Engine not heating up

[kok328]

2002 S-10 2.2L
Started noticing my temp guage running around 170 degrees as it gets cooler outside. I changed the thermostat and noticed that the connector to the temp sensor was cracked, changed that too.
Had to warranty replace the temp sensor because the firsrt one didn't register on my dashboard guage.
Still didn't get heat above 150 degrees.
Warranty replace the new thermostat and still not getting heat above 150 degrees.
Radiator cap test bad at 15psi, replaced radiator cap and still not getting heat above 150 degrees.
The engine is running cool and the cabin heat is not as hot as it has been for the last 5 yrs.
There are no engine codes stored, anti-freeze leaks and level is correct.

I'm lost as to why all the sudden the truck starts running cold and won't build heat.

[j cAT]

you should be running a 15psi pressure cap. do not use any higher than 15psi. this will damage the radiator side / end tanks.

you should be running at 190 deg f.

what thermostat are you using ? who made it ?

many thermostats are not working correctly. best test out first with a pot of water and a thermometer before install. at 150-180 deg f the stat should still be closed.

make sure you installed correctly the thermostat must be setting into the channel securely / no way for coolant to go around the edges. you may require a perimeter gasket to have this effect.

whenever you replace coolant always reverse flow the heater core to remove all restrictive debris. continue until it flows freely. this is a must if you live in a cold area.

[kok328]

I'm running a 195 Duralast thermostat. I removed the original and have put 2 duralast 195's with new O-ring and still no heat.
I installed a 15psi radiator cap.
Even if the heater core was clogged, I would think at least the engine would heat up.
Could I be looking at an air pocket stuck in the system?
I recall a few cars require a bleeder plug to be removed before refilling the coolant.

[j cAT]

Originally Posted by kok328

I'm running a 195 Duralast thermostat. I removed the original and have put 2 duralast 195's with new O-ring and still no heat.
I installed a 15psi radiator cap.
Even if the heater core was clogged, I would think at least the engine would heat up.
Could I be looking at an air pocket stuck in the system?
I recall a few cars require a bleeder plug to be removed before refilling the coolant.

remove the radiator cap . start engine and run until the engine heats up . rev a few times. this should remove the air if any.

place you hands on the heater hoses both should be hot. if not then there is no flow. if the hoses are both hot then it would be an air box issue.

the top engine hose should be hot at the thermostat mount.

some engines do have bleeder fittings. with the engine running you open slowly to purge air out. an air pocket can cause no flow thru the heater core, as well as a plugged up heater core which I have had occur even on new vehicles.

[aleekat]

Seen several that take over 30mins to burp the system.

[rcweston]

Originally Posted by kok328

I'm running a 195 Duralast thermostat. I removed the original and have put 2 duralast 195's with new O-ring and still no heat.
I installed a 15psi radiator cap.
Even if the heater core was clogged, I would think at least the engine would heat up.
Could I be looking at an air pocket stuck in the system?
I recall a few cars require a bleeder plug to be removed before refilling the coolant.

I've had heat problems in three s10's. The first was a 4.3l and the last 2 are both 2.5l. In all three, the engine just seemed to take forever to warm up, even after an hour of driving. The heater never did get much past a luke warm in the winter. In the summer it was ok.
I changed the thermostats many times but it didn't help. I thought they must have been letting it leak / bypass the thermostat some how and would put paper in front of the radiator. It helped a little but didn't solve the problem. I was baffled and finally gave up.
A freak chance of another problem pointed me to an answer for the heater problem. After years of just living with it, I finally had somewhat of an answer.
The hose to the heater core input ran from the output of the engine, just before the thermostat, then into the intake manifold housing, then into the heater core and back to the radiator to be sent back to the water pump. By going first to the intake manifold, most of the heat was removed from the antifreeze before it got to the heater core. No wonder it never warmed up!
To solve the problem, I added a second hose from the output of the engine directly to the heater core then tee'd the first line and the new line back together before they returned into the radiator. The engine warms up, the cab now warms, and the intake air still gets warmed. Were all three much happier now. How this helped warm the engine is still a mystery to me, but it works!