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Just idling in your driveway doesn’t produce as much engine heat as driving 40-50 MPH.
With the AC on there is a lot of heat produced that blows past the engine radiator which adds to the heat the engine produces.
Use your Foxwell to monitor the temp sensor in the lower radiator hose with the engine at operating temp, then switch the AC on. You should see the coolant exit temp increase.
 

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Discussion Starter · #22 ·
I’m trying to locate the function I’m my scanner for engine temp but haven’t found it yet. In my drive in to work this morning it was a little cooler and my AUX fan wasn’t running nearly as hard but was still on when I parked. The more I think about the issue the more I think it’s simpler than I’m making it. I recall the previous owner last year telling me he recharged the refrigerant, AC worked fine so I never gave it another thought. I think the system is overcharged just enough to still give me good AC but it’s too much for the system to run properly hence the overheating when the car is sitting in traffic and then able to regulate itself quickly when the a/c is off. I have a cheap set of harbor freight gauges that gave me a high reading on the low side. I’m going to see if there’s a shop around that can take a look at it for me today and get the low side pressure correct or perhaps diagnose the ac system if overcharged isn’t the problem.
 

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Discussion Starter · #24 ·
Shop said it was a bad AUX fan, the mech said when he activated it, it rocked like 3 or 4 times before starting up. Then he said he tried to run it at 60% percent and it ran at that speed but then slowed down.
 

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Another issue to check is the cap on the coolant bottle. The seal on the cap gets old and leaks, at least it does on the e36. The pressure is what forces the coolant back into the system after driving. If the issue is not addressed you will slowly get an air bubble in the system, which can run with a surprisingly low amount of coolant if not sitting in traffic.

What I do with all of my cars is at some point I turn the heat on full for just a few seconds. The air pocket will migrate to your heater core first and if you don't get hot air when it is on you have a low coolant issue. Make sur you have all of the proper setting for heat and the check only takes a few seconds to verify. Ihad this happen to all of my e36 chassis wich are of similar vintage to you car. Won't hurt to check













































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So I googled myself down a rabbit hole trying find a similar overheating issue as mine but nothing that matches. In the last week temperatures have ranged between 100F - 107F, I’ve been running my AC in my 540i all summer with no issues in 80F - 90F temps. This last week in the higher temperatures when driving home from work which is a 25 mile commute and I get stuck in stop and go traffic or picking up dinner going through drive thru, the temp gauge jumps from the 1/2 mark right in the middle up to the 3/4 mark near the red. The first time it happened was in a drive through, granted Habbit Burger takes about 20 minutes to get through the damn drive through. It was over 100 out, I was in the car with my son waiting with the A/C on and the temp jumped up to the 3/4 mark. I put the car in park turned the AC off and idled the car at 1500 rpm getting the fan spinning until it cooled. It came down to the 1/2 mark after 30 seconds and stayed there the rest of the way home with the AC off. I did an experiment and I drove with the ac off when it was over 100 out and I didn’t have any issues. Then ran it with AC on got caught up in traffic and it got hot again, turned AC off, got moving and cooled back down.

I can hear the auxiliary fan for the condenser and the fan clutch both working. I suppose it could be the fan clutch getting weak, it might be original and maybe it’s only partially working which is why it’s partially overheating and hasn’t gone into the red. I’m not low on coolant, that was flushed and changed a couple of months ago. I had it at a bimmer shop about a month ago and the mech told me the water pump was leaking. I have no coolant on the ground but I know it can still be weeping a little even without the evidence. Is it possible if there’s a tiny leak at the water pump that a bubble could’ve formed in the cooling system causing reduced flow? I heard trapped air can be an issue on these cars. I would assume it would run hot regardless of the AC bring on if that were the case though even in cooler temps. I don’t think it’s the thermostat because if it were stuck it would either be hot all the time or take forever to get up to temp.

Anyway I’m thinking it’s the fan clutch so I opted to covert it to an electric fan. Just wondering what you all think about my overheating issues and thoughts about the electric fan conversion.
Correct..your coolant leak is the number one issue. My coolant would go or stay near or below halfway on nice Days. On hot days go 3/4 way. I bleed and it fixed the high temp. After u of course fix the aboce.above.
Do this check for another symtom.. When it is hot on your guage, turn off engine and then put key in run. Your aux fan should come on even without the ac on, and come hard loud, being fastest setting..mine wouldnt come on. I bought a laser gun at harbor freight, the yellow one, for like $15. My block where the engine coolant sensor was at 199 degrees. At my fan sensor to turn on the fan 176 or so. My aux coolant fan was never turning on. I don't know if it is cause I have the sensor into plastic rad, or what.. won't get into how I fixed it. But with the ac fan coming on full, and still using mech fan. I have 1/3 guage w ac on regardless of temps. Btw if u go electric fan, get ready for the drain on your alternator. Is your alternator new enough that it can handle the extra current. Keep the mechanical fan.
330hp 325i
Garrett turbo
Stage one cam
Stroker engine, 2 7l
Water/meth
Megasquirt ecm.
Stay cool
Kevin
So I googled myself down a rabbit hole trying find a similar overheating issue as mine but nothing that matches. In the last week temperatures have ranged between 100F - 107F, I’ve been running my AC in my 540i all summer with no issues in 80F - 90F temps. This last week in the higher temperatures when driving home from work which is a 25 mile commute and I get stuck in stop and go traffic or picking up dinner going through drive thru, the temp gauge jumps from the 1/2 mark right in the middle up to the 3/4 mark near the red. The first time it happened was in a drive through, granted Habbit Burger takes about 20 minutes to get through the damn drive through. It was over 100 out, I was in the car with my son waiting with the A/C on and the temp jumped up to the 3/4 mark. I put the car in park turned the AC off and idled the car at 1500 rpm getting the fan spinning until it cooled. It came down to the 1/2 mark after 30 seconds and stayed there the rest of the way home with the AC off. I did an experiment and I drove with the ac off when it was over 100 out and I didn’t have any issues. Then ran it with AC on got caught up in traffic and it got hot again, turned AC off, got moving and cooled back down.

I can hear the auxiliary fan for the condenser and the fan clutch both working. I suppose it could be the fan clutch getting weak, it might be original and maybe it’s only partially working which is why it’s partially overheating and hasn’t gone into the red. I’m not low on coolant, that was flushed and changed a couple of months ago. I had it at a bimmer shop about a month ago and the mech told me the water pump was leaking. I have no coolant on the ground but I know it can still be weeping a little even without the evidence. Is it possible if there’s a tiny leak at the water pump that a bubble could’ve formed in the cooling system causing reduced flow? I heard trapped air can be an issue on these cars. I would assume it would run hot regardless of the AC bring on if that were the case though even in cooler temps. I don’t think it’s the thermostat because if it were stuck it would either be hot all the time or take forever to get up to temp.

Anyway I’m thinking it’s the fan clutch so I opted to covert it to an electric fan. Just wondering what you all think about my overheating issues and thoughts about the electric fan conversion.
Correct..your coolant leak is the number one issue. My coolant would go or stay near or below halfway on nice Days. On hot days go 3/4 way. I bleed and it fixed the high temp. After u of course fix the aboce.above.
Do this check for another symtom.. When it is hot on your guage, turn off engine and then put key in run. Your aux fan should come on even without the ac on, and come hard loud, being fastest setting..mine wouldnt come on. I bought a laser gun at harbor freight, the yellow one, for like $15. My block where the engine coolant sensor was at 199 degrees. At my fan sensor to turn on the fan 176 or so. My aux coolant fan was never turning on. I don't know if it is cause I have the sensor into plastic rad, or what.. won't get into how I fixed it. But with the ac fan coming on full, and still using mech fan. I have 1/3 guage w ac on regardless of temps. Btw if u go electric fan, get ready for the drain on your alternator. Is your alternator new enough that it can handle the extra current. Keep the mechanical fan.
330hp 325i
Garrett turbo
Stage one cam
Stroker engine, 2 7l
Water/meth
Megasquirt ecm.
Stay cool
Kevin
So I googled myself down a rabbit hole trying find a similar overheating issue as mine but nothing that matches. In the last week temperatures have ranged between 100F - 107F, I’ve been running my AC in my 540i all summer with no issues in 80F - 90F temps. This last week in the higher temperatures when driving home from work which is a 25 mile commute and I get stuck in stop and go traffic or picking up dinner going through drive thru, the temp gauge jumps from the 1/2 mark right in the middle up to the 3/4 mark near the red. The first time it happened was in a drive through, granted Habbit Burger takes about 20 minutes to get through the damn drive through. It was over 100 out, I was in the car with my son waiting with the A/C on and the temp jumped up to the 3/4 mark. I put the car in park turned the AC off and idled the car at 1500 rpm getting the fan spinning until it cooled. It came down to the 1/2 mark after 30 seconds and stayed there the rest of the way home with the AC off. I did an experiment and I drove with the ac off when it was over 100 out and I didn’t have any issues. Then ran it with AC on got caught up in traffic and it got hot again, turned AC off, got moving and cooled back down.

I can hear the auxiliary fan for the condenser and the fan clutch both working. I suppose it could be the fan clutch getting weak, it might be original and maybe it’s only partially working which is why it’s partially overheating and hasn’t gone into the red. I’m not low on coolant, that was flushed and changed a couple of months ago. I had it at a bimmer shop about a month ago and the mech told me the water pump was leaking. I have no coolant on the ground but I know it can still be weeping a little even without the evidence. Is it possible if there’s a tiny leak at the water pump that a bubble could’ve formed in the cooling system causing reduced flow? I heard trapped air can be an issue on these cars. I would assume it would run hot regardless of the AC bring on if that were the case though even in cooler temps. I don’t think it’s the thermostat because if it were stuck it would either be hot all the time or take forever to get up to temp.

Anyway I’m thinking it’s the fan clutch so I opted to covert it to an electric fan. Just wondering what you all think about my overheating issues and thoughts about the electric fan conversion.
Correct..your coolant leak is the number one issue. My coolant would go or stay near or below halfway on nice Days. On hot days go 3/4 way. I bleed and it fixed the high temp. After u of course fix the aboce.above.
Do this check for another symtom.. When it is hot on your guage, turn off engine and then put key in run. Your aux fan should come on even without the ac on, and come hard loud, being fastest setting..mine wouldnt come on. I bought a laser gun at harbor freight, the yellow one, for like $15. My block where the engine coolant sensor was at 199 degrees. At my fan sensor to turn on the fan 176 or so. My aux coolant fan was never turning on. I don't know if it is cause I have the sensor into plastic rad, or what.. won't get into how I fixed it. But with the ac fan coming on full, and still using mech fan. I have 1/3 guage w ac on regardless of temps. Btw if u go electric fan, get ready for the drain on your alternator. Is your alternator new enough that it can handle the extra current. Keep the mechanical fan.
330hp 325i
Garrett turbo
Stage one cam
Stroker engine, 2 7l
Water/meth
Megasquirt ecm.
Stay cool
Kevin
 

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Another issue to check is the cap on the coolant bottle. The seal on the cap gets old and leaks, at least it does on the e36. The pressure is what forces the coolant back into the system after driving. If the issue is not addressed you will slowly get an air bubble in the system, which can run with a surprisingly low amount of coolant if not sitting in traffic.

What I do with all of my cars is at some point I turn the heat on full for just a few seconds. The air pocket will migrate to your heater core first and if you don't get hot air when it is on you have a low coolant issue. Make sur you have all of the proper setting for heat and the check only takes a few seconds to verify. Ihad this happen to all of my e36 chassis wich are of similar vintage to you car. Won't hurt to check













































i
Last thing, make sure your mechanical fan shroud Is mounted properly. The shroud cause a air pressure difference and and this difference sucks in the cold air, otherwise it is basically doing nothing.
 

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Not a bubble caused by a weeping water pump.

Outside (ambient) temps have almost nothing to do with how hot or cool your car runs. You have a different problem.

Fan clutches work great...you should test yours with a roll of newspaper..If you can stop the fan with a hot engine with the roll of newspaper....get a new fan clutch, but not a cheap one or one made by Meyle..Also don't replace it with an elec. fan..

You can test your aux fan (in front of radiator) with INPA and other 2-way scanners. You should test it.

If your fans work as they should you may have an obstruction or a faulty water pump.
Any chance anybody ever used stop leak or similar in the past? I have pulled hardened stop leak the size of my thumb out of E39 cooling hoses. Why did you flush your cooling syst
So I googled myself down a rabbit hole trying find a similar overheating issue as mine but nothing that matches. In the last week temperatures have ranged between 100F - 107F, I’ve been running my AC in my 540i all summer with no issues in 80F - 90F temps. This last week in the higher temperatures when driving home from work which is a 25 mile commute and I get stuck in stop and go traffic or picking up dinner going through drive thru, the temp gauge jumps from the 1/2 mark right in the middle up to the 3/4 mark near the red. The first time it happened was in a drive through, granted Habbit Burger takes about 20 minutes to get through the damn drive through. It was over 100 out, I was in the car with my son waiting with the A/C on and the temp jumped up to the 3/4 mark. I put the car in park turned the AC off and idled the car at 1500 rpm getting the fan spinning until it cooled. It came down to the 1/2 mark after 30 seconds and stayed there the rest of the way home with the AC off. I did an experiment and I drove with the ac off when it was over 100 out and I didn’t have any issues. Then ran it with AC on got caught up in traffic and it got hot again, turned AC off, got moving and cooled back down.

I can hear the auxiliary fan for the condenser and the fan clutch both working. I suppose it could be the fan clutch getting weak, it might be original and maybe it’s only partially working which is why it’s partially overheating and hasn’t gone into the red. I’m not low on coolant, that was flushed and changed a couple of months ago. I had it at a bimmer shop about a month ago and the mech told me the water pump was leaking. I have no coolant on the ground but I know it can still be weeping a little even without the evidence. Is it possible if there’s a tiny leak at the water pump that a bubble could’ve formed in the cooling system causing reduced flow? I heard trapped air can be an issue on these cars. I would assume it would run hot regardless of the AC bring on if that were the case though even in cooler temps. I don’t think it’s the thermostat because if it were stuck it would either be hot all the time or take forever to get up to temp.

Anyway I’m thinking it’s the fan clutch so I opted to covert it to an electric fan. Just wondering what you all think about my overheating issues and thoughts about the electric fan conversion.
I have a 2000 528i. manual. I had my aux fan fail last year, In hot weather the AC would cut out at a long stop light. Didn't see a temp rise during such a short stop. The aux fan does not make much noise in operation, ever. It runs at one speed and is turned on and off by a sensor switch imbedded in a port in the radiator hose. In my car it is hard to see the aux fan running. It is pretty well hidden from view. If your car sounded like a piper cub, it was the clutch fan fully engaged, not the aux fan.
I am assuming my 528i is similar in this way to your 540i. If so, I would look for an aux fan or temp sensor switch failure first.
 

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My car is a 1990. I have a 2 speed fan. Sorry to confuse u. I checked your 528i water sensor.. only one speed.
Here is my car
Meant to say catch can, and e36 pack pinion
I agree my is noisy at high speed, but not at low speed fan.
Anyhow. 540 are nice!!
Keep me posted.
Kevin
 

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My car is a 1990. I have a 2 speed fan. Sorry to confuse u. I checked your 528i water sensor.. only one speed.
Here is my car
Meant to say catch can, and e36 pack pinion
I agree my is noisy at high speed, but not at low speed fan.
At very end mispeed. turns on like last 15 sec of video into low speed
Anyhow. 540 are nice!!
Keep me posted.
Kevin
 

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I have a 2000 528i manual. A freaky thing happened last year. In hot weather the AC would stop cooling at a long red light and then start working again in a few hundred yards of driving. The aux eliectric fan had lost all its blades. They were lying in the space in front of the aux fan. No obvious cause for that, no damage in the area. The clutch-operated fan was roaring during those episodes (like a Piper cub!

Seems to me your symptoms are similar to mine. The aux electric fan is hard to see. It is hidden from easy view. It doesn't make much sound either and runs at one speed. It is actuated by an on-off sensor switch located in a port in the radiator hose. I would verify visually that the aux fan runs. If not, the sensor switch or the fan are likely at fault or there is ab electrical problem, maybe a fuse?
 

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fyi, on the 1999-2003 6 cylinder e39 engines, the aux fan is operated by a PWM signal sent to the fan by the DME, not directly from the temp sensor.
 

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It’s a 2001, I bought the fan from a small company out of California that sells on eBay. It’s a dual fan set up and comes with a controller designed to be a drop in. Not sure What quality the controller will be so I might upgrade it depending. I also think I’d prefer the fan to run at a slower speed and ramp up when needed, better on the power draw I’d think.
At 100deg + with AC on and the car not on the move there is a possibility the temperature will rise. The outside temp is not what's the problem it is the static temp around the engine that is increase to a much higher reading and hence the problem. Since this problem is not normal for your daily activities I recommend to not change the fan
 

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Discussion Starter · #35 ·
Ordered a new Mahle/Clevite AUX fan from rock auto for $225 plus tax and shipping thought that was a pretty good deal and I believe it to be an oem fan being the Mahle brand even though it’s Mahle/clevite and not Mahle/behr. My electric fan set up to replace the clutch fan also showed up last Friday. The instructions recommend removing the radiator to get the mounting perfectly flush, I was hoping to avoid removing that but it is what it is. Don’t think it’ll be to big of a deal to install, the wiring is what I’m looking forward to the least but I plan to tap into the power under the cabin air filter. Looks like the safest place to mount the relays as well. I’m going to try the probe that inserts between the radiator find that the kit came with but if it proves too inaccurate I’ll opt for the screw in thermal switch that directly reads from the coolant. I’ve heard that the probes register 20F cooler than the screw in type. Is it okay if I PM you @JimLev if I have any wiring questions?
 

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Mounting your fan right to the radiator will only cool the part the fan in mounted too.
If you can mount it in the shroud and seal the gap between the OD of the fan to the ID of the shroud it would be MUCH more efficient, as it will be pulling air thru the whole radiator.
You can PM me, no problem. We are leaving on a short camping trip up to CO in 3 hours, back Thursday night. I doubt where we’re going has wifi or cell reception.
 

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Update
Mitch PM’d me, his fan did come with a shroud.
RAZ, you have resistors and relays in your aux fan circuit because your car has a non tu engine. Once the tu engine design (1999) was incorporated no more relays and resistors.
(fixed typo)
 
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Update
Mitch PM’d me, his fan did come with a shroud.
RAZ, you have resistors and relays in your aux fan circuit because your car has a non tu engine. Once the tu engine design (1999) was incorporated to no more relays and resistors.
I would suggest you change the aux fan first and see how it goes. You may not need to change the clutch fan out to get decent cooling unless the clutch fan just isn't working. Let us know the results.
 

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Discussion Starter · #40 ·
I would suggest you change the aux fan first and see how it goes. You may not need to change the clutch fan out to get decent cooling unless the clutch fan just isn't working. Let us know the results.
I’m positive the AUX fan is the only issue with the cooling system. When I don’t run the ac it never overheats. The guy at the shop said I could run my ac while I’m driving and turn it off when I come to stops. I did that a couple of times on really hot days to test it and haven’t had any issues, so as soon as I change that fan out all should be well in stop and go traffic and sitting. The clutch fan seems to be operating as it should. I think I’ve just noticed it making more noise because it’s probably turning harder to make up for the weak AUX fan. I have a new AUX fan sitting in my garage waiting to go as well as the new electric main cooling fan to replace the clutch fan. It was something I was considering do all along anyway so this situation encouraged to just buy it and put it in.
 
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