overheating update: still stumped

[Mr. BILL]

For some reason, I can't post on my thread already started on the subjuct. So, I thought I'd start another.

Jeff, The t-stat is a whaller. I tested it in a pan of hot water and it works.

I decided Sunday night to start over. So I pulled all the hoses and flushed the daylights out of the block and back flushed the radiator. Some cloudy white water came out at first. I kept at it until the water coming out was clear.

I put it all back together and filled/bled it according to Bentley's proceedure. I started it up and it stayed at normal temp at idle for 5-6 minutes. I took it for a spin and didn't go 200 yds before the temp started going to 3/4. It was late, so I shut it off and went to bed.

This morning, I topped it off and tried again. Same thing, let it idle 6-7 minutes and took it for a drive. This time, I made it twice around the block before it started to get hot. Before I shut it down, I opened th bleeder screw and only a steady stream of coolant came out. I reved the engine for a bit and still no bubbles. So I'm fairly confident I have the air out. BTW, the heater is putting out copius anounts of warm air.

At this point, I think I've eliminated the t-stat and air. I have a new water pump, so I'm ruling that out as well. That should narrow it down to the radiator, fan clutch, aux fan and god forbid, they guy sold me the wrong hedad. Although the two heads are identical from the outside. It's supposed to be off n '89 325 and of course mines a '90 525, both M20's.

Clues that may help are: the hose on the lower passenger side of the radiator, never gets hot, or even warm.Same with the crossover tube. When I removed the hoses from the radiator, it took almost 10 minutes for the radiator to drain. Just a steady stream like someone taking a whiz. I don't know if it getting hot is a result of actually driving, or because after 8-9 minutes it gets hot, which it does.

I was all set to but a new radiator, but then someone suggested it could be the fan clutch, which I'll check in the morning. I'm about to give up and let my indy figure it out. However, I hate to admit defeat. So, I'm asking one last time (for this project) for any ideas.

Finally, a big thanks to all who have helped. Especially winfred and Regal. I can't thank you all enough.

[Jimmy535i]

I went through the same routine you are going through. I replaced: T-Stat, waterpump, fan clutch, radiator, auxillary fan without solving the problem. Are you getting very high pressure from the upper radiator hose? Are you sure that the coolant tempature sensor is working? Is the motor actually overheating? Are you certain that the cylinder head you installed is not cracked?

[simon-york]

I would still suspect your thermostat. If the radiator is clear but the bottom hose does not get hot and it gets hot within 200 yards it must be the thermostat - provided the gauge and sender unit are working correctly. If you place your hand on the radiator and engine are the same temperature (roughly) the thermostat is opening. If not, and the engine is hot with a cold radiator your thermostat is shut.

BTW you cannot check a thermosts by dropping it into already hot water, you have to start with cold and then warm it up.

Hope this helps.

Simon

[Mr. BILL]

Thanks guys. After some thought, reading ya'lls posts as well as Bruno's overheating article, I'm thinking it could be the thremostat too. I remember noting that when it did open during my hot water test, it only opened about 1/4" if that. That seemed less than I remember other t-stats opening. BTW, I did put it in cold water and let it heat up.

I think before I throw any more money at it, I'll invest $20 in another t-stat and try that.

Thanks again...and agian...and again

[simon-york]

Sometimes it's a question of trying a few things and then you ought to start with the cheapest.

But there is one that you may not have tried and once caught me out many years ago with a friends immaculate 1971 Triumph Vitesse convertible.

This lovely car was garaged for most of the year and only came out on sunny days. Once it began to boil within half a mile of starting. The cause? An easy one said a friendly mechanic. If it gets that hot, that soon it has to be a poor radiator cap - on our case the one on the expansion tank. With a poor seal or weak spring it no longer pressurises the water which soon reaches 100C or 212f and boils.

Another item worth checking/replacing. It is hopefully also fairly cheap. But do work out first whether the engine is really hot and whether it and the rad are the same temp (roughly)

Good luck! Let us know what fixes it.

[Mr. BILL]

I compared the two t-stats and I was wrong, thinking the one I had in there oartially opened. I did a side by side test and they both open all the way.

I'm going to check the fan clutch, then pull the radiator and have it tested.

[Bruno]

I compared the two t-stats and I was wrong, thinking the one I had in there oartially opened. I did a side by side test and they both open all the way.

I'm going to check the fan clutch, then pull the radiator and have it tested.

I don't think it is your fan clutch. IF the radiator doesn't get hot the fan clutch won't engage.

Ok, you have a M20 engine, what you willl do is the following:
Open the thermostat screw then blow with your mouth where the radiator cap goes until only clear coolant comes out. Close thescrew and stop blowing.
Do the same with the screw on the rad.

The M20 is very hard to bleed. Took me 1 hour last time I tried....

Make sure that you have the heater open also.

If the car overheats and you have no heat: AIR IS TRAPPED either from not bleeding enough or headgasket/cylinder head/block problem.

[632 Regal]

the lower rad hose will not get hot if the radiator is working, it will stay cool cause it is getting cooled down. Sounds like a circulation issue, perhaps an air pocket but as Bruno says you wouldnt be getting heat if there was.

did this thing over heat with the old head?

If not then after bleeding it AGAIN I would suspect that perhaps you may have an issue with the head gasket. Maybe it is wrong or something is blocking the flow through the head, I dont personally have any experience with it. do the aux fans come on when you put the AC on? If they dont you have a problem. If they do then try turning that on when it starts to overheat and see if it cools down. When the engine is cold and you atart it you should hear the fan, will sound kinda like a school bus when you rev it up a little.

Hope you find this soon, driving me crazy too.

[Hector]

this is with the hole in the t-stat. Sometimes I find that even after I have driven the car for a few minutes that some steam still comes out of the bleeder hole. I believe the temperature of the upper rad hose coming off the thermostat should read near 80 C. If you, or a friend, or your indy has a handheld sensor probe you can measure this, with the engine still running, by pointing or enveloping the hose with this sensor. Then you can tell if the cooling system is working adequately.

[Mr. BILL]

Bruno, I filled it the way you suggested the last two times. I was able to get the air out easily with your method. When I open the bleeder screw after warm, only a steady stream of coolant comes out. I am getting ample heat out of the heater too.

I just tried again, and noticed the top of the radiator, where the hose connects is very warm, about the same as the engine, (by feel). However, touching the top of the radiator just 8-10 inches going tword the opposite end, it's cool, almost cold by the time you get to the end. Further, the actial surface of the radiator, with the exception of the area close to the top hose is cool. So that goes with what you're saying about the fan clutch not locking up. The lower partof the radiator, where the lower hose conects is cold.

Does it sound like the radiator is bad then?

BTW, you're sight is a life saver. THANK YOU!

[Brandon J]

You most likely still have air trapped. One method I learned to help get air out is to burp the hoses. What you do is squeeze the hoses a few times. You can do both the upper and lower ones. And then repeat if necessary. Sometimes relying on just heating and cooling does not push the air out. Just like how tapping on calipers to get stuck air bubbles from the brake calipers help, burping or squeezing the hoses a few times helps too. Then see if coolant comes out of the bleed screw. Remember you want coolant to come out of the bleed screw, that means there is coolant in the whole system.


Good Luck

[Mr. BILL]

No, the head that came off the car suffered a broken timing belt. The aux fans do come on.
the castong numbers on the heads are as follows:

origional head, (intake side) 24/7 then:1 705 885 (exhaust side) a round stamp with "89" in the center, I think it's a procudtion stamp maybe April

"new head" (Intake side) 8/01 then: 1 705 885 Exhaust side stamped "88"

I was told this was off an '89 325 and would fit. I didn't have it checked as it was to have been rebuilt and looked as new. The gut I got it from gave me his name and number, so I figured he wasn't trying to rip me off.


Does BMW have a crosss index that'll verify this head will work?

[632 Regal]

same head casting, just different times and dates.

I remember someone mentioning that when they bleed theirs they would put the front on ramps and got it to bleed a lot better.

Now my turn to ask stupid questions that I hope someone can verify.

are there waterpumps that have reverse rotation for these engines, and if so would it be possible to bolt it on?

is it possible to use another head gasket that is not comperable with this particular head/engine perhaps blocking coolant flow?

Besides a leaking cylinder (bad gasket syndrome) im running out of clues except the above questions.

[632 Regal]

it sounds like coolant is flowing to the radiator since it gets as warm as the engine. It will cool quickly once its in there.

did you change the temp sensor yet?


I just tried again, and noticed the top of the radiator, where the hose connects is very warm, about the same as the engine, (by feel). However, touching the top of the radiator just 8-10 inches going tword the opposite end, it's cool, almost cold by the time you get to the end. Further, the actial surface of the radiator, with the exception of the area close to the top hose is cool. So that goes with what you're saying about the fan clutch not locking up. The lower partof the radiator, where the lower hose conects is cold.

Does it sound like the radiator is bad then?

[Bruno]

325i and 525i shared the same M20 engine so I would guess that the head was ok (as long as it isn't cracked and had been pressure tested).

If the system has been bled perfectly (with the heater on). And if when you put the heater on and the car overheats there is NO HOT AIR coming out.

Then I think it is time for a cylinder leak down test. It would seem that one of the cylinders is pressurizing the cooling system (happened on my race car) and the car overheats like crazy (1/2 my radiator was cold also)...

Sorry about all the trouble you have...


No, the head that came off the car suffered a broken timing belt. The aux fans do come on.
the castong numbers on the heads are as follows:

origional head, (intake side) 24/7 then:1 705 885 (exhaust side) a round stamp with "89" in the center, I think it's a procudtion stamp maybe April

"new head" (Intake side) 8/01 then: 1 705 885 Exhaust side stamped "88"

I was told this was off an '89 325 and would fit. I didn't have it checked as it was to have been rebuilt and looked as new. The gut I got it from gave me his name and number, so I figured he wasn't trying to rip me off.


Does BMW have a crosss index that'll verify this head will work?

[Mr. BILL]

well, when I open the bleed screw after warm up and a short drive, a small staedy "gusher" of coolant comes out. Absolutely no bubbles.

[Mr. BILL]

I have it on a sloping driveway and on ramps. If I was sold the wrong headgasket, I'll be pissed!

[Mr. BILL]

Here's how I filled/bled the system. Heat on high, car on ramps, open bleeder on t-stat cover. Filled until steady stream out of bleeder, blow into rad neck until no air escapes, closed bleeder. Opened radiator bleeder,filled until steady stream out of bleeder, blow into rad neck, close bleeder, tighten rad cap.

Start engine, heat on full blast. Let temp com up, open rad bleeder. BTW,with the "blow" methed, very little air bubbles come out. Let run 5-6 min. Take for a spin around block. By the time I get back, temp is coming up to 3/4. Open bleeder on radiator, nothing but steady stream of coolant, rev engine to 2K, same results. Tighten bleeder.

Bang head against wall, curse and throw tools. Run to computer and beg for help on bimmerinfo.

.

[Jose]

Did you actually connect the water hose for the heating correctly on the back of the cilinderhead and the thermostat housing correctly ? Maybe you switched the upper and lower hose on the heater connector pipes. This causes the water to run the wrong way into the heater and builds up resistance causing the temperature to rise and the heater not putting out enough heat to your windshield due to the restricted flow on the back of the head.

If this isn't the case, and you already switched thermostats, checked the tension on your fan belt and your pump is working ok, then I'm afraid it's gonna be the wrong headgasket with too small run through holes for the coolant. ( I suppose you ordered the new gasket at your local dealer ?)

Good luck mate.

[Dan in NZ]

Could be a blocked radiator. If it took 10mins to drain the radiator with both hoses removed, it would seem to me that there's a blockage in there. I recently had an overheating problem only under light load and low speed, it turned out to be a blocked radiator.

I don't know the correct procedure for testing if a radiator is blocked.

[632 Regal]

check the hoses routing as mentioned. That was a valid point I guess (now).

do you have the receipt and or package for the head gasket for part numbers? lets see if you have the correct head gasket. Perhaps compare to old gasket numbers. Lets rule this out or question it.

Leaky gasket as Bruno said? I wouldnt completley rule this out yet because you are having the same symptoms as a blown head gasket.

Will it overheat if it is just idling for a LONG time?

leading to...

does it only go up under load such as driving?

[632 Regal]

this is with the hole in the t-stat. Sometimes I find that even after I have driven the car for a few minutes that some steam still comes out of the bleeder hole. I believe the temperature of the upper rad hose coming off the thermostat should read near 80 C. If you, or a friend, or your indy has a handheld sensor probe you can measure this, with the engine still running, by pointing or enveloping the hose with this sensor. Then you can tell if the cooling system is working adequately.

[Mr Project]

Yeah, just catching up here, but there are several key signs that this is a clogged radiator!

1 - "I disconnected the hoses and it was like peeing...10 mins" If you disconnect the lower hose the radiator should drain dry like a fire hydrant in about 10 seconds!

2 - "Lower hose cold" The lower hose should be cooler than the upper, but not cold. It should still be quite warm to the touch. No radiator is that efficient! :)

3 - "portions of radiator cold" This is a slam dunk. The rad should be warmer at the top then the bottom, but it should be consistant L-R and gradually cooler T-B.

Call BMA!

[632 Regal]

he says it didnt overheat before the head swap

[Mr Project]

Could've finally filled up with oily goop when the HG went, necessitating the swap. :shrug:

[Mr. BILL]

I've been back and forthe on this today. I thought like you, that when I disconnected the bottom hos, is should empty in a hurry. I farted around today and didn't take the radiator to a shop to have it flow tested. Now I wish I had.

[Mr. BILL]

I think I'll pull the radiator and have it flow checked. If that aint it, I give up. I'll have it towed to my indi buddy and let him sort it out.

Thank you all for taking the time to offer help. This place is awsome!

[Bruno]

You can still do a leak down test if the rad isn't the problem.
That will tell you if air is escaping from the cylinders to the cooling system.



I think I'll pull the radiator and have it flow checked. If that aint it, I give up. I'll have it towed to my indi buddy and let him sort it out.

Thank you all for taking the time to offer help. This place is awsome!

[Mr. BILL]

Will do, Thanks much!