OK, will a cold car (before thermostat has opened) have coolant running into the radiator from the heater core? Or should the diverter valve block that off?

 

an AC equipped car won't have much if any water flowing thru the heater core with the diverter valve shut, but it will have full flow if the valve is open regardless of whether the thermostat is open or not.

if the diverter valve is shut and the thermostat is shut, then most of the water being pumped is getting recirculated thru the water pump via that little hole underneath one of the water pump bolts to keep it from cavitating.

a non AC equipped car has full coolant circulation thru the heater core at all times and the heater core acts as the water pump bypass when the engine is cold and the thermostat is closed.

 

So if I do have water circulating (a significant amount) with the diverter valve closed, or supposedly closed, then my diverter valve is most likely bad? My car takes forever to warm up, and I'm trying to narrow down the cause. I've triple checked the stat (boiled it every time), I have an HD water pump, but not a high flow one, and both my fans are working as intended. I have a feeling the diverter valve isn't working. It's the second new one I've put in (the first one melted, but not due to an overheat). I'm wondering if it's not a correct replacement part, kinda like the EGR solenoid on this car. I'm guessing a vacuum pump will be enough to check it?

 

all the replacements are of very low quality. (read "chinese junk ") there are no "correct replacements " being manufactured

 

the engine should still warm up even with coolant flow thru the core. and the return line to the radiator is on the side that the water pump draws from, so it's not going to really get cooled off too much before getting sucked back into the engine, anyways.

what do you consider to be "forever to warm up"? it takes a lot longer to warm up if you let it idle than if you start driving right away..

also, what thermostat are you running? if you put in a 160 degree stat thinking you are going to make record setting horsepower, then that might be the problem.. put a proper 195 in there..

 

It's either a 180 or a 195. I can't remember for sure. Idling it takes close to 20 mins. Driving down the road it will never warm up unless I hit stop and go traffic. Even during the summer. And I've checked the accuracy of my temp gauge. It really acts like its a stuck open thermostat even though it isn't. This was an old state patrol car, and they made a lot of changes. Drilled out stat, fans wired on all the time, etc. Been trying to get it all back to stock, but I just can't figure this one out.