Tom454

I asked the question on the C4 tech forum but received no replies. I know there are some C4 members here... so I'll try my luck.

Background:
1987/C4 all factory. One electric coolant fan (no aux coolant fan). ECU reads a coolant temp sender (not a switch) in the intake. Based on temp, turns the fan on via a relay by grounding the relay coil. Fan supposed to only come on at very high temp. (220+) Hence, a high value thermostat is stock. This is all for emissions purposes. The ECU supposedly makes other decisions (rich/lean/timing/evap etc) based on the same coolant sender.

History:
Previous owner removed the relay and had a on/off fan switch mounted in the dash. The driver had to constantly monitor the coolant temp and manually turn the fan on/off as required. In driving the car, I found it necessary to constantly keep turning the fan on & off. I removed all this and rewired it back to stock, installed a new relay etc. He had a 160 thermostat installed. He also had a Hypertech chip laying under the drivers seat... apparently another failed attempt to modify the factory system.

My wife will be driving this car and I can't expect her to monitor the coolant temp.

Question:
I have a 160, 180, and 195 thermostat. Which one should I use?

Edit: This car is not currently subject to emissions testing.

Kubs

There are LOTS of discussions on lower thermostats vs HP. The fact is that without changing any part of the cooling system the water temperature will reach the same equilibrium regardless of the thermostat being used. The lower temp t-stat gives the cooling system a "head start" so to speak. For street driving you need heat to burn off moisture that collects in the crankcase as it warms up. I run a 180° thermostat in my '90 race car and also used a 180° when I drove it on the street. IF the fans are working properly and the radiator is clean you should not have any cooling issues.

7T1vette

You should install the 195*F thermostat. The computer on your C4 runs in "default" mode until the engine reaches operating temps. The factory installed stat was a 195*F unit. You need it for the system to work correctly.

P.S. The only thing the thermostat does is allow the engine to warm faster than it would without a stat. The normal operating temp for a C4 is around 200-210*F....stat or no stat. It only takes longer to reach that temp if you have no stat or a lower temp stat.

terry82

I would check to see what chip you have .go back to all factory settings .As has been said, use the 195.

cv67

If you use the Hypertech it will turn the fans on sooner so use the cooler stat

I dont know why people bypass systems and replace a 10 or 20 dollar switch when the right fix is so easy. Hope you get it where youre happy with it. I used the HT Chip just to have em come on earlier didnt like that hot running business still passsed Ca smog no problem.

gungatim

C4 owner here. Not on the c4 section very often because they are so reliable.

at any rate. I would run the 195. put the proper CTS back in, the fan relay, etc. flush the system and refill with good 50/50 and call it a day.