So I've got an unusual problem with my 1991 STS Civic. I just did a stock rebuild on the motor (only change was to add an Unorthodox Racing pulley) and came across an interesting problem while breaking it in. I was in the mountains and I noticed that any time I would coast for an extended period of time the engine temp would start dropping and would keep going until it bottomed out the gauge. I replaced the thermostat and gasket (even though they were less than a year old) and that seemed to fix the problem. Unfortunately it came back a few weeks later so I replaced the thermostat and gasket a second time. It didn't make any difference this time though.

The first thermostats I used were just generic from the parts store so next I bought an OEM thermostat and gasket from the dealership. This helped the problem but did not solve it. Now the car will warm up to 1/4 of the way up the temperature gauge and will hold there but it won't warm up to the normal operating range (just below 1/2) while the car is being driven. If I let the car idle it will warm up normally (just a little slow) but as soon as I start driving it will drop to around 1/4.

Next step was to replace the thermostat housing because I thought the thermostat might not be sealing against it. Made the change but no help.

To summarize, the symptoms as of now are:

-car will warm up normally if left idling
-heat corresponds with the temp gauge (ie blows warm when the gauge is up, cold when it is down) so the temp gauge seems to be accurate
-when driving the gauge drops to 1/4
- if I stop and let the car idle the gauge will warm up to the correct operating temp until I start driving again

I'm pretty much out of ideas at this point. Is there a gasket somewhere I could have forgotten or put in wrong during the rebuild (my first) that would let coolant bypass the themostat? Other than the temp issue the engine is running great, I just really want to track down this issue. Any advice would be greatly appreciated!

 

that was the most professionally stated question i think ive ever seen on here.

when my thermostat was stuck open it gave your symptoms. replacing it did the trick for me.

i would suspect your temp sending unit is bad. its a sensor on the block that may be sending false information.

they are cheap too, which is good. aside from that i would say its something with that pulley... but if its an underdrive that would only make the engine run hotter, not colder... so actually i dont think that has anything to do with it.

good luck

 

Very good question.

What is the outside temp where you are at?

Maybe try putting some cardboard in front of your radiator? or it could be a faulty thermostat again.

 

I'd say replace the sensor. The thermostat can't go bad that many times.

 

My buddies EG has a hard time warming up, this winter I haven't seen it go past 150 accpet maybe once or twice when we were driving on my paper routes(even then it takes FOREVER to get there) . Did you switch out the radiator? Maybe you could try a higher temp thermostat? Just a thought,

good luck

Blaze

 

Wow, it's pretty rare to see an overcooling problem. In fact I don't think i've seen it ever asked. Sounds like a sensor issue if you've changed the thermostat already a few times. But I'm clueless and I'm more interested in seeing what the outcome of your problem is for future reference.

Good luck!

Bumpity

edit****

Now that I re-read your problem, I don't think the sensor is the problem. I also don't see how you can bypass the thermostat. I think a higher temp thermostat would only be a bandaid to the problem b/c if everything is stock then there is no reason why stock shouldn't work. In fact, stock thermo should be fine pretty much regardless of mods in your case. What affect does the pully have on the water pump? Is it pumping water through too fast? I don't know if that makes sense. Have you tried putting the stock pully back on just to rule it out. That would probably be my next move.


Modified by 88 rex at 10:57 PM 3/13/2005

 

I don't think the sensor is the problem mainly because the HVAC temp seems to correspond with what the gauge tells me. When the gauge shows cold the heat blows cold. As it warms up the heat begins to blow warm. I'm getting to the point where I'll try almost anything though so I may give it a shot.

The underdrive pulley only drives the alternator and a/c on the EF and I pulled the A/C a long time ago. The water pump runs off the timing belt so it shouldn't be affected.

The radiator was replaced 1.5-2 years ago and I haven't had any problems from it since the replacement.

I thought about blocking off part of the radiator but I decided that would only be a bandaid, I'd rather get to the cause of the problem. I've had the car for 6 years and haven't had these problems until now. I really thought it was the thermostat stuck open but I just have a hard time believing I could get that many bad ones in a row. The one in the car when I rebuilt the motor was replaced when I put the radiator in the car. Since the rebuild I have put a total of three more in it trying to solve the problem. The OEM unit that I put in last gave some improvement but didn't solve the problem.

Outside temp doesn't seem to matter, I've had the same issue with the outside temp ranging from 20-70 degrees this winter. I also autocross the car regularly and the temp does the same thing when being driven hard, not just at street speeds.

Any other suggestions? If not I'll probably try the sensor out of desperation but I really think there is something else going on. Keep the ideas coming, thanks!

 

EDIT...I repeated a few things you just said. This is cetainly interesting, I am baffled.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by STS_Underdog &raquo;</TD></TR><TR><TD CLASS="quote">I don't think the sensor is the problem mainly because the HVAC temp seems to correspond with what the gauge tells me. When the gauge shows cold the heat blows cold. As it warms up the heat begins to blow warm. I'm getting to the point where I'll try almost anything though so I may give it a shot.

The underdrive pulley only drives the alternator and a/c on the EF and I pulled the A/C a long time ago. The water pump runs off the timing belt so it shouldn't be affected.

The radiator was replaced 1.5-2 years ago and I haven't had any problems from it since the replacement.

I thought about blocking off part of the radiator but I decided that would only be a bandaid, I'd rather get to the cause of the problem. I've had the car for 6 years and haven't had these problems until now. I really thought it was the thermostat stuck open but I just have a hard time believing I could get that many bad ones in a row. The one in the car when I rebuilt the motor was replaced when I put the radiator in the car. Since the rebuild I have put a total of three more in it trying to solve the problem. The OEM unit that I put in last gave some improvement but didn't solve the problem.

Outside temp doesn't seem to matter, I've had the same issue with the outside temp ranging from 20-70 degrees this winter. I also autocross the car regularly and the temp does the same thing when being driven hard, not just at street speeds.

Any other suggestions? If not I'll probably try the sensor out of desperation but I really think there is something else going on. Keep the ideas coming, thanks!</TD></TR></TABLE>
i just started a post stating the same exact problems you are having to the tee there is not one symthom that you stated that i dont have i posted mine 3/10/05(check my last posts) and no one can help me either i read your post the other day and kept trying to tell myself it could be the sensor but like you said the guage goes up and doun till driven if you EVER FIGURE THIS OUT PLEASE PM ME ASAP!!!!!!!!!!! and GOOD LUCK

 

Hmm, I wonder if a hose is crossed somewhere on the back of the block. Check the ones coming off the water pipe that goes from the t-stat housing to the water pump.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Runnerdown &raquo;</TD></TR><TR><TD CLASS="quote">Hmm, I wonder if a hose is crossed somewhere on the back of the block. Check the ones coming off the water pipe that goes from the t-stat housing to the water pump. </TD></TR></TABLE> i checked all of mine to my friends and there are mint {sorry to jack in post }

 

Damn, I thought you might be on to something but I just compared the lines on my 91 to the ones on my wife's 89 and they are routed the same. Two large hoses, left one to the heater core and the right one to the intake manifold. Also a small one running to the EACV on the back of the intake.

Is there any way it could be a heater core problem? The return for the core comes in just below the coolant temperature sensor under the distributor. I don't see how it could be, how could the coolant get cooled off? When the thermostat is closed the coolant should just be pushed around the head and through the heater core by the water pump, right? Am I missing something?

Keep the ideas coming, I'm still stumped.

 

Is it a stock radiator cap? cause if not that could be causing to run cooler no?

 

Same one I was using before the rebuild without any problem. Good idea though.

Keep 'em coming!

 

perplexing problem - watching with interest.

 

my car runs cold too. but it runs fine when warm outside,(gets up to temp) but if its cold, the motor statys cold. i have a b16 witha full length radiator

 

My brother seems to have the same problem in his 88 crx si. It will warm up just idling but after normal driving or hard bursts it drops down really low sometimes all the way to the bottom. And it also blows cold air if the gauge reads cold and warm if the gauge is.

 

We once had a car towed into the dealer and it had the same problmes, The guy before had the thermostat in backwards...the bi-metalic disc and spring still work but not that well B/C the hot coolant has to heat the metal through the thermostat housing...I'd check that and Ill talk with the guys in the shop.


Modified by GreenBean at 10:27 AM 3/14/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GreenBean &raquo;</TD></TR><TR><TD CLASS="quote">We once had a cra towed into the dealer and it had the same problmes, The guy before had the thermostat in backwards...the bi-metalic disc and spring still work but not that well B/C the hot coolant has to heat the metal through the thermostat housing...I'd check that and Ill talk with the guys in the shop.</TD></TR></TABLE>

interesting

 

It was interesting, especially the way he got it to fit in there

 

since i have a b18b the stat wont go in backwards cuz it wont fit

 

Nope, the spring in on the water pump side where it shoud be. Did anyone at the shop have any ideas? I'm still open to suggestions!

 

ok im looking at my helms as we speak:

couldnt the heater core be stuck partially open, allowing coolant to flow thereby not heating up as fast on the block itself... i strongly suspect this is acting like a thermostat bypass of sorts, which wont give any symptom other then a really long warm up time.

youve also got 2 thermosensors on that block as well as the temp sending unit.

the temp sending unit may be fine, thereby allowing the guage to be accurate, but what about the other two?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by doublethink &raquo;</TD></TR><TR><TD CLASS="quote">ok im looking at my helms as we speak:

couldnt the heater core be stuck partially open, allowing coolant to flow thereby not heating up as fast on the block itself... i strongly suspect this is acting like a thermostat bypass of sorts, which wont give any symptom other then a really long warm up time.

youve also got 2 thermosensors on that block as well as the temp sending unit.

the temp sending unit may be fine, thereby allowing the guage to be accurate, but what about the other two?</TD></TR></TABLE>
that is so right there is 2 on the pass side of the head and on older motors the fan temp switch on the back of the block but on the newer motors it is in the rear thermostat housing w/ the stat but it isn't connected on my motor will do that tomorrow asap and post result(not to mention i put in my rad fan to see if it works when i let the car warm up at idle but it never came on so i checked the manual and i never had it hooked so CROSSING FINGERS will let know out come tomorrow

 

Both good ideas, guess I'll have to pull out the FSM tonight and figure out how to test the thermosensors. If that doesn't work I guess I need to look at the heater core. Would the easiest way be to just bypass it and see what the temp does? Thanks for all the ideas!