[Steve91T]

So I've been putting some miles on this engine after it sat for years and I've got a problem that I would like some help with. It's got a new water pump and thermostat, for now the heater hoses are capped off. I'm running a manual fan switch. The water temp gauge is in the drivers should side head.

So everything seems normal except for some reason if I drive down the highway my water temp will drop to about 150 degrees. It acts like the thermostats is stuck open. Yesterday I pulled the t-stat and put it in a pot of water and watched it. It started opening at 180 degrees like it should, then closed when it cooled down.

So why is this happening?

[Steve91T]

So I hooked up the heater core, I now have heat. When topping off the system, I started the engine with the radiator cap off. Doesnt the small stream of water shooting out at the top of the filler neck come from the T stat being open? If so, mine does it when cold. Just took it for a drive and the problem is still there. Somehow water is always bypassing the T stat. Weird problem to have.

[Blainefab]

So I hooked up the heater core, I now have heat. When topping off the system, I started the engine with the radiator cap off. Doesnt the small stream of water shooting out at the top of the filler neck come from the T stat being open? If so, mine does it when cold. Just took it for a drive and the problem is still there. Somehow water is always bypassing the T stat. Weird problem to have.

The small tube in the cap housing goes to the recirc tank, the next small tube down goes to the steam vents at the back of the heads - generally if they are flowing a solid stream of coolant then the air is purged from the system. But.. your symptom of low coolant temperature reading may be consistent with air in the system - the sensor can only measure water temp - hot air or steam isn't seen by the sensor.

When I fill an LT1 I jack the RF corner up so the filler neck is the highest part of the system, fill the radiator, fill the recirc tank to the cold line, then run the motor at idle with the cap off till the expansion from heat starts to push coolant out of the filler, then put the cap on and then crack the 2 bleed screws till a solid stream of water comes out - first put a rag under them to keep coolant off the opti. Warm it up good, let it cool overnight then recheck the recirc tank level - the system will pull some coolant out of the tank as it cools.

CA prop 65 warning - some things I say or do may cause cancer or other bodily harm, reader beware.

This post has been edited by Blainefab: Jan 14 2016, 05:15 AM