86 2.9L overheating problem

[Cameron1591]

So I recently replaced the heads, all gaskets, head bolts, put in a 180 degree therm and its wanting to overheat after like 20 minutes of running. Not showing any signs of coolant in oil or coolant leaking anywhere. I can tell the radiator is circulating. It appears the water pump is as well since the inlet and outlet hoses get hot.
Any suggestions on what may be causing the issue?

 

[BlackBII]

Do you have a mechanical fan still? Is the clutch on it engaging?

 

[RonD]

Is the heater blowing hot air?
So no air lock or blockage.

Have you felt the rad with engine hot but off, see if there are any cool spots where coolant is not circulating?

With engine warmed up and running feel the upper and then lower rad hoses, if upper is much harder to squeeze than the lower then rad is blocking flow.

Is rad cap allowing coolant to be pushed into the overflow tank?
And does all the coolant return to rad when engine cools down?
Put a piece of tape, marking the level, on the overflow tank when engine is cold, then run engine up to operating temp and let if cool back down.
See if the level is higher or lower than the taped level.
Higher means overflow tube may have a leak, sucking some air back in when cooling.
Lower means you have a leak or had air in the system prior to test.

Rad caps can go out of spec so won't hold as much pressure, this lowers the boiling point of the coolant and can cause steam to form in the head which leads to rapid overheating cycle.
Overflow tank level would get higher than "normal" and you would see bubbles coming up in the tank.

 

[Cameron1591]

Yes it does have a mechanical fan and it is engaging properly.
The heater blows hot air but not very powerfully. Doesn't defrost in the cold very well.
My overflow coolant level seems to stay relatively the same after cooling back down.
I'll check the other things you suggested and post what I find out.

Thanks for the help guys

 

[BlackBII]

When you say it wants to overheat, what are using for that assertion? The gauge on the dash? An actual temp gauge? Radiator cap steaming?

Sometimes the in dash gauges are inaccurate.

 

[Cameron1591]

I'm basing that off the in dash gauge. I haven't had access to an accurate temp gauge.
I believe the radiator is clogged now. I felt it after heating up and only the top was hot. Over 3/4 of it was still cool. I'm going to the junk yard to get a replacement and hoping that takes care of the problem

 

[RonD]

Also reads like the heater core is getting plugged up.
It is just a small radiator so if the big one has gotten clogged up from debris in the system, you can bet the small did too.

Often you can back flush a heater core to get a few more years out of it, if it's not leaking.
Lots of videos on back flushing a heater core.
Basically you run water thru the core in the opposite direction of the coolant flow, this can push out any larger particles the way they came in.
You can also fill the core with warm water and CLR, let it sit for 20min. then back flush again.

 

[fyre82]

If part of it was hot and the rest was cold you may not be all the way warmed up.
My 2.9s take at least 3 thermostat cycles to completely warm the engine to 195 degrees.
There's another thing that might contribute is you say you put in a 180 degree? IIRC the spec is 193-197.

You can check it in the driveway.
I block the wheels and all the safety stuff to keep it there.
Slip a piece of cardboard over the front of the radiator, not big enough to completely cover it, but mostly.
Run the engine with the rad cap off, if its not completely full right now that's good, less spill chance.
Watch the fluid flow as it warms up, it should start at a trickle, then more and stop when the thermo closes. This should happen 2-3 times with a 195 thermo.
When the coolant reaches the temperature of the thermo opening it should flow steady, check your gauge.
Pull out the cardboard and let the engine cool a bit before you shut it down.
If at any time is starts to boil, you'll know, clear the cardboard and cool off. You can overheat doing this! So pay attention to the temperature as you are there.

This tells you several things:
Thermostat is working.
Water pump is working.
Radiator is flowing air and water.
Where your gauge reads relative to thermostat cycles.
Where your gauge reads at normal temperature.

I do this with cap on to test a repair or for the same reasons as above.

Another one, does your radiator flow air? They clog outside as well.

Sorry for the novella . . .

Good luck
Rich
Good luck