Hi All,

I have browsed the threads quite a bit, but Im not quite seeing my symptoms.

When the heat is cranked, at best its lukewarm. It takes forever to warm up the cab or worse yet to defrost the windshield. I have played with the controls, and I can hear the doors open/close, AC kicks and everything there sounds normal, but it never gets warm. I have read all about the core flush, and I know that's possible. I have had on and off SES lights, always for the O2 sensor, but I replaced that and Its been off for a few months. Now its back. And today I noticed that the engine temp is low even after a run on the freeway (see pic), that's as hot as she gets. I read about a coolant thermostat, or possibly that the coolant door is stuck open, so its flowing all the time keeping the engine cooler than normal?

What I am after is the best course of action, I don't wanna to do the flush if its not needed. Would a low coolant temp keep the heat cool? Any thoughts or suggestions are greatly appreciated, Its getting a bit chilly (15F) here in Packer Nation!

Thanks in advance!
Mike

 

Sounds like two problems which could also be interrelated.

It would depend on the car and year and engine type. I only have the service manual for the 1994 S10 Blazer 4x4's. Depending on the engine control module an unheated O2 sensor might trigger a fault when being run below operating temperature.

Now for the cooling system troubleshooting for a 1994 Blazer 4x4 it says:
With cold engine remove radiator cap and put a special temperature marking onto the thermostat housing. (Temp rating 188F or 86.6°C)
Then run the engine and check if you have flow from the engine to the radiator before reaching the 86.6°C which is the temperature at which the thermostat should first open. This is quite generic and should pretty much work on any engine.

Now for a quick check it might be enough to remove the cap at cold engine and start it. If you have flow from the upper hose into the radiator at cold engine already something is definitively wrong with the radiator.

Now if the engine never really warms up it could eventually be possible that it also triggers the O2 fault because the sensor does not get hot enough to provide correct signals. An additional indicator is the heating not going over lukewarm.

Some questions spring up:
Make and model?
Year?
Mileage?
Where is the car from?
Maintenance done by?

 

To me the only thing that could cause cold engine temp is a stuck open thermostat. This is cheap and pretty easy to change-out.
You do need to drain the radiator, then just remove the two bolts of the thermostat housing on the intake manifold to get to the thermostat. Remove it and get a new one.

Low coolant will cause engine to overheat, not run cool.

The SES lite will come on if the coolant temp is too low after driving a set number of miles. Pull the code.

 

You dont need to drain the radiator to replace the thermostat, just take the two bolts out and remove the thermostat housing... clean the old gasket off and replace. very little antifreeze comes out that high anyway.

 

Yep, thermo is stuck open

 

Thanks for the advice folks, much appreciated! What is the thermostat part in need called? I'm not part savvy, and I know there is more than one thermo, thanks! PS, 1998 2dr 4x4 4.6l

 

Thermostat and gasket

 

An old trick to test if it is stuck open is to put some cardboard in front of the the radiator to eliminate air flow through it and then drive it. If you do it, just be sure to watch the temp gauge and once it gets to normal temp stop and remove the card board because it may heat up fast depending on ambient temperature.

 

What you need is a 195 degree thermostat for your truck. Do NOT get a Failsafe unit as they are designed to fail in the open position to avoid cooking the engine. Every one of them I have put in over the years has had to be replaced because it failed.

Either yours is stuck open or someone put a cooler temperature unit in there. On a carbureted engine, this gives a slightly denser charge for more power. On a computer controlled engine, it goes into what is called "open loop" mode. Since you don't have a choke plate, the computer injects more fuel to warm the engine up.

Get the right thermostat in there and not only will you now have heat, your fuel mileage will probably go up. I swapped in a new thermostat in a 1 ton truck once and it went from 6 mpg to 11. You won't see such an extreme increase but it will be noticable.

 

new thermostat will have your heat blasting 5x as hot. Replaced mine due to the same symptoms in like 20mins. You will be happy you fixed it.