.
I stop and let idle and the temp begins to fall.
As I drive back the needle begins to climb again.
I pull in the drive way and let it idle and open bleed valve slightly, very hot water and steamy.
I bleed some more hoping that the run has forced any air pockets out..just more and more bubbles,
There is no vapor at the exhaust at all, bone dry.
The top rad hose seems soft and empty.
The needle quickly steady at 1/2 and I am able to open the rad cap with little problem after bleed valve release.
I turn off engine and look for leaks, none found.
I am baffled, there must be air entering the system.
I am going to take it to a mechanic for a diagnostic $150.
Before I do....any ideas?
Very good chance it is the headgasket from what you describe.
I am bringing the car in early Monday morning. I fear that you are correct in your diagnostic. The water vapor is a large concern but it has been doing it for a very long time and is not consistent.
I observed for hours today and most of the time there was no obvious sign of vapor. I think that I am just wishing. I believe that the water pump is bad as well.
There would have had to been clouds coming from the exhaust to lose enough water to cause the over heat alone.
My guess is that the pump is not strong enough to "fill" the top radiator hose and air remains in it and also in other areas of the system because there is not enough force to properly bleed the system.
The volume is OK at idle but cannot provide the cooling needed under load and higher RPM.
I will have the answer on Monday evening so if anyone wants to hazard a guess, it might fun to see who is right.
I think I have provided all the information needed.
It may be a number of things. I have no record of any work on the cooing system.
It is the inability to bleed the system which has me perplexed. Hours and hours of bubbles!
Is air being sucked in through the head gasket?
I just drove it 3 miles , non highway, to my house. It was still warm from earlier and ran very normal with the needle at 1/2.
Test the thermostat and get the radiator and heater core tested for flow. Wrong coolant will damage the radiator if it is aluminum. Test fan clutch and electric fan at both speeds. Change the water pump if it is suspect. Do a compression test wet and dry and a leak-down test (to rule out gasket and cracked head problems.
And you can get water in the bore from a blown head gasket without water in the oil, but you will probably have a skin of oil in the water. (Western Australia - Home of corroded cylinder heads and blown head gaskets)
Thanks for the advice. I am resolved to take it to the shop on Monday. Pretty much on orders from my wife as I would have to neglect my actual job to continue troubleshooting.
The shop is charging $128 to diagnose the problem. The owner has had a 1994 525it in the past and has given me some valuable time and advice before and did not charge. I gave him a twenty for beer.
This the first time that I have had to admit defeat and take it in. I do like my wife's cooking.
I will post the diagnosis on Monday or Tuesday.
Good luck, bro.
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