[Cloud9...68]

I've been hesitant to post another thread on this, because I'm afraid of what the answer be, but I'm beginning to resign myself to it. For over a year now, my car has been running hotter than it did in the first few years I owned, and I believe hotter than it should. I've replaced numerous thermostats, and most recently installed one from RS Barn, into which they drilled a half-dozen small holes near its periphery to allow a small amount of coolant to flow past at all times, to allow more gradual warming of the engine. I simultaneously replaced the coolant reservoir cap with one from RS Barn. The car doesn't consume a dop of coolant, and I've recently bled the system when I replaced the latest thermostat. The fans work perfectly - both come on at their relative prescribed cues, and they both blow up a storm. I've had oil analyses done as part of my last two oil changes, and neither showed even a hint of a trace of ethelyne glocol. I taken the radiator to a shop to have it cleaned out (though they told me it was perfectly clean and free of any obstructions of any kind when I brought it to them).

It gets particularly hot when I drive it aggressively - one trip to the redline, and the temperature gauge is close to the 10:00 oclock position (upper line on the gauge), though when I ease up, it drops back to where the needle is slightly above the 8:00 oclock line. Driving around town, even on a hot day, in traffic, and it stays at 9:00 oclock or slightly below. When I first got the car, I swear it never got above 8:00 oclock, even during aggressive driving. Buyt even on the coldest of days (below 30 degrees F), it never stays below the 8:00 oclock line, which seems very odd.

What concerns me is that after the engine is fully warmed up, the fat radiator return hose (on the passenger side) never feels very warm, which tells me (I think) that I'm not getting enough coolant circulation. I wish there was another 968 nearby I could compare my by-feel radiator hose temperature to, but the other one is much hottr than the fat one on the passenger side, which doesn't seem right. .

This brings me to the part I'm dreading. I replaced the water pump as part of my belt change two years ago with a remanufactured one from Paragon. Soon after installing it, the car was running hot, which did turn out to be a bad thermostat, but in the course of troubleshooting the problem, I removed the water pump to make sure the impeller wasn't free-wheeling on its shaft, and it wasn't - couldn't have been any tighter. I even put the water pump in a large pot of boiling water and tested the tightness of the impeller at close to operating temperature, and it was fine. Once I got a good thermostat in there, it ran fine, even at the track on some pretty hot days.

Based on my current symptoms, do you guys think the water pump could have failed? It's definitely not leaking, and it's such a simple device that I can't think of another failure mode that could explain the apparent lack of proper circulation other than a slipping impeller, which I suppose could have worked its way loose over the past couple of years. Can anyone think of anything else I should check before resigning myself to putting in a new water pump (when I rebuild the head, hopefully later this year)? Thanks.

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[unknown4u]

is the automatic tensioner working correctly from the main belt?.
If th tensioner does not work properly the pump won't spin and you have the symtoms as you describe. Check the tension when the engine is hot and cold.

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[Cloud9...68]

I replaced the tensioner two years ago when I replaced my belts, but this doesn't mean it couldn't have failed. How would I check it? By taking the belt cover off and seeing if there is any slack in the main belt? Thanks for the suggestion - this is something I hadn't thought of.

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[Ryan]

If I read this correctly, you put in a new thermostat after the new pump and all was well for a while? If this is the case, I would put in yet another thermo or pull it out and run without to see if it solves the problem. It sounds like a bad pump or thermostat.

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[Johannvb]

I support Ryan's advice.

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[Chris Vais]

I concur with Ryan as well. It used to be that when a thermostat failed it was designed to fail in the full open position. Well, it turns out that isn't always the case. A collegue at work suffered a huge engine overheat that resulted in a blown head gasket because the theromstat failed in the closed position. I don't know whether our thermostats fail closed or open.

Run it without the thermostat in place and see if that solves the problem, if it doesn't, check the tensioner. When my water pump failed the first time, it began with car gradually running hotter until it got to a point where the pump was not circulating any water at all and we would be in the red zone immediately. The failure was the impeller breaking down to the point where it cavitated rather than pumped water and it never leaked.

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[Cloud9...68]

Well, I'm on about my fifth thermostat, the current one being from RS Barn. I know these things fail from time to time, but I'm having a hard time swallowing that I have yet another bad one, brand new out of the box, as much as I'd like to believe the problem is as simple and cheap to fix as that. Especially since this one is drilled, which should allow at least some coolant to flow. But if is the thermosat, which means every one I've bought for the past three years has been bad, what are the chances of getting a good one?

As far as the belt theory, I checked my balance shaft belt tension a few months ago, and while I was in there, for some reason I checked to see how tight the timing belt was by trying to turn the water pump by hand. It didn't budge. Which isn't to say the tensioner couldn't have failed since then, but it's been running hot like this for many months, so it thi ha been caused by a loose timing belt, wouldn't this have caused a major catastrophe by now, one involving a bunch of bent valves and broken pistons?

I guess the most sensible thing from a diagnostic standpoint would be to try running it without the thermostat. If this fixes it, I'm inclined to leave the damn thing out and never install one again!

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[flash]

take the chip out and replace it with the stock chip and see if that fixes it

what i suspect is that you have a heavily carboned engine, and the racer x chip is over-advancing given the carbon - this would cause detonation under load, as the racer x chip has a LOT of timing advance

while you are at it, i'd also check your ECU number - the early ones have the wrong ECU, and only weltmeister and autothority ever made a chip for the early ECU

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[Cloud9...68]

That's an interesting, outside-the-box theory, which I really appreciate. I want to rule out every possible option before replacing the water pump, as I have a gut feeling, though totally unprovable, that it isn't the pump.

I kind of doubt I have a heavily carboned engine, though, based on the fact that I had the Run-Rite treatment performed about a year ago, and very little black smoke came out the tailpipe during the treatment. I also add fuel system cleaner with every fill-up, so I'm pretty anal about at least trying to keep my engine's insides clean. Also, if I had heavy carbon build-up, wouldn't I be seeing some artificially high compression numbers, not to mention some soot build-up around the tailpipe? My compression numbers are all in the low-to-mid 170's, the car has never smoked, and the tailpipe is pretty clean for an 18-year-old car.

My number one concern is with the fact that the return radiator hose isn't getting warm, indicating I have a water circulation problem (right? If someone could please check how hot theirs gets after the engine is fully warmed up, I'd really appreciate it). It seems like this says thermostat, water pump, a huge air pocket, a clogged radiator, or a loose timing belt. Unfortunately (or fortunately, as the case may be), I can make arguments of varying degrees of credibility against each of these.

Here's a quick summary of my symptoms:

- Gets very hot very quickly under load (heavy acceleration), even when it's not terribly warm outside
- Never runs below the 8:00 oclock line, even under very gentle driving in 30-degree temperatures (about as cold as it ever gets around here)
- Under normal, non-agressive driving, on a hot day it doesn't get above 9:00 oclock, so it doesn't seem to be in danger of actually overheating.
- My recollection is that once upon a time, it used to stay at the bottom line under these conditions
- Return radiator hose never warms up; I can grab it without the slightest discomfort
- The upper hose, on the other hand, is, as expected, blazing hot - way too hot to touch

By the way, I hope nobody takes my "arguments" against their theories personally. I REALLY appreciate everybody's inputs; I'm just trying to reason my way through this thing as much as possible before turning any wrenches. Thanks again.

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[flash]

ok - if the hose is not getting hot, coolant is not circulating - this indicates either a major blockage, a failed thermostat, or a failed waterpump

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[Cloud9...68]

Yep - that's what I'm afraid of. I suppose the surest way to narrow it down is by removing the thermostat, though I recognize this isn't a good way to drive the car long term, because of the excessive "washing" of the cylinder walls that would result from running too cold for too long (provided the thermostat I remove was bad, resulting in the return of proper circulation). But as a diagnostic, it will help narrow down the source of the problem.

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[rxter]

Disclaimer - I am not a mechanic. But I need to challenge the basic logic of the non-circulating coolant theory

You run between 8:00 and 9:00 under normal, non-aggressive driving with no danger of overheating. If you had no coolant circulation wouldn't you run hot after the friction of the engine heated everything up and always run the risk of dangerous overheating? How could it cool back down if the coolant is not circulating?

Using the temp gauge as your measuring stick, your situation doesn't sound all that different from what I have seen in a couple of these cars.

"It gets particularly hot when I drive it aggressively - one trip to the redline, and the temperature gauge is close to the 10:00 oclock position (upper line on the gauge), though when I ease up, it drops back to where the needle is slightly above the 8:00 oclock line. Driving around town, even on a hot day, in traffic, and it stays at 9:00 oclock or slightly below."

Your description is pretty much what I see from these cars all the time. When I hammer it on a warm day the temp gauge jumps, but then comes back down if I give her some air.

I can't reconcile this with you not feeling a hot radiator return hose, but your symptoms don't sound like anything is really out of the ordinary, at least for this car - the temp gauge jumps more than other cars I've seen. Any chance that it is calibrated to show smaller differences than other cars?

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[Johannvb]

What is the possibility that you temp gauge is over sensitive? WIth this I mean that the gauge exagurates the temperature variance, so for example that instead of 8 o'clock and 10 o'colck having 10 degrees difference it has 2.

I have no idea what the temp range of the gauge should be, but it seems to me like it is something worht checking out.

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[John]

Cloud..., I think you might be able to tell if the pump is working.
There's a constant but small volume circulation path that leaves the head from the elbow at the front of the engine, goes into the radiator top, comes back out the radiator top through the smaller hose into the rear of the expansion tank, and from the tank goes to the smaller pump inlet, thus bypassing the thermostat through some pathway internal to the pump.
With the heater off and a cold engine, you should see a modest flow of coolant running into the expansion tank. You might see it through the side of the tank, or you may need to take the cap off to see it.
This is how mine behaves anyway, so maybe worth a look. ... John

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[flash]

i think the first thing to do is take real measurements of the temp

then flow needs to be verified - this will be a messy job, but very brief - pull the return hose, connect a length of hose from the fitting on the engine to a bucket, then fire it up and watch what happens - if the pump is turning, there will be a LOT of coolant exiting - if it isn't there will only be a little bit

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[Cloud9...68]

As usual, I'm gratified by the volume and quality of the suggestions. To respond to a few of them, I'm pretty convinced something has changed, because my car used to hold at the bottom line, even in very hot weather. And the sudden rise as a result of just one quick burst of acceleration is way different from how it used to behave. I'm sure it would overheat after a couple of laps at the track. I suppose it is possible that the guage has gone south, but I keep going back to the fact that the return hose is cool, which just seems so wrong, even though the return water has been cooled as a result of just having exited the radiator.

John - I'll definitely try your suggestion as soon as my car cools off; I just got back from driving it.

The bottom line to me is the coolness of the return hose. I wish I knew of another 968 in Austin I could compare mine to. Again, could I please get somebody to put their hand on the return hose after their engine is fully warmed up? Be careful not to get your fingers caught in the fan! Thanks.

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[flash]

take measurements

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[Cloud9...68]

"take measurements"

What's the best way to do that?

Another tidbit, that seems to answer my own question about the proper temperature of the return hose: After my belt/water pump replacement two years ago, when my car was exhibiting similar symptoms as it is today, I remembered the previous owner telling me he had installed a low temp fan switch. So I replaced the thermostat with one advertised to open at 165 degrees, and bingo, problem solved. The car ran cool (at least for awhile), and I remember the return hose getting good and hot. But I'd still like to see if others' return hoses also get hot, just for corroboration.

So, I'm wondering if my low temp fan switch is contributing to my problems. In checking the apparent direction of coolant flow, it looks like the pump pushes the water through the block and head, then into the radiator, out the fat return hose, and then against the thermostat. If the water has cooled excessively (due to the fans coming on at an abnormally low temperature), and the thermostat is set to open at too high of a temperature relative to the temperature that activates the fans, won't this make it difficult for the thermostat to open? In other words, don't I need a low-temperature thermostat to match my low temperature fan switch? The one I have in there now is spec'd to open at 172 degrees.

I'll do some checks this weekend, starting with he easiest, and working my way to the harder, and messier ones.

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[flash]

get a laser thermometer - you can pick them up for less than $100 - great for tire temps too

the low temp dual speed switch turns the low speed fan on at 185 (85C) - the stock fan switch turns them on at 198 (92C)

the stock thermostat is fully open at 181 (83C) - there is a low temp thermostat at 160 (71C) , and another one at 180 (82C), but i am unaware of one at 172 (78C) - i looked for that one, but could not find it - neither could pete

i wondered about running a low temp thermostat myself, and decided against it, as gasoline engines run best when at a coolant temp of between 190 and 195 (though emissions are lower f it is a touch higher) - i felt from my experience that a 160 would be too low

thermostats are not on/off switches - they open gradually, beginning at a temp a bit below their set point, and constantly open and close a bit at a time as the temp fluctuates

i highly doubt it is your thermostat - sorry

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[Cloud9...68]

Thanks for the info. I may not be remembering correctly, but I thought Max said the one he sold me opened at 172.

I don't have a solid argument for thinking it's somehow related to the thermostat, other than:

1) I had very similar symptoms a couple of years ago, which were cured (or admittedly possibly only temporarily masked) by a new, low temp thermostat. I didn't immediately suspect this this time around, because the current t-stat is brand new. And

2) If it were the water pump, wouldn't the symptoms be getting worse over time? In other words, if the impeller were starting to slip on its shaft, wouldn't it eventually start free-wheeling, stopping water flow altogether, and causing massive overheating? My symptoms have been very consistent for many months, which is why I haven't had a huge sense of urgency to fix it. But with summer looming, I know it's time to get to the bottom of this.

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