I replaced the water pump, thermostat & hoses on my truck (1965 240 six). It wasn't overheating, but the hoses never built up any pressure at all and that didn't seem right. The radiator got hot, but I couldn't see any movement of fluid with the cap off.

So....with everything replaced, I filled the radiator to the top and started the truck with the cap off and let it run for about 30 minutes to purge the system and add the rest of the fluid. But, the fluid level never went down at all. I watched it the whole time and the fluid never moved. So I thought the thermostat must be stuck closed, but when I took it off, it was wide open.

I drained almost six gallons from the truck when I replaced everything, and I've only added about three back in. So I'm back to square one. What gives.... the truck never overheats, but it seems like it won't circulate the coolant. Is that possible or am I in the twilight zone?

 

I hate to start with the absolute basics, but...
Are your belts tight? Do you have a mechanical gauge to measure engine temp?
The fact that you drained 6 gal is odd. Your capacity is only 3 or 4 gal.

When I replaced the coolant/thermostat in mine, the coolant never gurgled down.
I thought it was weird, but it runs at 190* and the coolant has stayed full.

I would say just monitor it. Make sure the pump is turning, coolant is full,
and it's not running hot (monitored w/ a mechanical gauge .
Side note: how's your oil look? Any signs of water in it?

 

Thanks for the reply. I think the basics are what I need here but I'm still stumped.

The belts are tight. The actual amount of coolant I drained out was slightly over five gallons. I know because I filled up old gallon milk jugs.

I'll have to look around for a mechanical thermometer, I probably have one somewhere. I really don't think the motor is running hot though.

Out of curiosity, does your upper hose ever get any pressure on it? I've had my truck for over 10 years, and have driven many times in city traffic at 100+ degrees and have never overheated, but the upper hose has never had any pressure. It seems like the system is not purging. It's like the pump needs priming or something.

 

Sorry to say, without problems I have never payed attention
to the pressure in the upper hose.
Doing random things, I have noticed that the upper hose
can get very hot, but doesn't accumulate too much pressure.

I'll start paying more attention. If posting the day to day
behavior of my motor can help you, I'd be happy to help.

Good luck, Murph.

 

Are you parked on any sort of incline? This can make it difficult for the system to purge air. The radiator cap is the highest point of the cooling system and the air should naturally go that direction.

 

Well, It sounds like from what you say maybe I don't have a problem after all. The heater seems to be working, so some coolant must be circulating even though I can't tell from watching the level in the radiator.

 

fmc - it's on a fairly level spot with no noticeable incline. Would it help to incline the front end a bit, and does it sound to you like there is something wrong or does it sound normal?

 

If the thermostat has a bleeder in it, you won't have any air to purge, it's automatic.