nuszmd

After a few months of work, I now have a new motor installed and running after the last one went south. It is running good, oil pressure is good - so I think I got a decent used early motor. The car is an early '85. Motor came from an '83 with about 80k miles (supposedly).

A couple questions that I thought you guys might be able to help with. I've been searching the archives all morning....

Not sure that coolant is circulating, or that it is truly going through the thermostat and into the radiator. The bottom radiator hose was kinda cool to the touch after running the motor for about 15 mins. Top hoses are hot. Fans are running. Thermostat is new, water pump is new. The cooling system worked fine before the new engine went in.

I bled the system with front end slightly elevated - ran coolant all over the place. Still not sure that all the air is out though. Heater did finally blow hot air, but it took quite a while.

Other issue is an intermittent tachometer. Doesn't work when initially started, but starts working after revving the engine and then continues to work fine.

Other than these two issues, everything seems to be in order. I replaced just about every seal and gasket on the engine, so it looks like I won't have any more oil leaks for a long time to come.

Any help would be appreciated - especially on this coolant system thing.

StoogeMoe

The fact that you had problems with the heater indicates that you have air in the system. That should work even if your thermostat is bad. Re-bleed and try again. Make sure you have the heat full on.

If that doesn't solve it, it is not uncommon for a new thermostat to be bad. I had one when I rebuilt my motor. Just don't be impatient and overheat the motor. Keep an eye on the temp gauge.

fbgh2o

Had a bad experience with t-stats as well. Finally ended up running without one.

That being said, I would re-bleed using a pressure tester and the front end as high in the air as possible in the air.

Another thought, how is the radiator could it be a flow problem?

nuszmd

This is all good advice. I am leaning toward a bad t-stat right now, but I am definitely going to try bleeding one more time at least before I start to tear in to get that t-stat out of there. I had the nose elevated some last time around, but I can definitely get it higher. I'll try that, too.

Can I get a new t-stat to fit these cars at any auto parts store? I have been ordering everything, and don't want to have to wait several days again. I must have put at least 10 orders in over the past few months to get parts for this engine.

fbgh2o, the radiator is probably old. I haven't had the car that long, but I went with the same radiator that was in the car before I jerked out the motor. It worked before I had the car sitting these past three months. I don't think I am getting any flow through the radiator right now, so that's why I am leaning toward the t-stat. I'll probably start questioning whether I have a good water pump (rebuilt) next, but maybe I need to consider the radiator as well before I really start tearing the car apart to get to the water pump.

Thx for the help!

nuszmd

Man, screwing around with the coolant system all day and it's not getting any better. In fact, I think it is getting worse. I think I might have blown a seal on the water pump - or at least I hope this is what it is and not a head gasket leak. I didn't overheat the car, so I am thinking that it was a weak point in the gasket sealer I used to seal the water pump gasket to the block.

Anyway, I went out and picked up a pressure tester from AutoZone. The radiator cap tested good. I put it on the reservoir, and pumped it up to about 3 or 4 lbs and started noticing leakage from around the oil cooler. Further investigation and I was able to narrow it down above the oil cooler, in the front of the motor, behind the belt cover. I don't think it is a hose leak. I can't see in there, so I'll be digging into the belts tomorrow....

All this from a thermostat that won't open. I still don't think that thing opened at all today in my multiple attempts to bleed the system. I guess I'll be checking to see whether or not the new (rebuilt) water pump is any good while I'm in there. And that thermostat is coming out for another new one. What a PITA.

Will probably be another week to get it on the road again.... @#$%!

Any advice before I rip into the car tomorrow?

Landseer

Well, you would think the radiator would be ok. You are going to have to drain it at this point, I think, anyway, and can run a hose through it to make sure you have flow. I assume you can feel it starting to really heat up, so you know its not a bad sensor reading weird on the dash. I bet its something else though.

If I were you, I would take a hard look at the water pump and thermostat, especially if it was from the newly acquired engine. Is it recent? Did you put it on the replacement motor yourself? Its a hell of a lot easier to replace the thermostat with it out, and I have other reasons that you need to be able to look down that passage behind the tstat and you can't do it in the car.

The water pumps, like the 928 waterpumps, have some design deficiencies such that rebuilds sometimes fail with impeller slipping on shaft, sometimes as new rebuilds. (just an interference fit, there are some bad china copies out there with poor shaft tolerances, the tolerances of the shafts are getting worse with multiple rebuilds of the same recycled pump...lots of reasons... and we are trying to find custom builders that will upgrade them for us.... I digress ). They reportedly have a weak, fairly rudimentary packing seal as well and often fail after sitting and being brought back into service if they were run for a while, then sat in the car.

At the same time, the thermostat, like on the sister 928 engines, enables a more complicated cooling path than on a GM type car. The thermostat, when open, is actually also closed. What I mean is it opens to allow water to circulate into the radiator, but it must open all the way ---- and when it does, the back part of the thermostat seals against the rubber seal that is behind it. If this doesn't happen, too much coolant will still bypass the radiator and go through its orginal path. Thats why 944's and 928's run hot (in case of 928, boil over) when the seal behind the thermostat is degrades (lots of folks don't know its there). Same thing if you run one without the Tstat -- runs hotter.

I just did three 928 WP's and followed it up with a 944 pump to make the comparison. Same set-up, except the seal behind the Tstat came already installed inside the particular rebuilt 944 pump that I put in, right behind where the thermostat mounts. (It comes as a separate part number and is mounted in a different place on the 928, but same concept, right beind the thermostat).

Though I dug into the 944 for a TB / pulley squalling problem, my son had reported creeping high temps, gauge running higher than he was comfortable with. I replace the WP, TS, and saw the good new seal in the rebuilt WP.. Sure enough, its running much cooler now all the time. Saw remnants of a badly degraded seal in the old pump. Solved it.

So, a partially or non-opening Tstat hurts your temp. One that opens properly, but against a degraded or nonexistant rubber seal in the WP also hurts your temp. And the seal leak and possibly impeller slipping is also a potential problem.

It is not unheard of for owners to dump entire automobiles, thinking they have a headgasket problem and trying to avoid the bill. Great way to buy a good car cheaply !!!

Now, the odd thing is that neither Clark's garage, nor most of the rennlist DIY discussion call this out. But I found one ref, below. Same with 928 guys, lots miss this seal-behind-the-tstat.

If anybody has counter-information---- please post it --- as if somehow I am wrong on the 944 we need to drive a stake through my response --- we need to keep wrong information it its place ! But I think I am right.



(The thread referenced below has some speculative blab in it, but checkout the important post #14 by "Oddjob" within this link as partial validation of the stuff I've posted above)

https://rennlist.com/forums/924-931-...you-think.html

nuszmd

Good info. I don't recall seeing another seal inside the water pump behind the t-stat. I put in a new (rebuilt) water pump that I ordered from Zim's (I think). Also a new t-stat, with a new rubber o-ring seal that wraps around the t-stat. Also ordered a new snap ring because the one that came out of the old motor's water pump was broken in half. I am going to get the water pump back out and re-install it with new gasket and new gasket sealer. I am hoping to be able to narrow down that the leak was in fact coming from the water pump and not the head gasket. While I have it out, I will look for the seal that you are talking about. I'll get a new t-stat, and I think I'll go back to the mid-temp range t-stat. I had installed a t-stat for cold weather operation last time around.

Question: How can I determine whether or not the impeller is spinning properly on it's shaft? I still haven't been able to determine whether or not the water pump is actually functioning properly.

I'll also run some water through the radiator while I have it drained. I should have done that prior to re-installing it.

I should buy stock in an anti-freeze company the way I am going through jugs of new anti-freeze.

Landseer - Thanks for the info. This is helpful. I read the other thread about the bypass path for the coolant and it makes sense to me.

Edit: I just remembered that the t-stat came with two rubber round o-ring seals with a groove inside of the ring. They were similar, with one being a little thicker than the other one. I just thought that they were both for the t-stat and you just use the one that fits the t-stat and the water pump best. I chose the thicker one and did not use the other one. Could this be the other seal that you are talking about?

V2Rocket

im not quite sure i understand your logic - at first glance it seems you are saying that the t-stat opens to allow water from the block into the radiator. water flows from the head to the top of the radiator and cools as it goes to the bottom, then the waterpump sucks it into the block.

actually now that i think of it the tstat would have to be open to let water to continue circulating.

Landseer

Nuszmd, not sure, very possibly. The question I raised is fundamental, so maybe these 944 guys with some experience will weigh-in. I'd hate for you to dissasemble on my accord.

Hi V2,

I'm pretty sure it is a forced bypass thru block w/ thermostat closed, WP driving the circ.
Then, when Tstat opens, it goes thru radiator.

However, the way these are set-up, the path of least resistance is thru block, so it does both if Tstat doesn't seal against the back passage completely, water goes both ways, some effectively bypassing the radiator, causing higher temps. Lets check my hypothesis, I think its right. Who are the real wrenches on 944's we can ask? Youv'e been here for 11,000 posts, help us check it.

BTW, fron UC Riverside, us old guys do expect some hit it posts....

V2Rocket

im not sure i understand what you mean by "bypassing the radiator".

from when i rebuilt my engine (mind you, almost 3 years ago so knowledge is a bit fuzzy) i recall that the way the cooling system on the 944 is designed, the water gets pulled by the waterpump from the bottom of the radiator (the coldest part of the radiator) through the block, around the cylinders, and then it gets flowed through the head and out to the top of the radiator. the thermostat "closes" and restricts waterflow but still allows some trickle. water is always in circulation through the engine no matter what the engine temperature. this allows for a slower flow of water which lets the engine warm up faster on cold starts.


as for "hit it" do you mean the thread in OT? ive made contributions there but none of my UCR conquests. i dont have a camera besides the one on my phone, but ill work on it.

Landseer

That is also what I recall. Further, I'm pretty sure that the moving metal disc within the tstat is supposed to bump against a rubber seal mounted in the throat of the water pump to restrict that flowpath, ie, restrict the amount of flow goes through the block without going through the radiator.

Let's see if we can confirm the necessity of the seal.

V2Rocket

as for the presence of the seal id rather not pull my car apart just yet, though it may be time to do that soon..

also here in san diego right now its raining which is basically freak weather and im nice and warm and cozy

the tstat, when cold, certainly restricts waterflow but water is always flowing, even in a smaller amount. it does go through the radiator no matter what though, there is nowhere else for the water to run.

nuszmd

OK, so far I think I am doing ok on the refilled radiator/engine coolant. I tore into the motor, and found that what I thought was a leaking water pump was really a leaky upper radiator - head hose. Tightened that up, and haven't had a leak yet.

Moral here - check and re-check your hoses before determining that the leak is coming from somewhere else. Would have saved me a lot of time as I basically removed everything to replace the timing belt and water pump. Lot's of wasted effort here.

I also replaced the new thermostat with another new one. That seemed to take care of the problem with overheating.

Also, the use of the pressure tester really helped to bleed the system. I went to AutoZone and borrowed the tester. It hooked right up to the expansion tank without any kind of adapter. With the engine cold and the heater control fully open to hot, I filled the expansion tank up - with the bleeder valve open at the top of the radiator/head hose connection. I left the screw in place so that when it did bleed, it only spilled a small amount of fluid. Then I hooked up the pressure tester and pumped it a few times to get the fluid pushed up into the motor. Push slowly so that most of it goes into the motor and doesn't slosh out the bleeder valve. Pump until the expansion tank is about empty. Then I just continue this process - fill tank, compress, etc. until I was getting pure antifreeze coming out of the bleeder valve at which time I closed the valve, topped off the tank, and shut the expansion tank cap. I did all of this with the front of the car on jack stands. So far, it is running good and temp is hovering about mid point all the time.

Since I didn't take the waterpump out, I didn't check for the other seal in the pump as described in the thread above.

Also, I was having a bunch of trouble getting the snap-ring out of the water pump until I went to sears and picked up the snap-ring tool with multiple attachments. I used the 45 deg attachment and it was pretty simple to get it out / started. Used a long screwdriver to get it all the way out after disengaging it from the groove with the pliers.

F18Rep

Typical. BTDT.