1978 300, small radiator, 3+OD trans.

I have filled the radiator up to the required level, an 1 1/2" from the lip right? But every time I park the truck the rad will puke out some coolant. It would puke for several stops. It finally has stopped puking when I park but I can't see a fluid level when I remove the cap to check the level. I've searched the archives and can not find anything specific to my problem. I don't like having this little coolant in the system since summer is here and it's only getting hotter in Texas. My fan tips are only 1/2" from the radiator, so I would think getting a bigger spacer is out of the question. I've looked for fan shrouds, but none are offered for my tiny radiator. Could my t-stat not be operating properly? Like not opening all the way? I have a 13# rad cap, that is correct, right? I have not seen the TEMP gauge pegged yet. Any suggestions would be great, thanks!

 

Does your truck have an overflow bottle or bag? This would have a rubber line which attaches to the tube coming out of the radiator by the radiator cap. Later model trucks have these and any coolant which is released when the engine actually gets hotter, just after shut down, flows to the recovery bottle. As the engine and radiator cool, the coolant is drawn back into the radiator.

You could find one at a junkyard or get a universal replacement one at most parts stores.

 

Ummm.... I hate to be the harbinger of bad news, but that is EXACTLY what mine was doing BEFORE it blew a head gasket,,,

https://www.ford-trucks.com/forums/1...-300-help.html

 

@1986F150six- I do not have a recovery tank/bottle/bag. I was thinking of putting one in to take care of the problem. It seems to only puke after shut down, not while driving.

@PickupmanX2- I hope you are wrong! My other truck is down for repairs so I need this one running right now!

 

Mine was doing this after a rebuild. I found out I wasn't filling the radiator correctly (sounds stupid but there is definitely a correct way to do it):

(1) Take cap off and fill it
(2) Leave cap off and start the engine. Run it until the thermostat opens up (the upper radiator hose will get hot).
(3) Fluid level will drop in the radiator after the thermostat opens. Fill it up some more.
(4) Keep running it. Thermostat will open/close several times and each time you will probably need to fill it a little more.
(5) Shut it down and put cap back on it.

Don't worry about the cap not being on. It is only dangerous to take the cap off AFTER the system has built pressure. With the cap off, it won't build any pressure. BUT turn the motor OFF before you put the cap back on - pressure can build quickly and it might start spraying before you have the cap all the way on.

With the cap off, it might overflow a little bit as it warms up. This is due to unconfined thermal expansion of the coolant. You will think it's full because of this, but it's not. You'll have to wait for the thermostat to open - the fluid level will drop down and you'll be able to add more coolant then.

I'm pretty sure what happened with mine was after shutting it down, no coolant is flowing, some coolant gets super-heated in the head, turns into steam, and pushes coolant out of the radiator cap. It is able to turn into steam because it isn't filled all the way (i.e. there is "air" in the sytem). With the system properly filled, it maintains pressure when hot (max pressure at the radiator cap) and that helps keep coolant from turning into steam. You also have more heat absorption capacity because there is more coolant.

Hope this helps.

 

Most thermostats have an 'air bleed' hole to allow the coolant to flow into the block and heads. Meaning, basically you can fill the system pretty close to full if you wait for the air to bleed into the upper radiator hose. Once the air is in the upper hose, you can use manual compression to 'burp' the air into the tank, and then allow coolant to flow back, filling the upper hose.
I would use that process, and then heat cycle the engine from cold to hot to cold, and measure the coolant level, reassuring myself that the tank was full cold if it had an expansion tank, or filled to the 'cold fill' line if it did not.
If you fill the radiator upper tank completely, it will expel coolant even if the temperature does not exceed design. The coolant will expand, and it will push past the cap seal. Older designs left air in the tank to be compressed or expelled as the coolant heated. When hot, the coolant should fill the tank completely or close to full.
To prevent that, you need an overflow tank and a radiator cap with a return valve & cap seal. Then you can fill the tank full, and expansion will flow into the expansion tank and be drawn back into the radiator upon cool down. That prevents air from being in the cooling system, and insures the radiator is full.
tom

 

take the truck to a good mechanic and solve the problem
Putting hours of your time on it and pay for parts replaced, maybe not the right
solution
A simple coolant pressure test will do more than anything else

 

I added a coolant overflow tank and replaced the cap. The rad kept on puking. I drove it over to my parents getting ready for a trip and found the top tank sprung a leak right where the tank meets the core. I took it to my radiator shop and he had to replace the core on it. I have it back together, replaced the thermostat while I had it apart. Pre-filled the block as much as I could before installing the thermostat, put it all back together and it hasn't puked since. That has been 2-3 weeks ago. The radiator guy said I had a bad cap. I'm not sure, but it works fine now, not even puking into the overflow tank. Thank you for the help and suggestions. I was going to have it tested, but when I sprung the rad leak it kinda changed things.