I replaced the Thermostat in my car this weekend (an adventure unto itself). I ran into a problem replacing the driver’s side bolt for the housing - it wouldn’t screw far enough in to seal the housing and compress the gasket. It didn’t seem to be cross-threading; it just stopped about 1/2" too soon. Taking the advice of a friend who’s worked on his own cars for years, I replaced that bolt with a shorter one that tightened enough to seal the housing.
Things seemed pretty good for a couple days; though the car ran warmer than I thought it should, it was nowhere near overheating and it wasn’t leaking any coolant. However, the temp gauge reading fluctuates a lot - if we say there are ten reference markings (0 being cold and 10 being red-line hot), the gauge will fluctuate between 2.5 and 8.5, where in the past, the reading was at 2.5-3 and didn’t move noticeably.
And, to make this more interesting, it seems that after a certain amount of driving (the time required seems to vary), the cooling system “settles in” and the gauge will go to the 2.5 to 3 mark and stay there (as it should).
I’ve checked the coolant levels and they’re good (still no leaking or loss of coolant). No coolant in the oil. I don’t think I’ve got any air in the cooling system, but I can’t say for certain - I was told to get rid of any air pockets to run the engine at idle with the radiator cap off, which I’ve done. I didn’t flush the coolant when I changed the t-stat, but it’s not very old (about 6 months) and is still clean looking.
I’m not much of a mechanic, so saying this has stumped me isn’t saying a lot, but I’m stumped. Can anyone offer any advice?
If it makes a difference, my car is a 1993 Thunderbird SC with a manual transmission.
Try putting a different thermostat in, try the stat for a turbo charged 3.8. Also, check for air getting into the cooling system, check the radiator cap to make sure it is working properly. Also, check the water pump impeller they can corrode away making for insufficient coolant flow. Good luck, I hope you have the 93’ thunderbird auto guide, to find the parts if you are not so familiar with the engine.
You don’t say why you changed the thermostat, but are you sure the replacement one was correct? I can’t understand why you weren’t able to re-use the same mounting bolts. It might be an idea to look at the thermostat again and see if it’s damaged.
Yeah, she’s my dream car. Though it hasn’t been a good dream lately.
I got the thermostat from Ford and it’s the one for the SC (I’m sure that’s what you meant, but Ford didn’t make a 3.8 turbo - the turbo was discontinued after the '88 model and had a 2.2, I think; though carpoint says it had a 2.3 - pointless tangent: I was offered a black one years ago in mint condition and turned it down because I was young and stupid ).
I’m not seeing any leaks around the radiator cap (and I’ve looked at it while the engine was hot as well as cold) - is there something else I should check for ?
Where is the water pump impeller ? Is it part of the water pump itself (which seems to be a real trial to get out).
I don’t have a shop manual (they’re hard to come by), though I’ve meant to for a couple years now). I’ve been going off a Haynes that’s I got from the library.
Sorry - I changed the thermostat because the car was heating up and then cooling (as per the gauge readings) - it was go from cold to hot and back and after a few days of this, it would just stay hot. I opted to replace the thermostat because it was a supposedly cheap and easy repair (HA!) and I figured I could take it to the shop afterwards it that didn’t fix it.
I was puzzled about the mountin bolt as well - it seems to me that if it came out that it should go back in (and, BTW, it’s only the driver’s side bolt that has problems, the passenger side bolt went on without a hitch). It didn’t though and tightened up to where I couldn’t get it in any further. I didn’t want to use a cheater or an air wrench or anything like that because I didn’t need onee to take it out and I was afraid of screwing up the threads in the bolt-hole (I know that’s probably not the right term, but I’m hoping you’ll know what I’m talking about). So I arrived at the shorter-bolt theory, which seems to be ok - the housing appears to have sealed tight.
And the thermostat in it is actually the second I’ve tried - the first was from Advanced Auto, but when I started having problems, I decided (on advice from another SC owner) to go with a Ford t-stat. FWIW, the Ford one is a little smaller, but made no difference to the problem with the bolt.
I’m not even sure that the problem is related to having used a different bolt or to the poblem with getting the factory bolt back in, but I wanted to get all the facts out.
Since things worked normally before the thermostat replacement, we’ll assume that what you’re observing now has been caused by the stat replacement.
That leaves two areas of possibility: parts problem and installation problem. Leaving air in the system is the only plausible installation problem that comes to mind. (In some cars, stats can be installed backwards, but that virtually always results in significant overheating, rather than the fluctuation described.)
It could be a faulty thermostat. Not likely, but not impossible. Check other possibilities first.
Air in the system is the most likely suspect. Idling with the cap off is not a reliable method to get all the air out. That said, the chances of it doing the trick are much improved if the car is jacked up so that the radiator cap is the highest point of the cooling system, and if one watches carefully for the stat to open (indicated by visible flow of coolant across the top of the radiator and/or the coolant level dropping noticeably) and quickly tops up the system and fully installs the cap at that point. Another technique to expel air is to pull off the highest heater hose (cold engine, not running) until coolant runs out of both the hose and the pipe it goes to. Some cars have an air bleed screw somewhere in the system which can also help.
Make sure that the overflow jar, if equipped, is filled to no less than the maximum line. Recheck it after the car has cycled from fully warmed up to fully cold, and if necessary refill it to the proper level.
While I doubt it has any bearing on the problem, it worries me that the bolt wouldn’t thread in all the way. One possible explanation is it was the wrong bolt, somehow getting mixed up with the other bolt or bolts removed to do the job. Another is that there was something else between that bolt and the stat housing, e.g. a bracket, that got left off. About the only other one I can think of is interference in the hole, caused by debris or liquid sitting in there. I’d review the replacement process to see if either of the first two suggestions apply, and if not I’d remove that bolt and carefully clean and inspect the hole. It may not be a big deal, but if the bolt is indeed shorter than it’s meant to be, it might not hold.
Now I see a post where, if I understand correctly, you indicate that the fluctuation preceded the thermostat replacement. If that’s the case, I’d say the problem lies elsewhere. Air in the system is still a possibility, likely due to a leak.
It also occurs to me that the threads on the original bolt may have gotten damaged, although it’s rare for that to result in exactly what you described.
I don’t see that a mix-up with the bolts is possible as there were only two and they’re the same type. I didn’t see anything wrong with the threads on either bolt, but if it’s a subtle thing, I may have missed it (not being any kind of mechanic and all). I can’t get at the hole that is causing problems at there is a doohickey in front of it (don’t know the right name, but it’s basically a wheel on a spring that keeps tension on the belt and taking it off was more of a project than I wanted to get into - see the non-mechanic disclaimer above).
I don’t think the problem with the bolt not going in is with the bolt itself - I tried a different bolt of the same length and diameter and had the same problem, so I’m thiking something’s wrong with the hole.
I’m hoopeful from what you’ve said that there may just be air in the system. I’ve got some ramps at home - I’ll run the car up on them tonight and then see if I can get any more air out.
bauble
[Off on a tangent]
I’d just like to say that before I install a thermostat, I always put it on the stove in water with a candy thermometer. I have caught two brand new defective thermostats this way. Saved a lot of trouble.
[/ooat]
By the way, would the excess length of the bolt be about the same as the thickness of a bracket of some kind? How much shorter did you need?
consider the possibility that the temperature gauge, and not the stat, is the problem.
Next time the temp goes way up, crank up the heat to max and turn the fan all the way up. The temp should drop immediately. If not, suspect the gauge/sensor.
Seeing how the temp was doing the same thing prior to replacing the thermostat as it is now, I think the problem might be elsewhere. While the water pump is a possibility, they don’t usually cycle from working to not working - when they go bad they’re bad and usually leak at the same time. It could be that you have a leaking head gasket.
On a side note, I think I just cooked the engine in our old utility PU truck yesterday when the thermostat stuck. Temp gauge wasn’t working so I didn’t know it was hot till the engine started running funny (combined with the slight coolant smell). Took the thermostat out and got it home, but now it’s blowing oil smoke from the exhaust.
You know, the same friend that reccomended the shorter bolt, also had me do this. I’d neveer heard of doing it before, but it made so much sense, I don’t know why it isn’t part of the standard instructions for changing a thermostat.
The bolt I ended up ising is about half an inch shorter than the original. I thought about the possibility of a bracket, and since I can’t actually see where this bolt goes in, I can’t rule it out, but the Haynes manual doesn’ show one and I can’t feel one.
I’ll try that tonight. I’m wondering how much good it will do, though as so far there doesn’t seem to be any correlation between either speed or rpms and the temp (I’d have thought that if hte fan was out, the car would run cooler on the highway than standing still or that if the problem was with the water pump that running the engine harder would cause it to run hotter, but neither of these is the case).
Man, I really hope you’re wrong here (no offense). I can’t replace either a water pump or a head gasket myself, but I know that having the headgasket replaced will run me around $1200 (and that having the water pump replaced would be a lot cheaper). I’ve checked a couple of times and still don’t see any coolant in the oil - I know that coolant in the oil is pretty reliable indicator of a blown HG, is the reverse also true (no coolant in the oil=no blown HG) ?
Foamy residue on the inside of the oil filler cap is a good indicator of coolant in the oil.
When the temp gauge is showing that the engine is running hot, does it seem to be the case when you open the hood? Strong coolant smells, leaks, high coolant reservior level, etc.
No coolant smell (well, not anymore - I spilled a fair amount while working on the car, but that’s cleared out) no leaks that I can see. The resevoir level insn’t high, though it doesn’t seem to change much from cold to hot.
tadc might well have a point in questioning the reliability of the temp gauge. Might also be the sending unit instead of the gauge…
If the engine is indeed overheating it would have to be either something coolant related:
poor circulation due to water pump
bad thermostat preventing proper circulation
plugged radiator preventing proper circulation
OR
bad head gasket
Well, I talked to my mechanic (a friend who is a real mechanic, as opposed to the many shadetree mechanics I know) and he said that since I don’t see any coolant or “frothiness” in the oil and since there isn’t any smoke in the exhaust and since I’m not “missing” any coolant (dont have any unaccounted-for leaks) that he doubts that it’s a blown head gasket (though, of course, he couldn’t say for certain without looking at the car).
I hadn’t considered that the radiator (or, presumably, one of the hoses) might be clogged.
I’m hoping that it’s somethin to do with the coolant or the circulation thereof, just because that doesn’t sound nearly as scary as a head gasket replacement.