Temperature regulation assistance

[Melnickta]

The temp gauge on the truck has recently been starting fine, then the heat hand will creep up into the red line. After running there for a bit, it will drop down to a "safe" temp and begin to climb again. I thought this was just a busted thermostat, and I replaced it this afternoon with a new gasket. Drove it just now and the same thing is happening. It's full of coolant, so that's not the issue.

Is it possible to be too full of coolant?

What else could this be?

I'm open to suggestions.

Thanks in advance for the collective wisdom of the board. I'm sure glad there are smarter guys than me out there.
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[Rufton]

Can't have too much coolant.
I would measure engine temp w/ IR gun to be sure engine isn't actually over heating.

[Melnickta]

Would (or could) it be a problem with the temp gauge or sender unit?
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[68gmsee]

Eliminate all the easiest possibilities. You've taken care of the tstat so check the bottom hose to make sure it's not collapsing. Should have either a built in wire coil or wire coil insert. Replace the cap if it's the original and make sure you get the right pressure rating for the engine you have.

As you mentioned it's also possible you have a defective gauge or sending unit. I would go with the sending unit next.

If all of the above don't resolve, you could possibly have a slight leak in head gasket.

[Steeveedee]

Could be an air pocket in the cooling system. If you have a big block, this problem is nonexistent, since the bypass hose allows coolant flow past the thermostat at all times. If you have a small block, it is possible.

What year/engine displacement/etc. is your truck?

As has been mentioned, it is impossible to be too full of coolant...as long as it is mixed correctly for your area.

[Melnickta]

It's a 350 small block. What would be the method of purging the air out of the system if that is the problem? Trying to do all of the cheap fixes first.
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[cdowns]

do you have a fan shroud? is the fan clutch worn out ?

for this type complaint u should take the actual temp of the coolant to see if there is an actual problem

[Rufton]

Originally Posted by Melnickta

It's a 350 small block. What would be the method of purging the air out of the system if that is the problem? Trying to do all of the cheap fixes first.
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I don't suspect air in this case (unless from head gasket as mentioned) because air should burb out when t-stat opened. T-stat opened each time temp went down unless flaky temp indicator.

I agree w/ lower hose check.
I would get a free radiator leak down tester to check for mentioned head gasket, cracked block or head. If you have no other way to check engine temp be sure to keep eye out for coolant boiling out.