New thermostat but still running cold

[Firstgen11]

I've put 3 thermostats in my 90 w250 12 valve cummins and replaced with new gaskets every time and my truck is still only running on cold unless I idle for a while then I get a little heat and it goes to the first line I barely have any heat when going down the road is the reason I know my Guage isn't wrong ive had my radiator cleaned out and new water pump before all this I had great heat but my truck is acting like the thermostat is sticking open but when I turn my truck off my upper hose is just barely warm and it has a lot of pressure I've also checked to make sure it's not air and it's not I'm stumped any help or ideas?

[RCCUMMINS89]

Every non i/c truck that I've been around never gets to the first line. You sure it wasn't running hot(er) before you cleaned the radiator and did the water pump?

[Firstgen11]

Yeah my truck used to run In the middle and after I did head work I got it shaved and stuff and a thicker head gasket and got another water pump and radiatior cleaned and I was loving how it ran cold in the summer but now winter is here and it sucks not having heat

[RCCUMMINS89]

So your heater isn't even blowing cold? If I may, why did you go with a thicker head gasket?

[PToombs]

What did you put in for a thermostat? Cummins or aftermarket?

[ellis93]

Advance your pimp timing,that'll put more heat in the cooling system.

[RCCUMMINS89]

Good advise sir...

[Firstgen11]

I dont want to force it to be warm I just want my thermostat to do its job I've tried cummins and aftermarket thermos and no change I can plug my truck up and there be a little heat and if I let it sit about 20 more mins I have good hear but as soon as I start driving it goes to Luke warm heat it's just over my head it's like the thermostat is stuck open at all times idk if my water pressure is forcing it open or what the problem is it is a 180deg what cummins recommends

[RCCUMMINS89]

Have you by chance checked your overflow tank? Is it full, like to the very top?

[Firstgen11]

Yeah I've kept a check on it And it's not been filling up

[ellis93]

Water pressure will not force the thermo open. The thermostat drops down toward the coolant flow when it opens. When you had the head surfaced,how much was taken off versus how thick of gasket. Did it let you keep the same compression,is the distance between when the piston starts igniting fuel and the head stay the same? That's all things that could possibly screw with the engine creates and manages heat and makes power.

[RCCUMMINS89]

We have a flat deck head.... doesn't matter how much is taken off.... a thicker head gasket ALWAYS lowers compression.

[Firstgen11]

I had it decked 20 thousands and got a 10thousands thicker over stock head gasket they went thru the ports and stuff too and I have mighty diesel head bolts

[Firstgen11]

Don't make a difference but have bigger valve springs than stock too mighty diesel head bolts are stronger than stock they don't stretch they are like studs but I'm bolt form

[ellis93]

We have a flat deck head.... doesn't matter how much is taken off.... a thicker head gasket ALWAYS lowers compression.

True.
That means the compression is off and so is the timing. Bump it up,you'll be making it right not forcing the engine to do anything it doesn't need to.