Hows it going guys!? Just got this 91 wagon in a trade. Its has the rt4wd tranny and a zc dohc swap. Everything stock accept for an aem intake. it runs pretty good accept for a few minor issues. The main issue its having is with the engine temp.

While parked and idling the engine gets to operating temp just fine but as soon as i start driving the temp gauge will drop down to below cold and will stay that way until Im parked and idling again. Would this be a bad thermostat possibly?
**(just as a side note, the heater still works great while parked and while driving, and the weather hear in NM has been in the 30's-40's)

Did a search but couldn't find exactly what i was looking for. Just looking for a little insight before I start replacing parts. Thanks in advance for any advice!

Heres a pic in case anyone wants to see

 

Yikes! That is strange!
Nothing like a thorough tune up,when you get a used car.
The thermostat sounds like a great place to start.
Be sure to get one from Honda. This is one of the parts that the version from the auto part stores simply does not compare.

 

Strange indeed! We can definitely agree on that, a tune up and thorough cleaning haha were talking literal cobwebs in the engine bay!
i suppose it wouldn't hurt to replace the thermostat anyways.
thanks for the reply 4dref!
Any other ideas anyone??

 

Aha!
Think I might have just found my answer.
"stuck thermostat, stuck OPEN.

It is allowing coolant to flow through the radiator at ALL times. Therefore when stopped, you have no airflow thru the radiator. This allows car to reach normal operating temps. Once back moving the airflow will cool the coolant/radiator enough to OVERCOOL the car because the OPEN thermostat is not working.

Basically, a thermostat will regulate the amount of coolant aloowed to flow into the radiator to dissapate heat."

Courtesy of this thread:
https://honda-tech.com/honda-civic-del-sol-1992-2000-1/signs-stuck-thermostat-350471/

 

My guess is that you don't even have a thermostat courtesy of the previous owner.

 

Now that would be ridiculous ha. I suppose we'll find out! This would be the correct thermostat for the zc dohc right?
19300-pm3-003

 

I had this same issue. The thermostat was installed and it wasn't stuck open. At least when I pulled it out it was closed. I replaced anyway since I had already bought the new one and the problem went away. Now it stays at operating temperature all the time.

I made sure I bought the one that was oem temperature.

 

Hmm... that's odd that it fixed the problem even though it wasn't stuck open?... well hopefully I have the same luck and it fixes the problem.
I can't really find any temperature specs for the oem thermostat. But all the parts lists I've read for the zc dohc, says to just get one for the 88-91 civic/crx which is the 19300-pm3-003. I believe I read somewhere that the temp rating for this one is around 172°f. Does that sound right or wrong to anyone? Thanks.

 

I didn't think it was going to fix the issue either. My guess is it was just worn out. Maybe the spring wasn't holding as it should when it was cold and let the coolant pass through.

 

I don't know if that temp is correct.

Did you ever figure this out? Did the thermostat fix that issue?