Running hot!!

[DieselYJ]

I orginally had problems with the radiator leaking. After i had that fixed i took it for a 45 min drive. It ran good, never got over 200 degrees by the gauge. Stopped and let it sit idleing for awhile, heated up. Shut it off. Noticed that the top radiator hose was not tight enough and had lost a certain amount of coolant. Headed home with it. The temp gauge went up to close to the red and then dropped off to 200 and stayed there the rest of the way home.
Stopped for supper, hour later headed home. Gauge went up to red and did not come back down. So i stopped immediately and filled with water and tightened the hose.
That worked great for another 120 miles. I then started it up and let it sit and idle for 10 minutes to warm it up. But when i took off, the guage went up to the red line and no heat out of the heater. Tried the to check the water level, seemed full. Did not know what to do, so i just drove off. All of a sudden the guage came back down and the heat started coming and everything was good again.
Thought it might be the thermostat or sending unit, so i change both of them. Now the gauge goes back and forth between 240 and red line, but the heat blows good constantly.

Any ideas on what if anything is wrong??

Thanks in advance.

[john8662]

Sounds like air in the cooling system for one, and the wrong thermostat for another. The "Stant" type thermostats as I call them don't work in the 6.2 unless you drill a bypass into the stat yourself. I won't ever run anything but a factory GM hi-flow stat or a Robertshaw extreme duty thermostat, that is also the hi-flow version. Then of course make sure the engine is full of coolant as well as the radiator.

[jackrabbit]

From your description, and the fact that it happenned after your radiator was repaired, it sounds to me as if a rag or something was left inside that is blocking the water flow.

I would pull the bottom hose off to see if there is something there.

[DieselYJ]

I think i will try removeing the stat and seeing how it runs then!!

The rag is what i was thinking, but would it not overheat big time with that much restriction??

Both radiator hoses seem hot, but the radiator does not seem that hot!!

[jackrabbit]

I guess I was looking at it that it is over heating big time with your description of bouncing between 240 and red line.

The thing that really got me thinking that it was a restriction (or partially) was your description of no heat while you were driving for a short time. I will look at the routing of the heater core hose tonite on mine, but I thought that even with the thermostat closed there is always a flow through the heater core, back into the radiator, and the only thing that could block that would be a restriction.

Of course as John pointed out low coolant would also cause that, but I assumed that you had it filled to the top.

I guess I'm always skeptical that when I get something "fixed" and that part is involved with another failure, then I suspect that the part wasn't really either "fixed" or put back together correctly.

[TimK]

I agree with John. Having a large amount of air trapped in the cooling system can cause problems with circulation. If that air bubble gets caught at the water pump, then the pump won't pump and therefore no heat circulating through the heater core or the rest of the block. I have drained my cooling system several times such as the 3 times I fixed the old radiator, when I finally purchased the new radiator and when I replaced the engine. I have never had as big of an air lock as you are describing.

TimK