STS_Underdog

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 (even though it was 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 a second time. It didn't make any difference this time though.

Yesterday I decided to pull the thermostat housing off and check it out. When I got it off it was pretty gunked up so I cleaned it up and reinstalled everything, being sure the thermostat was properly re-installed. 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)
-up to about 65 mph the temp gauge only drops to 1/4 (from cold)
-at speeds above 65 mph or if driven around town revving the motor higher than normal the temp gauge will drop until it bottoms out

My guess at this point is that the thermostat housing needs to be replaced because it has some imperfection that is preventing the thermostat from sealing and coolant is getting by at higher RPM's because of the increased pressure from the faster turning water pump. Any other ideas? 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? I'm pretty much out of ideas at this point, any input would be greatly appreciated!

89civicdx

Are these OEM honda Thermostats? New thermostat gasket?


Modified by 89civicdx at 12:36 PM 12/19/2004

STS_Underdog

No not OEM, but they each had a new gasket when installed. Seemed unlikely that one that was less than a year old would go bad and then I would get 2 bad ones in a row. At this point I'm considering anything though.

STS_Underdog

Someone on another forum said they though the spring might not be strong enough on non- OEM thermostats and is getting compressed at higher RPM's and leaking. Sounds plausible to me, what do you guys think? Any other suggestions?

MaddMatt

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">increased pressure from the faster turning water pump.</TD></TR></TABLE>

I thought the point of an undredrive pulley was supposed to turn the accessories slower, not faster...

STS_Underdog

Yeah, I meant faster because the engine was turning faster, not because of the pulley making it rotate faster.

solo-x

matt,

on a honda the waterpump is driven by the timing belt. well, unless somebody's swapped in a sr20, y0! FnF!!!

as for the problem at hand i'd want to first verify that the gauge is working correctly and that coolant is definitely moving everywhere it should. even if the thermostat is stuck open there is enough obstruction in the housing to keep the engine temp up when being driven, so my first guess would be something other then the thermostat. i assume the pump is a new honda peice? are both upper and lower rad hoses hot? did you bleed the air out of the system?

nate

solo-x

on second reading, definitely verify that the sensors are wired correctly and fuctioning properly. particularly the water temp sender.

oh, and i have yet to find a non-OEM part for a honda that works better then what honda came up with. (shocks, tires, brake pads, etc. excluded) i worked for a while selling car parts wholesale. i could get just about anything i wanted for pennies compared to dealer prices. after the 4th ignition cap and rotor that went bad in less then 5k miles, 3 sets of windsheild wipers that skipped across the glass, and a dozen or so warped rotors i gave up and started using genuine honda bits. the genuine stuff will cost more up front but typically save you a lot of time and headache down the road. of course, imho, ymmv, yada yada...

nate

STS_Underdog

Nate-

I thnk the gauge is working correctly because the heat I get from the HVAC seems to correspond to what the gauge says (when the gauge drops the heat from the vents becomes cold).

Water pump was replaced, upper rad hose is hot and lower is warm to the touch even before the engine is at full operating temp. I did bleed all the air out after I drained the system each time.

The coolant temp sensor that runs the gauge is under the distributor and is a single wire hookup. I know it's working because it does show the engine temp climbing while the car is idling.

Any other suggestions? So far I think I'm still looking at replacing the thermostat with an OEM and seeing if that helps. If not I'll probably try replacing the thermostat housing with a new one in case it's not sealing properly with the gasket. After that I'm at a loss unless someone has more suggestions. Keep 'em coming!

Mohudsolo

I compared a factory t-stat to an autoparts one and found them to be very different for my GSR. The vent, the way the gasket fit, and the design of the spring housing along with the valve portion all looked different. I would definitely try the factory replacement before looking for any other reason.

MaddMatt

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">on a honda the waterpump is driven by the timing belt. well, unless somebody's swapped in a sr20, y0! FnF!!!</TD></TR></TABLE>

Ah, that changes things a bit.

Matt&lt;---owner of 2 SR20s. yO.

jsi

Try to do a boiling water test with a thermometer and note the temperature the stat fully opens and closes. Try to vary the temperature several times to see if the stat is consistent.

That said, from experience, non-oem "jobber" stats are allways nothing but a PITA, especially on Hondas. I wouldnt even waste the time testing the thing and just get the OEM and see if that solves the problem.

solo-x

interesting...

how cold is it where you are? does blocking off a portion of the radiator help the temperature stabilize?

nate

Todd00

Although I cringe saying this, post the question up in the CRX/EF forum. They may be able to help you out for a problem of this nature.

STS_Underdog

Nate-
I thought that blocking part of the rad off might help, but it feels like a band-aid fix. I've had the car since '98 and I haven't had this problem in previous winters so something is different. I'm gonna pick up an OEM thermostat at work today and get it in tomorrow, hopefully that will solve the problem.

Todd00-

I thought about posting in the model- specific forum but the signal to noise ratio is so bad...

STS_Underdog

Thread back from the dead with an update:

I replaced the off brand thermostat with a Honda part and the problem got a little better but still is not fixed. The temp gauge now reads around 1/4 from full cool unless the car idles for an extended period of time, then it climbs to the normal position of just below 1/2. As soon as I start driving it drops to 1/4 again.

I replaced the thermostat housing in case it had a flaw and wasn't sealing properly but I still have the same problem. I'm looking for other ideas of why my car runs too cool, HELP! I'm also posting in the EF forum, but any help would be greatly appreciated.


Modified by STS_Underdog at 7:00 AM 3/14/2005