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Discussion Starter #1
This problem has started a year ago what happens is:

The car (520i 2002) runs normally without any problems, temp gauge drops on high speed... and sometimes specially when I put some load on the engine such as accelerating to high RPM the water circulation gets locked then water starts to get out from the radiator cap and overheats and the hose gets very tough.

Parts changed:

1- radiator cap
2- water pump
3- thermostat
4- Front fan
5- Fan clutch

anyone faced or repaired the same, is there any other procedure I can do before changing the engine?

Thanks
 

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I would replace the radiator before I considered replacing the engine. The fact that the temp drops with higher speed and knowing it's not the water pump, fan or the thermostat, makes me think there is a lack of coolant flow and the radiator comes to mind first. These cars need new radiators every so often anyway and a radiator is much cheaper than an engine!

Jim
 

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Discussion Starter #3
Thanks alot jim,

I will change the radiator, although the cooling is very good I mean I think there is no lack in cooling, but the cooling system just suddenly gets locked.
 

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Thanks alot jim,

I will change the radiator, although the cooling is very good I mean I think there is no lack in cooling, but the cooling system just suddenly gets locked.
Are you sure that it's properly bleed? There seems to be some difficulty getting air out of these cooling systems.

Jim
 

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I would like to point out that the coolant temp dropping at high speeds and increased engine loads is normal vehicle operation. That is what our electric thermostats are all about. When the DME senses increased or increasing engine loads it sends power to heat the thermostat thereby opening it and lowering the coolant temp.
 

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has anyone power washed the radiator itself so to unclog whatever debris might be caught up in the fins so airflow can get through the cooing fins?
 

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Discussion Starter #8 (Edited)
ok, no one power washed the radiator yet, and regarding gauge drop on higher speeds it's not normal because the temp gauge should stay at the middle only although the coolant temp keeps changing I mean when the coolant gets too cold or too hot the temp gauge will then move from the middle point. it seems like ill power wash the radiator and if problem not solved then a motor replacement is the step.
 

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ok, no one power washed the radiator yet, and regarding gauge drop on higher speeds it's not normal because the temp gauge should stay at the middle only although the coolant temp keeps changing I mean when the coolant gets too cold or too hot the temp gauge will then move from the middle point. it seems like ill power wash the radiator and if problem not solved then a motor replacement is the step.
I agree with you, temp should hold pretty steady. If temp is rising during high speeds I'd think cooling was too little, if cooling drops during high speeds I'd think it's not cooling enough at low speeds. Motors are designed to run in a fairly narrow temp range. Deviation from that range IMO, points to something needing adjusting.

bashar you have some dope mods! You should start a BMW page on www.modificationpost.com. It's so much better than the forums.
Oh common. This forum is GREAT!! Wonderful people, great advice, seldom any discord. If you think it could be better, contribute more.

Jim
 

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ok, no one power washed the radiator yet, and regarding gauge drop on higher speeds it's not normal because the temp gauge should stay at the middle only although the coolant temp keeps changing I mean when the coolant gets too cold or too hot the temp gauge will then move from the middle point. it seems like ill power wash the radiator and if problem not solved then a motor replacement is the step.
Have you watched the coolant temp via cluster test 7? The gauge stays in the middle for temps between 75 and 113 deg C.

BTW, if the fins of the radiator were clogged with debris, there would be little cooling capacity. I doubt that that's the problem.
 

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Have you watched the coolant temp via cluster test 7? The gauge stays in the middle for temps between 75 and 113 deg C.

BTW, if the fins of the radiator were clogged with debris, there would be little cooling capacity. I doubt that that's the problem.
Yep, last time I had to replace a radiator my truck would get hot in traffic, and cool down on the highway. New radiator had it holding steady again even in Dallas summer traffic.

There are a lot of tiny passages inside a radiator that are prone to corrosion and clogging from even small debris. Higher speeds tends to bring enough air through the engine/compartment to cool things down.

Jim
 

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Are you sure that it's properly bleed? There seems to be some difficulty getting air out of these cooling systems.

Jim
I'm in this camp.. I hazard a guess that an air bubble -(possible head gasket but certainly may not be) I would guess this if t-stat has be checked temperature gauge test 7 has been verified.
 

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I'm in this camp.. I hazard a guess that an air bubble -(possible head gasket but certainly may not be) I would guess this if t-stat has be checked temperature gauge test 7 has been verified.
Good point. Then chemical test the coolant fluid for exhaust gas residue to assess the integrity of the head gasket.

If the fluids are free of exhaust contaminants then a new motor is not likely needed, and it's more likely an air bubble or a bad radiator. (Given all the other new parts.)

Jim
 

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+1. The OP should review Internet and forum info on bleeding the cooling system on an E39.

My comment of the fact that the ECU opens the thermostat at high engine demand was merely to point out that this is the reason his temp gauge was indicating a reduction in coolant temp. If the cooling system were full of coolant (bled properly), the gauge would not indicate the coolant temp change due to the buffered gauge, but it would be visible on test #7 on the OBC.

I think it is important for DIY owners to understand how their cars work so they do not think low coolant temps at high engine demand are symptomatic of a coolant system problem when in actuality it is normal vehicle operation and a properly operating thermostat and ECU. Of course, this is true for cars with an electronic thermostat. E39s of MY1999 and up.
 

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Discussion Starter #18
I like all the comments I read here they all are very helpful

Note: the water that gets out from radiator is brown color and looks dirty

I highly agree with "edjack edjack" comment, I also had a doubt that the radiator is bad but I had to change it yesterday night to be sure that it is not causing the problem. so now all fingers pointing to head gasket or engine head crack. so is there any other thing should be suspected before replacing the engine or is it better to fix mine? what do you think?


Q: will a dirty thermostat cause it stop working properly

THanks
 

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Dirt in the cooling system will ruin proper system function-clogged radiator, malfunctioning thermostat, inaccurate sensor read outs, etc., etc. You need to have the whole system power flushed and tested for proper flow including radiator, thermostat, heater core, etc.

A brand new engine will continue to malfunction if the cooling system is filled with dirt, rust, whatever.
 

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Discussion Starter #20
Thanks johnstern,

Will a faulty coolant sensor deliver a wrong temperature massage to the thermostat which damage the cooling operation?
 
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