Just install a new radiator in my 1981 F250. Motor is a 300-6 cylinder. Problem is the temp gauge doesn't go to the normal range like it should. I can run it at fast idle for up to a half hour and it only shows just above cold.
Installed new hoses, thermostat, thermostat housing. Thought maybe the new tstat was bad, so reinstalled old one as it worked fine. Still no change. Heater hoses get warm, upper hose gets hot, but lower hose stays cool.
Any ideas what the issue could be?


thanks

 

Factory gauge ? Get an accurate temp reading , go from there . All may be proper except for your temp reading .

 

Yes it is the factory gauge. Why would that change the gauge reading? Also, I stated the heater hoses get warm, but the cab takes a lot longer to warm up and defrost.

 

Did you "burp" the air from the system? Might have an air pocket.

 

I have read about possible air in the system, but have not read how to do it.

 

New radiator = better heat transfer . You are cooling the engine better . Lack of heat in the cab ? Plugged heater core , improper heater controls . Are you running the proper Thermostat ? What is the ambient temp. in your area ? Many aspects to consider ...

 

Air pocket ... Good advice !

 

I thought about the new radiator transferring heat better. The heater worked fine before, nothing changed with heater controls, 195 degree t stat, same temp as it was before. Air temp around 50 degrees.

 

T-stat in backwards??

 

No, first thing I checked.

 

Check your pump for proper flow . Might not be enough ....

 

What thermostat? My factory gauge is right on C when the aftermarket gauge hits 160 degrees. Really should be running a 195 and that will put it on R or M of NORMAL if the gauge is working correctly.

 

At 192* F my stock gauge reads right dead in the middle. Just for reference.

 

Yep. Mine runs from R up to M as the 'stat opens and closes. And the aftermarket one runs between about 190 and 195 at the same time.

 

The heater core loop is always bypassing the thermostat in every Ford I know.
You should get heat before the thermostat ever opens.

I've never had problems with an airbound heater core, but then I don't have an I-6 either.

If the heater core hoses only "get warm" and "the upper rad hose gets hot" you have a restriction in the heater core.
Maybe dislodged some sludge when you swapped out the radiator?
Try disconnecting the heater hoses and backflushing with a garden hose.

Borrow or buy a non-contact IR thermometer.
(mine was ~$20 and reads -50 to 1,300*F)
Shoot the water neck, aka thermostat housing.

This should give you a *real number* to compare to the gauge.
More than likely your old radiator was not cooling the engine properly and what you thought was "normal" was -in fact- very hot.
My truck always reads just above the "O" in normal.

Ground the temp sender wire to the block and watch the swing.
Try a new sender.
Check that the ICVR is giving the correct voltage.

What made you change your radiator?