88 735i overheating - SOLVED

[jeanro]

For a while I put aside the overheating problem focusing on fixing some other problems on my newly acquired 88 735i, manual transmission. So far I have bleed the system,replaced the thermostat, 2 visco fans, but...still overheating. The top 2 hoses are hot when overheating, but the radiator itself and the bottom hose are cold. Should I pull the radiator? Is there a way to testing it before taking it off the car?

[SergeBMW]

How exactly did you bleed the system? If not properly bled it will always overheat.

The top hose is "hot block" water coming from the engine block, bottom hose is the "cooled" water heading back into the system. Are the bottom hoses ambient temp? They should still be getting quite warm. If you pull off the bottom hose, coolant should flow out unless it is clogged. (have not seen much of this)

-How about the water pump? Has it been replaced? May have a bad impeller.

-Are you running the A/C when it overheats?

-Have you checked to make sure the lower hose is not kinked?

-Does the Aux Fan turn on?

-Where is the needle reaching?

[jeanro]

[QUOTE=SergeBMW;29849325]How exactly did you bleed the system? If not properly bled it will always overheat.

The top hose is "hot block" water coming from the engine block, bottom hose is the "cooled" water heading back into the system. Are the bottom hoses ambient temp? They should still be getting quite warm. If you pull off the bottom hose, coolant should flow out unless it is clogged. (have not seen much of this)

-How about the water pump? Has it been replaced? May have a bad impeller.
Serge, I do not know when it was last replaced.
-Are you running the A/C when it overheats?
The A/C compressor is not engaging probably due to empty system.

-Have you checked to make sure the lower hose is not kinked?
I did more bleeding, and apparently I have managed to open the radiator circuit ( I believe) since now the radiator and the bottom hose get hot.

-Does the Aux Fan turn on?
I will check on that
-Where is the needle reaching?
Before doing the bleeding, the needle was going really fast to the middle of red. Now, after bleeding, the needle stays at the beginning of red. I want to mention that after I purchased the car I emptied the cooling system (drained it at bottom of the radiator), and fill it with water.
I think I will take the water pump off...what should I look for?
Thank you

[shogun]

water pump: depends on the design. There were older plastic pumps (now they are o.k. with better material) where the impeller got lose on the shaft, so the shaft was rotating, but the impeller not or only slightly. Bearing can fail, just had that on my M3, would not turn the water pump by hand almost. Impellers break. https://blog.bavauto.com/4020/bmw-6-...p-replacement/
Overheating troubleshooting http://www.bmwe34.net/E34main/Trouble/Overheating.htm text copied:
A major problem with the Bmw E34/E32 especially the BMW M30 3.5l out of the 535i: overheating.
Don't expect the headgasket to last long in these conditions. The temperature needle should be at the 1/2 mark all the time. If the needle is near the 3/4 mark or red area, you have an overheating problem, fix it soon.

On the BMW E34 525i 92 on and the E36 325i/is with M50 engine, the engines were fitted with plastic impellers waterpumps. These waterpumps fails, the impeller desintegrates and you are left with no waterpump at all... the engine overheats. You need to check that you have a waterpump with metal impeller. Change your waterpump ASAP if yours has a plastic impeller.

Understanding the cooling system:
• The waterpump (centrifugal type) is driven by a belt. It allows the coolant to circulate.
• The thermostat controls the coolant flow into the radiator. Closed when the engine is cold (nothing goes in the radiator, open when the engine gets warm to flow the coolant inside the radiator and cool it down.
• The primary coolant fan is mounted to the front of the waterpump with the fan clutch.
• The fan clutch is a viscous fluid type that control the speed of the fan based on engine compartment.
• A two speed auxiliary cooling fan is mounted in front of the condenser. It is uses when the A/C operates and when coolant temperature exceeds 196F (91C)
• The fan shroud is also an important item not to overlook: the presence of a shroud, with about 1/2" to 3/4" clearance between the tips of the fan blades & the shroud opening, and the fan inserted about 1/2 way into the shroud opening is essential for efficient cooling performance.

First: make sure that your radiator is in good condition, check the belts, the hoses and the coolant level. Make sure that there is no coolant leaks. Check the condition of the shroud for cracks & its proper installation.
Car fluid or coolant circuit element just changed:Your overheating is probably due to air trapped into the coolant circuit. Use the bleed screw to bleed the circuit. Then bleed again, again, again and again.

Nothing had been changed, car is overheating while idling or heavy traffic:
1. Check that the thermostat works and opens.
2. Check the fan clutch.
Car overheating while driving. Not stop and go.
1. Bleed the cooling circuit.
2. Check the thermostat.
3. Check the water pump.
4. On the 535i, check the bypass hose located and attached just above the upper hose neck on radiator and runs along the inner walls to the Resivior tank. If it is plugged, the car will overheat.
Overheating with A/C on, or very high temperature only.
1. Check that the auxiliary fan is working properly(Bentley manual page 170-4).
2. Check the fan clutch.

How to check the thermostat:
A slow working thermostat is hard to diagnose. When the engine is warming up and the temperature needle is near center, touch the top radiator hose. If hot, the thermostat is working (could still be a slow one). If there is cold area in the hose or radiator, check the thermostat.

How to test the fan clutch:
Sorry guys, the newspaper test is not reliable. If the thermostat doesn't work or is slow moving, the fan clutch will fail the newspaper test and will spin freely don't even bother explaining how it is done as it is dangerous.
What you should do:
1) make sure that the thermostat is working!
2) when the car is cold, the fan clutch should turn with a small resistance and not spin freely.
3) Let the car idling and the hood not closed but down. After 5-10 min, the temperature will rise at the 1/2 mark, check that the fan is blowing a LOT of air inside the engine compartment and increase in noise level, no need to put your hands, you will feel it. If when the temperature hits the 3/4 mark, the fan is not blowing a lot of air, that means that: either the thermostat is not working or slow, or the fan clutch is bad.
Bypass hose modification: (Thanks to Dave Smith) Picture from Gale
Dave enlarged the hole on the end of the pipe from the radiator to the expansion tank.

The pipe that runs from the radiator to the expansion tank is about 1/4 inch diameter (internal) , but just as it enters the expansion tank it reduces in size down to 1/64 inch diameter. this pin hole is what was blocking and causing overheating... I have enlarged the hole by running a 1/4 drill down the pipe and this should prevent any futher blockage.

Great Overheating write up from Arnold Matusz.
The interesting thing about how this all began is that I gave my car for a little test drive to a friend who normally drives like crazy.
When I drove the car everything seemed allright, but when he gave me the key and I got into the car, the engine coolant was so hot that it would probably have bent the water indicator needle in my dashboard. First I thought he really stood on the gaspedal instead of "on the seat" and thought it needed a little cooling down time! But it was really aukward because an engine should cool itself down at 600RPM and 6000RPM aswell! I waited a bit for it to settle down but it didn't help much as I've turned the engine on ... it immediately boiled the water. So it was clear that the coolant system had a bug (thermostat, not enough coolant, headgasket, waterpump ...) As my dad is a car mechanic he immediately spotted that the thermostat was blocked in a closed position. This normally prevents the water to flush through the radiator so that the engine can't cool itself down! To change the radiator you only have to remove the thermostat housing (if you can get hold of the little seal in the housing do it, it's worth it) replace the thermostat and put back the housing. Don't forget to clean the surface so the housing can close 100% on the head ... to prevent any water leaks.
After all these have been done we noticed how difficult it is to bleed the coolant system! It was impossible not difficult! The engine was still overheating, now we thought the reason was that the thermostat is closed, there's not enough water around it (air trapped inside the system) and this is why the engine is overheating. But the thermostat was working just fine.
Then we suspected taht the headgasket had some crack and that part of the compressed air-fuel mixture from the cylinder is escaping through the crack into the coolant system! It was pretty viable as the engine overheated a few times! So we changed that aswell! But when we got back to fill up the coolant system with coolant ... it still didn't want to bleed itself through. The interesting part is that the engine could be cooled down if you use the heater in the car. The radiator from the heating system acts almost as the normal radiator, it blows loads of hot air into the cabin thus cooling the engine down! The next step was to change the water pump, although it didn't seem a very viable solution, as it gave a no good explanation why there is heating in the system!
When we took out the water pump the PLASTIC IMPELLER remained inside the head. That's when we got really happy as we found the reason for the whole overheating problem!
Overheating troubleshooting!
0 - check coolant level
1 - check if thermostat works
2 - headgasket replacement
3 - water pump replacement
4 - check the head for cracks

BUT if you've got BMW M50 (525i after 89) engine the order is a bit changed! (these models tend to have a plastic impeller on the water pump which suddenly walls down from the shat that should drive it ... so you actually end up with water not moving around at all in the egine - thus the extremely rapid overheating)
0 - check coolant level
1 - check if thermostat works
2 - check the waterpump
3 - check the fan clutch
4 - check the cooling fans for the radiator
5 - replace headgasket
6 - check the head for cracks
7 - replace engine if all these won't work :P

CAUTION: when you mount the new thermostat handle the thermostat housing with allot of precaution because it can easily crack and you end if with a leak (where not only water escapes but the engine can get air inside the coolant system which is a bag factor when it comes to overheating). When working on your coolant system and you are buying parts: always ask for a metal impeller water pump, and procure a metal thermostat housing).
IDEA: if the water pump is at faul you might cool your engine down by turning on the heater in the car ... This will let you drive it to the services, better than walking / paying for a trailer! It worked for me
unquote

is there coolant returning to the expansion tank like this? http://www.bmwe34.net/E34main/Troubl...verheating.jpg Then clean the return hose http://www.nmia.com/~dgnrg/page_19.htm

[jeanro]

Thank you guys for all the inputs you are providing: It is very helpful!!
It is 8:30 AM, Saturday, and I have relatively easy managed to take the water pump off the car. Now, the findings:
1. Pump has a metal impeller.
2. There is a bit of play and noise on the water pump shaft.
3. I have noticed that the belt turning this pump is a bit loose (I believe) because when I am taking the visco fan off, I have to push down on the belt so the pulley won't spin when I try to unscrew the fan bolt. On the same token, I had to push down on the belt to be able to unscrew the 4 bolts on the water pump pulley.

Should I still replace the pump? Any recommendation in regards to manufacturer?
I will replace the belt also since is a bit cracked on the "teeth side". It looks like I have to take all the belts off first in order to reach the belt for the water pump. Any advice on procedure and belt manufacturer?
Shogun, there is coolant flowing in the expansion tank, but I will go ahead and clean that return hose anyway.
Thank you guys again.

[shogun]

as you say, there is a bit of play already on the pump. That is a wear parts and it lasts only xx kmiles, when you change later, you have double work. A GRAF Water Pump 11519070760 costs here $40 new, http://www.rmeuropean.com/Products/1...760-MFG52.aspx
AutohausAZ has the Graf and the Saleri even for less http://www.autohausaz.com/pn/11519070761 Saleri 11519070761 - Water Pump; With Gasket; Composite Impeller (that is the new composite material) . Both are o.k. in my opinion.
Check at AutohausAZ for the belts too , see belt drive system, they have Contitech CRP http://www.autohausaz.com/search/cat...d=1012723@735I E32&year=1989

Maybe the belt was slipping for the water pump?

[jeanro]

Shogun, I bought new Graf pump, gasket and belts: I do not know if the belt was slipping...it was loose, but I have never heard a squeaking noise.
Any diy advice on replacing the belt? It seems to me that all the other belts need to come off.

[shogun]

Maybe someone with an M30 can chime in for the belts, or see the workshop manual https://www.bmwtechinfo.com/repair/main/

[pandaboo911]

88 735 here, you'll have to remove the AC and PS belt, but it's super easy. Just don't strip the tensioner bracket.

Try putting a roll of newspaper in your fan, it shouldn't be a able to stop the fan.

Elevate the front of the car and bleed it before replacing any stuff.

Check that you have no coolant leaks anywhere

[shogun]

DIY with pics an an E34 535: V-Belt Replacement And Adjustment http://www.exx.se/maintenance/v_belt/index.shtml
http://www.bmwe34.net/E34main/Mainte...ce/V-belts.htm

[jeanro]

Thank you guys,
It seems that the parts will arrive tomorrow. I will keep you posted with the progress

[jeanro]

Ok, Update time.
I have replaced the pump, belt, and did a refill of the system: car is still OVERHEATING. I have noticed that the brand new BEHR visco fan is practically doing...nothing. This is the second one installed, and if at the very beginning was "pushing" air when car was started from cold, then you would be able to stop it with the rolled paper when hot, now it can be stopped at any time (cold or hot) with paper or bare hands: is worst than the original one! The first, new visco fan installed was "producing" the characteristic noise noise of high air volume eing moved, so I know what to look for, but this one is not doing its job. Any good experiences with visco fans other than Behr? Your input is really needed. Thank you.

[shogun]

Sachs is a good one. On *bay search for BMW Fan Clutch Sachs/ZF OEM E32 E34 E36 E39 E46 11527505302 $86.99
On the other hand: Some years ago I bought a cheapo fan clutch made in China for a friend, works in his 750 without any problem. No name ones also on the bay starting prices are $26.00, of course there are many manufacturers in China and you can be lucky or unlucky with it.
Make sure the belt is correctly tightened.

[jeanro]

Sachs is a good one. On *bay search for BMW Fan Clutch Sachs/ZF OEM E32 E34 E36 E39 E46 11527505302 $86.99
On the other hand: Some years ago I bought a cheapo fan clutch made in China for a friend, works in his 750 without any problem. No name ones also on the bay starting prices are $26.00, of course there are many manufacturers in China and you can be lucky or unlucky with it.
Make sure the belt is correctly tightened.

Shogun, I will go ahead and buy a Sachs visco fan : is the part number 11527505302 the right one for my car (88 735I )? Real OEM gives me something different, but I know that sometimes part numbers are intertwined...
Thank you.

[shogun]

11527505302 is not listed for E32, but it is the design with 3 bolts http://www.realoem.com/bmw/enUS/partxref?q=11527505302 might fit (?)
OE comparison numbers BMW OE-11 52 1 709 499 ,BMW OE-11 52 1 719 046 ,BMW OE-11 52 1 719 269 ,BMW OE-11 52 1 740 963 ,BMW OE-11 52 7 505 302
3 (E36) (150 - 321 PS, 3 (E46) (150 - 231 PS, 3 Cabriolet (E36) (150 - 321 PS) 3 Cabriolet (E46) (170 - 231 PS,3 Compact (E46) (192 PS,3 Coupe (E36) (150 - 321 PS,3 Coupe (E46) (150 - 231 PS,3 Touring (E36) (150 - 193 PS,3 Touring (E46) (150 - 231 PS
5 (E34) (129 - 192 PS,5 (E39) (136 - 231 PS,5 Touring (E34) (150 - 192 PS,5 Touring (E39) (136 - 231 PS,7 (E38) (193 PS,X5 (E53) (222 - 231 PS,Z3 (E36) (150 - 321 PS,Z3 Coupe (E36) (192 - 321 PS
https://www.autoteiledirekt.de/sachs-1219507.html

[jeanro]

Update time- New SACHS visco fan has arrived, and is the first one is actually working : after I installed it, I turned on the car and noticed the increased noise and air volume coming from the fan. As the engine warmed up a bit, the noise and air volume has decreased. With the cabin fan to maximum speed and the heat also at maximum, I checked to see if a stream of coolant comes into the expansion tank via the return line: strong, constant jet of coolant is noticed coming into the expansion tank. As the coolant temperature gauge has reached the mid section ( expansion tank cap still off ), the coolant was flowing strong into the expansion tank from the return line. At some point ( after about 10min. since I started the engine) the needle goes past the mid section and visco fan comes on as I noticed the noise and increased air volume again. I hoped that temp will come down, BUT it kept going up to really close to red zone and stopped there: I left the car running and noticed that the visco fan comes ON and OFF for about 5 min ON followed by 3-4 min OFF. The needle still close to red zone, and at some point when the coolant temp warning signal was displayed, I shut the car off. So, the car is still overheating, but why is the temp staying at the red zone even when the visco fan is pushing air strong ? Why is the fan going ON and OFF following a heating/cooling normal cycle, but the coolant temperature needle stays in the upper part of the gauge without following the visco fan cooling period?
As I am running out of ideas, I would really appreciate your input again.

[Sansouci]

I don't have this engine, but I found that Harbor Freight has an infrared non-contact thermometer for about $20 (with coupons, on sale) so you can get a better idea of the temps in the hoses and across the radiator.
Does your rad still have the oem fan shroud? That helps to direct the air flow. When you are testing, keep the rad cap on (is it in good shape?), When you did the mechanical work, did you flush the block? I think the block drain is between cylinder 5 & 6. Are you running 50/50 antifreeze, Evans waterless or just water?

[jeanro]

Sansouci, I will go ahead and buy a thermometer tomorrow in order to check the engine temperature.
Yes, I still have the OEM fan shroud, a bit cracked....but all there. The cap seems OK to me for what I can tell by looking at it. I did not flush the block, but the return flow stream into the expansion tank is constant and strong, which makes me believe that water pump is pumping fluid without air. Right now I have 50/50 antifreeze/water.
I will reply back with temperature readings tomorrow.

[shogun]

visco fan works, how about the aux fan then when it get's hotter? You can test it http://www.nmia.com/~dgnrg/page_20.htm
some years ago I had the problem that the aux fan did not come on in traffic jam in hot summer and the temp gauge needle went past 12 o' clock. First I thought it is one of the 2 relays for hi or low speed or the aux fan resistor. Turned out that it was just oxidation of the spades of the relays and on the pins of the plug at the aux fan, where the wire loom goes from engine bay. Sprayed all with Contact Enhancer, Conditioner & Protector like DeoxIT Gold and all was working again.

I also use a HF non-contact thermometer, very good for checking heat transfer, just point with the laser pointer on the hoses and the areas of the radiator and you immy have the results.

[cirrusblau]

Why aren't we suspecting a head gasket failure at this point? Or at least diagnosing for it. Also make sure that the radiator is not clogged.

[jeanro]

Cirrusblau, I really hope the head gasket is not the case, but while at Harbor Freight to buy the thermometer today, I will also buy a compression tester. I have no idea how to replace a head gasket, nor I have ever done this before...Should the gasket be the culprit, shouldn't the coolant be contaminated with oil, or the oil with coolant? Besides, both fluid levels stay the same. Is there a possibility that outside air gets into the coolant circuit?. Today I drove the car around my neighborhood, and for the first 5 min. or so as the engine warmed up, the needle went up and initially stopped before the gauge mid-section for a couple of minutes: unfortunately, it kept creeping up to the red zone.

[shogun]

Basically that is a good sign, that oil is not contaminated with coolant and vice versa and that both fluid levels stay the same. Outside air should not get into the system as the system is under pressure.
A bit far fetched idea: could it be just a crazy/bad temperature feeler or he cluster is bad for the temp gauge?
You will see more when you have the thermometer. If that shows the same temperature in the area where the temp sensor is and the cluster indication goes up, then it is just a fault of wrong indication (if you are lucky).
Here are the test data for the blue sensor for temp indication http://www.e32-schrauber.de/bmw/s-tempsensor.htm
2,5 kohm at 20 degree C http://www.e32-schrauber.de/bmw/date...u-2_5-kohm.png

[cirrusblau]

I think there are some instances where coolant contamination or oil contamination is a clear cut sign of gasket failure. I think I've read somewhere that the gasket can fail between the combustion chamber and coolant hole. What happens is the combustion leaks in the coolant and heats it up pretty quickly. It could be a possibility but I think you try to do the easiest things first as shogun suggested.

Changing head gasket on an M30 is fairly easy and can be quick if you know what to remove and don't have to remove. I've done this before, you can finish this job for a whole day if you have all the parts needed.

[jeanro]

Update time: Well, Last Sunday I was supposed to go ahead and buy the thermometer + compression test for the engine....It did not happen because the night before "I had a dream"....not really, but I remembered that somewhere in between the second and third Visco fan I did replace the coolant temperature sensor with a brand new one. Compiling this almost forgotten piece of information with the fact that the new Sachs visco fan was actually cycling ON/OFF, I went ahead and I put the old temperature sensor back in the car. Hard to believe, but now, the coolant temperature sensor needle sits nice and constant at mid level!!! No more overheating !! I took the car out for a couple of days around the neighborhood at about 25 MPH, then I went on some side streets at 60 MPH and is all good.
Conclusion: the problem with the cooling system was a bad visco fan: everything else was cased by two defective brand new Behr visco fans, and also a brand new and defective temperature sensor.
Now, a glass of red wine later, let's move to the next task: fuel gage is not indicating... I will go ahead and remove the fuel sender from the tank and see what is going on with it: anything that I should be aware of while doing this?
Thank you all for all the advice given: it was very helpful, and kept me from sending the car to the c.....r. Now, I can move further with fixing it and having it back on the road.

[shogun]

There are 2 temp sensors and they have different part numbers, 1 is for the DME and one is for the temperature gauge in the cluster. They act different, you need the right temp sensor in the right position.
12 ENGINE COOLANT TEMP SENSOR 2-POL 12621710535
14 Temperature sensor, water 13621709967
and in case your car has EML it even has a third temp sensor, For vehicles with Electronic engine-power regulation =Yes
16 Temperature sensor, water M14X1,5 12621288158
http://www.realoem.com/bmw/enUS/show...diagId=11_4616

http://www.e32-schrauber.de/bmw/s-tempsensor.htm

Edit; Bentley manual page 170- 4 and 5:
1.. temperature gauge sender in thermostat housing
2. engine coolant temperature sender ECT to DME
3. EML coolant temperature sensor
so where the hose is connected, first first one is 3, then 2, and 1. If you do not have EML, the one closes to the hose is item 2 for DME, and the one farest away is for the temp gauge.
but realoem shows it a bit different http://www.realoem.com/bmw/enUS/show...diagId=11_4616
coolant temperature sensor wire colours
1988 -1992 M30
gauge sender: brown/violet-brown/yellow
ECT = DME: brown/red-brown/orange
EML sensor: brown/red-blue/violet

12621710535 2 pin, [mm]:M 14 x 1,5, Nennspannung [V]:12 Widerstand/resistance [Ohm]:5000, 544
13621709967 BOSCH Temperature Sensor - Coolant (20 deg. C / 2500 OHM) , 2-pin, M12 x 1,5


fuel sender
http://bmwe32.masscom.net/maxf_website/gauge.htm
http://bmwe32.masscom.net/johan/fuel...el_sender.html