speshalK7

I'm having some strange overheating problems with a recently acquired 1991 Prelude, 173000 miles. the car will perform normally in city driving and short trips, but when I drive on the freeway for about fifteen minutes going about 80 the engine temp will begin to rise. The strange thing is, that the only thing that seems to affect it is if i put the car in neutral and coast for about 20 seconds, and then either rev the engine or put it back in gear and the temperature will go back down! also the amount that it goes down seems to be tied to the length of time that I coast; longer coast=more temp reduction. This will work for maybe another 7-10 minutes before the temperature rises again, and I have to repeat the process to make it to my destination. using the heater on full blast will prevent this from happening as Fast, and makes the coasting/cooling process faster, but doesnt remedy the problem. Any ideas?

I've had the car checked at a shop, and they can't seem to find anything wrong. I recently changed the thermostat, and I also flushed the system and made sure about getting 50/50 coolant in there, still no change

--also recently my engine decided not to startup, no turning or anything, and I tried to jump it but it doesnt seem to be tied to the battery. The car had been running fine prior to this, and when it happened I was trying to start the car and the engine turned slowly a few times before giving me nothing at all. Any help with this as well?

Lynxx

I've seen this issue only once before and it turned out to be a half-clogged radiator that was the culprit. It did the same thing yours is doing except that this car would also overheat if stuck in traffic or if it sat too long after driving.
When you flushed your system was the coolant clear and looked to be in good condition or was it cloudy or dark? What I believe happened with the car that I had was that someone tried to use some kind of stop leak but didn't do it properly and so it basically sealed a bunch of the slats in the radiator instead.
I found this out by letting the car warm-up and then gently touching the radiator slats. Some were much, much cooler than the others (the ones that were clogged).
As for the engine not starting, is that where it's at now? It will not start at all? Does the starter click but do nothing else?
The reason I ask is because if the engine has been getting hot it is possible that you've blown a head gasket and filled a cylinder with coolant (which, since you can't compress water, will cause the engine to seize-up). An easy way to check for this is to pull the spark plugs, examine each (looking for water or coolant), and try spinning the engine over without the plugs.
Hope that's not the case!
Good luck!

speshalK7

Yes as of now it still isnt starting, nothing turning at all. There is a click, but nothing else. If there is fluid in the cylinder, would it attempt to turn at all or is it possible for it to produce nothing? I will check the spark plugs just in case.

As far as the overheating, When I flushed the system, there didnt seem to be any discoloration with the fluid. The strange thing with mine is that it actually works better in traffic or when stopped for an extended period of time. The temperature only becomes a problem when I am driving steady for at least 15 min..

Lynxx

It would do nothing but you would hear the starter click. Basically there's a piston trying to compress the coolant (and that's physically impossible) so it's as if the piston is hitting a wall. Definitely pull the plugs and try spinning the engine over without them installed and see what happens. The gasket could have been the problem all along.
Hope it's not, but if it is then at least the problem is found. Good luck!

mberndt

Considering you took it to a shop, and said that they could find nothing wrong, and barring the possibility that the shop employees are complete idiots, then I don't see how they could have not-diagnosed or mis-diagnosed a common head gasket problem... Besides, you would have noticed the excessive amount of thick white smoke, if you had blown a head gasket... if anyone has ever seen one blow, you know what I am talking about lol...

When was the last time your water pump was replaced? Did they replace it at the recommended interval? it's got 173k miles, and it's a 91, so I figure it should have had at least 2 timing belt changes, along with the recommended water pump replacement. It could be the water pump...

I had my 93 dx for 2 years before I got my swap, back in '00. The timing belt and water pump were replaced at the required interval of ~60k miles. I did not replace it again at ~120k miles because I was waiting to get my swap. Around 125k miles, I experienced the same problem as you describe... Temp would rise, and the only way I could get it to go back down, was to rev the engine up... I assumed this was because the water pump had gone bad, and it was not flowing enough coolant through the motor, until I would rev it up, to get the coolant flowing... Never figured it out, like I said, we tore out the D15 and put in a B16A2... but I always suspected it was the water pump...

it wasn't a head gasket prob, as it didn't burn any coolant...

Hope this helps!

Lynxx

Not to sound rude or confrontational here, but what you need to realize is that a head gasket doesn't just blow-out in a large section all at once... especially with newer vehicles (partly due to the primarily-metallic head gasket as opposed to the older graphite ones). What usually happens is that the gasket loses it's seal due to whatever conditions (stretched bolt, gasket flaw, whatever) in one small section and that section grows -usually pretty rapidly- to become the major problem that you're familiar with (the steam out the exhaust, bad/no idle, etc). Sometimes the gasket is just loose enough to allow coolant into the engine under a load (much like a tiny crack in a head or block would do). This tiny gap may stay that way for a pretty good amount of time until it finally manages to spread large enough to be very apparent (a larger leak). This is usually caused by an overheated condition that allows the metal near the site of the leak (which is already a hair loose) to bend (warp).
When the leak is this small and only under a load it will likely do nothing more than create a lean condition in the affected cylinder (which the ECU will try to correct by increasing the fuel in ALL cyliders to compensate -the ECU doesn't know that only one cylider is getting too lean). So basically it is not the easiest condition to diagnose when in an early stage like this -therefore any mechanic could easily miss it.
Obviously this problem may not be a head gasket or a crack in the head or block, but the signs are pointing that way. Really, I hate to see anyone have a blown head gasket and don't want to get on here and try to scare people with it, but "if the shoe looks the right size then it just might fit".
BTW if it was the water pump, the engine would overheat at idle or stuck in traffic.
Again, I didn't write this to be an a$$ toward you, mberndt. I just wanted it understood why I thought as I did

mberndt

First, no offense taken, I don't see your response as confrontational...

I already do understand that head gaskets do not "blow" out all at once, and yes, it is not as common to see head gasket failures with metallic head gaskets, as opposed to graphite ones, primarily because of the TENSION strength of the steel is much greater than graphite, making it harder to "blow" out... (materials science) Not to mention the steel has fatigue and ductile properties, and graphite does not...

Considering I've seen both the "blow" out type of head gasket failure, and the slight- leak type of failure, I can honestly say, that if there is ANY, I mean ANY coolant entering the combustion chamber, there will most likely be copious amounts of smoke... This is why I say it would be hard, if not impossible to mis-daignose a blown head gasket... Either failure introduces coolant to the combustion chamber, and coolant only burns white... 1+1=2

I understand you are arguing that a miniscule leak will not necessarily look like a "blown head gasket"... But to a trained eye, in this case a certified mechanic, it should be obvious... Besides, there are other tests to determine if there is a head gasket leak, aka leak down test... That is what I'm saying...

And, your comment about the water pump? My old car DID overheat at idle and while stuck in traffic, the only time the temp would come back down was after a quick revving or downshift... That's why I said it could be the water pump...

P.S. I know your not acting like an a$$, it's just an argument... No hard feelings...

Stackk91

Hi there,
I also have a 91 Prelude, a S modle. And it was over heating all the time, the gauge would just about redline when ever I was on the highway. But if I turned on the defrost/heater on high it would help bring the temp down.
So I told the guy at Lordco and he said to change out my thermostat. I just did that today but I noticed the one he gave me is shorter then the one that came out of my car (yet the same diameter) so I put the new one in, refilled the coolant with the old stuff. (it wasn't completely transparent, defiantly a vibrant green does that mean its done?)

Any ways I took it out for a test run and I barley made it 5 blocks before it was redlining. So the problem is worse, guess I should put the old thermostat in?

I came on here to see if I could find the answer but the problem is this is my first car and I'm just trying to learn stuff as I go so I really don't know to well what I doing.

I saw the stuff about the fans, and my car only has one as far as I can see. (I don't have AC I don't think..) But when I got home I left it running and popped the hood and the fan was stationary.

Stackk91

I didnt bleed the engine properly after replacing the thermostat. redid it and still have problems. However its officially a gauge problem i think.

Fan: now works. or did while i was bleeding it this time. going to check again tomorrow.

When I was bleeding the engine registered a redline. but the fact that i was playing with the release valve proves it wasn't actually that hot. (would also explain why i didn't see any coolant flow or other cooling systems come on.)

Unhooked the temp sensor, (temp zeroed) grounded the wire that connect to the temp sensor and the engine redlined. So gauge and wires work. Faulty Temp sensor me thinks (odd I had just replaced that in Oct. when my car was always registering zero temp in the engine) so i think i just got a dud temp sensor from lordco in Oct.

So gonna get another one of those tomorrow. empty my coolant (for the 3rd time in 3 days) swap em out. refill the coolant, bleed properly. top off the Rad with water. Run it down the street (or till it redlines) pull over and at least see if the fans running. (maybe bring a bottle of water and a wrench to try and bleed the line a bit more?)

that all makes sense right?

Stackk91

turned out to be a faulty temp sending unit.
Didnt think of it as I had just replaced it in October. But I traced the problem there, changed it and its golden.