mid 1980's civic had 170F thermostats?
 

I'm going to start tuning up my spare 1985 CRX engine befor installing it, and while at the auto parts store they told me that OEM thermostat for it was 170F, and that they had never seen that befor, so I checked with the dealer, and their OEM part is 78C, or about 172F, checked with the shop manual, and it agrees compleatly! now this is a CVCC engine, so it's running lean by design, so maybe it wants to run cool? my thought is that they wanted to squeze all that they could out of this car, after all they left out the sway bars, put plastic front fenders on it, a half sized radiator was standard,in '86 and '87 it had aluminum rear brake drums, if running the engine hotter would have given it better mileage, would they have done it?
My options are 170F 180F or 192F thermostat, I'm tempted to keep it stock, and go with 170F.

My 87 civic has the 1.5 D15a CVCC and full sized radiator. I originally had the 180 degree thermostat but went on up to the 195 degree. The 195 degree was listed as high temp for my car at the auto parts store and the 180 was listed as stock. Maybe the difference between yours and mine was the radiator size. I do notice my temp comes up a little when climbing a long hill that I can't quite maintain speed on.

I found out that the 1.5 CVCC engines are bad about eating head gaskets because of a hot spot in the middle of cylinders 2 and 3 (not enough cooling passages due to the lack of room). My initial symptom was slight boilover at shutdown. Then I noticed that it would not pull fluid back into the radiator from the overflow tank after it cooled down. The next day it was running a little hot and eventually overheated. I also had a black oily residue coating the inside of the overflow tank.

When I pulled the head, the gasket was crushed in the middle of those 2 cylinders. It was still sealing well enough to not let water in to the combustion chambers, but it was letting hot combustion gasses in to the coolant (causing it to run hot) and not sealing well enough to develop the small vacuum needed to pull coolant back in from the overflow bottle.

Felpro makes a special replacement head gasket that has a metal reinforced center to resist crushing and prevent this from reoccurring.

I noticed one Civic CVCC in the junkyard that showed signs of the head gasket issue (someone had rigged up an extra large overflow tank) and I bought a spare engine for $50 from a guy who said his engine was acting this same way.

Since our CVCC engines run extra lean, I was wondering how this was factored in to the o2 sensor output voltages over on the experiment thread.

The Problem with these cars is the Tstat is in the lower hose. Its need to lower temp to open sooner. Everytime we put a normal temp stat in it. Customer would come back and say that the car temp gauge was reading high. We do not install 190+ stats in these cars.

John

John, I have a 195f tstat in my 91 d15b1 civic. I am not sure of exactly what you are saying, but..
1.)my overflow tank level never seems to change
2.)when I come to stop with the engine on or when the key is in the 2 position right after i turn the engine off, the cooling fan is on, even in the cold weather now.

the newly installed water pump leaked a few drops here and there over the summer, maybe that is not circulating coolant. That could also account for the constant overflow level, and fan staying on, but is it normal for the fan to stay on at idle, even when its cold out? The temp gauge stays well below 1/2 at all times.
I should probably just pop in the stock 172f, and slap on a new water pump. :p

I was just assured that the rad fan should come on at operating temp at idle even in the winter, and I double checked my overflow tank when cold, and at operating temp, and it is being used...so sorry for the long post, and for highjacking the thread. non-problem solved! :p

I do have the half sized radiator (14"x15") and it's about 3 years old, so I'll stick with the stock 172F thermostat if the engine has a hot spot, no need to ruin a good block, I'm already ordering a new muffler for the VX from Majestic right now, so I'll drop that on the order as well and have the exact right part at nearly the same price as the parts store.

I didn't describe it well enough in my original post, but the hot spot is in the cylinder head between cylinders 2 and 3. The extra CVCC passages in the head reduced the amount of room engineers had for cooling passages.

There was no block damage from my head gasket episode (and I was happy to see very little ring ridge in the cylinders). I just needed to have the head milled to be perfectly straight before putting it back together.