It's Always Something!

[rgshafto]

Had the nose of my '36 Pontiac flathead six coupe this spring to do a variety of maintenance tasks, which meant draining the radiator. Got it all back together the other day and hadn't driven 2 miles when the temp went to 220. It would briefly drop back to 180, then shoot up again. Ah says I, stuck thermostat from sitting all winter. [When I put it up last December it was running fine.]

Replaced the thermostat with a new one, but the same problem continues. Heats up, will briefly cool down again, but then goes right back up. No heat from the heater, so no circulation going on in that circuit. Tested the thermostat I took out and its works perfectly.

The 20-yr old radiator has always been maintained well (flushed periodically, coolant changed every 3 yrs or so) and drains easily. The water pump has less than 1,500 miles on it.

I suspect cavitation in the pump, but don't know how to test for it or how it might be remedied. Any ideas?:confused:

[Bhigdog]

Something put together bass ackwards or possibly a soft radiator hose collapsing.....Bob

[DavidAU]

Could it be the bottom radiator hose sucking flat and stopping the water flow?

Most cars have a wire coil spring inside the hose to stop this happening but it may be missing or deteriorated.

Great minds think alike Bob but I'm a slow typer

Edited April 7, 2012 by DavidAU
posting at the same time (see edit history)

[Luv2Wrench]

I have a 1994 Dodge Ram 1500 pickup truck that does the same thing. I've had the thermostat and water pump each replaced. The behavior for mine is a little different in that most of the time the water temp is 180 and the heat works. However, if I drive slowly or maybe idle at a stop light, the water temp will start climbing quickly. I can race the engine some and eventually (right before I expect it to blow up) the water temp will very quickly return to 180 and, of course, the air from the heater will come out nice a hot.

One interesting aspect is that after 20 or so miles everything works fine and even at idle the temp will not increase.

I will check the hoses as suggested but I'm pretty sure that isn't the issue as those have been replaced before.

[rgshafto]

Hoses are new and aren't collapsing. Some heat in each of them, but not much.

[Joseph P. Indusi]

Both upper and lower radiator hoses should be so hot you could not hold onto them barehanded with a fully warmed up engine. If heater valve is in max heat position these hoses should also be hot to touch. Could possibly be air bound, that is, there is a pocket of air trapped somewhere in the block, usually.

I would drain coolant, loosen the heater hose that is at the highest point in the system and pull it off but keep it ready to put back in place. Now begin to refill the radiator. No coolant should be coming out of the pipe nipple where you disconnected the heater hose; however, eventually you should start to see some coolant begin to spill out. When you have a good flow coming out, quickly replace the hose and tighten the clamp. This procedure for refilling should push any air out ahead of the coolant. It won't cost you much and it is worth a try.

Joe, BCA 33493

[Guest Bob Call]

If you follow Joe's suggested procedure be sure to have the fire department hazmat team on standby to clean up any spillage. Else you may have a visit from the EPA.

[rgshafto]

Thanks Joe, I'll give that a try, with kitty litter at the ready. I've had that nose off a dozen times or more since I bought the car - my 1st in 1965 - and have never had such a problem. Always a first time for everything I guess.