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 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!