E34 Cooling System Issues - Poor flow through radiator - Water pump issue?

[ejbrooks]

I have a 1990 BMW 535i (10/89 - firewall mounted expansion tank) E34 with some persistent cooling issues: coolant is not flowing properly through the radiator - the upper hose it very hot and the lower is cold.

Some background:

I was able to correct the issues I had about a year ago after I blew the heater crossover pipe in the dash (plastic feed tube to the heater core) all over the interior on a very hot day in traffic. This I assumed was due to the tube being 20+ years old and becoming brittle. After replacing it with a good used one I was able to drive the car for about 8 months and then I got a leak again from around the tunnel indicating the heater core or heater crossover pipe was again leaking after a 500 mile trip and I just got a chance to tackle it again.

After tearing into the dash this past weekend determined to fix my heat/coolant issues once and for all I replaced the heater core, heater crossover pipe, and all the o-rings. I no longer have the leak in the dash and I have good heat. While I was at it I replaced the auxiliary water pump, heater control valve, thermostat, mechanical fan clutch, and auxiliary electric fan - assuming that once everything was replaced I wouldn't have any issues this summer.

BUT the current issue:

I am now having some trouble getting proper flow through the radiator. I took the hose off near the water pump, stuck my finger in there and turned the water pump over by hand and can feel the impellers spinning as they should. My question is, when I spin the fan over by hand as fast as I can you would expect the water to get pushed out where I disconnected the tube but I get little to no coolant flow - is this normal or is there a problem with my water pump hindering flow through my radiator?

I know these are tricky to bleed but I have done the sequence about 10 times no with no luck (i.e. when cold, open bleed screw on thermostat housing, fill reservoir until coolant comes out of the bleed screw free of air bubbles, close bleed screw, start engine with heat on high, allow to come to operating temperature, then at idle open bleed screw and close when coolant is smooth and free of bubbles, then repeat a few times). When I hold onto both upper and lower hose at once and squeeze one or the other I can feel coolant flowing through both so I know my radiator is not blocked.

Overall:

Does anyone have any further suggestions/insight about it being the water pump (or how much water the water pump pumps when it is operating correctly), still a bleeding issue, or a what else I can try?

Thanks for your help! I really would like to get to driving this car because here in NY we don't have too many months of nice weather!

[ross1]

Water pumps on your engine are known for failure every 60k miles or so but the typical failure mode is leaking/bad bearing neither of these will inhibit circulation. Spinning the pump by hand isn't a good test. If the bearing is tight, it doesn't leak and the impeller is firmly attached on the shaft then it is fine.
The small hose to the coolant reservoir can become clogged making it tough to bled the air.
You mention replacing the thermostat, is it backwards? A backwards T stat will not open.

[ejbrooks]

Thanks for the reply! The bearing is tight, there are no leaks, and the impeller is attached firmly - I will leave the pump alone then. I assumed that it was fine since they are quite simple to diagnose I just wasn't sure if anyone has had issues with volume-output/movement of water but was second guessing myself and thought it would be worth getting a second opinion - so thank you!

I checked the small coolant hose by disconnecting both ends (at the rad and at the expansion tank) by blowing through the hose both directions making sure there was nothing clogging it and it doesn't seem to have any restrictions. Is there any benefit to increasing the diameter of this small hose to increase flow?

I also made sure that the thermostat is in correctly - the thermostat in the direction it is worked just fine the past summer making sure the trickle-valve was pointing up as well to aid in bleeding the system. To be sure - below is the orientation that I have the thermostat.

Thanks again!


[ejbrooks]

Some more updates, I went ahead and changed the thermostat once more thinking I cooked it and there is still no difference - the upper hose is hot and the lower is cold. The car doesn't overheat at idle but the hoses should as least be similar in temperature. I am afraid that if I drive it in traffic it will overheat again or bust a weak point in the system (like the heater crossover pipe which I would rather not do again.) Does anyone have any experience with these symptoms? As I said nearly everything else in the coolant system has been replaced and it has been through the proper bleeding sequence multiple times. Thanks!

[ejbrooks]

I have a 1990 BMW 535i E34 M30 (3.5L) and I am trying to determine what direction coolant flows through each hose. I just replaced the thermostat since I am having issues getting flow through my radiator. The upper hose is extremely hot and the lower hose is ice cold even after changing the thermostat. Also when touching the radiator itself only the left hand side (closest to upper hose) is hot and 3/4 of the radiator is cold just like the lower hose. I have bled, re bled, and bled again and have no additional air coming out of the coolant system indicating that it is bled properly. The overflow hose from upper rad hose to expansion tank flows properly as well.

Does anyone know what direction coolant flows through the radiator? (i.e. hot in top cold out bottom or hot in bottom cold out top?)

The car is not overheating at idle but I am clearly not getting the correct flow.

The thermostat is in the correct orientation which I have checked numerous times and there is a small hole in the top of the thermostat to aid in bleeding.

[demetk]

Remove the thermostat and check again. If the lower hose is still cold then rad is probably plugged.

[pauliescff]

Take the thermostat out and place it in boiling water to see if it opens. Also, I didn't see any mention of the radiator being replaced. If the cooling system was not maintained very well, it could be plugged.

[ejbrooks]

I replaced the thermostat with a new one yesterday and checked the old one as well in a pot of boiling water and it still worked but thought it may have been slow to open so I left the new one in. With the new one in I still do not get flow through the radiator and the upper hose is hot and the lower is cold. The previous owner replaced the radiator and I was able to drive it without an issue until my heater crossover pipe in the dash cracked again and lost coolant. Last time I had some cooling issues I took out the thermostat entirely and checked flow on the radiator and it did not seem blocked at all since both hoses were nearly the same temperature. Does anyone know what direction coolant flows through the radiator? Either in the top hose and out the bottom or in the bottom and out the top, I can't seem to find any coolant flow diagrams for this system.

[demetk]

Flow is from the top hose to the bottom hose.

[shogun]

From water pump thermostat it goes to top left of radiator. Out of radiator bottom side.
M30 6 Cylinder Engine Coolant System Bleed http://www.bmw7resource.co.uk/TechDo...d%20System.pdf
Maybe the water pump is the problem, on some models the impeller get's lose on the shaft and does not pump enough coolant anymore, also check the water pump drive belt, if slipping.

Note: I merged the 2 threads with same subject, so questions +answers are a bit mixed up now.

[ejbrooks]

Flow is from the top hose to the bottom hose.

Thank you!!

[ejbrooks]

From water pump thermostat it goes to top left of radiator. Out of radiator bottom side.
M30 6 Cylinder Engine Coolant System Bleed http://www.bmw7resource.co.uk/TechDo...d%20System.pdf
Maybe the water pump is the problem, on some models the impeller get's lose on the shaft and does not pump enough coolant anymore, also check the water pump drive belt, if slipping.

Note: I merged the 2 threads with same subject, so questions +answers are a bit mixed up now.

Thanks for the bleeding procedure! Also, when I removed the hoses leading to the water pump and stuck my finger in there with the belts off and spun it over the impeller was still fixed rigidly to the shaft and was not slipping, and with no leaking I assume the water pump is fine. Once back together with the belt tightened I do not see any slipping whatsoever.

Knowing now that the water flows from the upper hose to the lower hose through the radiator, does anyone know the degree difference I should be experiencing between the two hoses? Or am I possibly overthinking things and the radiator/fan/pump are doing their job well enough that the lower hose is actually supposed to be substantially lower in temperature? (Note: it is still chilly here at 50F I am just nervous once it gets warmer out this summer that I will have further overheating issues)

Thanks for the help everyone!

[demetk]

I could get some temperatures on the 535 between the top and bottom parts of the rad. I'm running a Volvo fan with an aftermarket fan controller. Let me know if that would be of any help.

[ejbrooks]

I could get some temperatures on the 535 between the top and bottom parts of the rad. I'm running a Volvo fan with an aftermarket fan controller. Let me know if that would be of any help.

Before I ask you to do all that, when your car warms up to operating temperature at idle/parked does the upper hose and lower hose eventually get closer together in temperature? Because my upper hose when idling for about 20 minutes is very hot and the lower still feels like it hasn't been run at all - meaning there is a huge temperature difference between the two hoses.

[ross1]

Are you actually having any overheating or losing coolant? I don't see mention of this.
It seems a good bet your pump is okay, your stat is in correctly, etc. If you aren't having problems why are you pursuing this?

[demetk]

Before I ask you to do all that, when your car warms up to operating temperature at idle/parked does the upper hose and lower hose eventually get closer together in temperature? Because my upper hose when idling for about 20 minutes is very hot and the lower still feels like it hasn't been run at all - meaning there is a huge temperature difference between the two hoses.

Just came back from the dog park and checked the black 535 while it's still idling. The upper hose is hot to the touch but the bottom hose is cool to the touch. I'd say it's less than body heat.

[ejbrooks]

Are you actually having any overheating or losing coolant? I don't see mention of this.
It seems a good bet your pump is okay, your stat is in correctly, etc. If you aren't having problems why are you pursuing this?

I no longer have any overheating and I am not currently losing coolant but that is exactly where I was last time before popping the heater crossover pipe for the second time. I am pursuing this because I have been chasing overheating issues for nearly 2 years now and before I put it back on the road for the season (the car isn't driven in the winter) I want to make sure everything is good to go (last time it overheated I was in terrible traffic and it was not pretty) - better safe than sorry is all.