rad fluid pressure
Thread Starter
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Fleet Mechanic
Joined: Sep 2009
Posts: 1,572
Likes: 37
From: Northern Virginia.
rad fluid pressure
it seems on some occasions the fluid flows out of the rad overflow tube.
what would cause this to happen. it seems to be happenning a lot lately.
my first thought is a bad head gasket. oil is clean as can be.
dont know how long this has been happenning. i have only had the truck a
few weeks. this has been the farthest i have drove the truck in a while,
besides the drive from NY to VA. it needs to be topped off fairly often.
since i put the over flow tank on it kind of helped keep the fluid better if
that makes sense.
anything i can look for or test ?
Thanks.
what would cause this to happen. it seems to be happenning a lot lately.
my first thought is a bad head gasket. oil is clean as can be.
dont know how long this has been happenning. i have only had the truck a
few weeks. this has been the farthest i have drove the truck in a while,
besides the drive from NY to VA. it needs to be topped off fairly often.
since i put the over flow tank on it kind of helped keep the fluid better if
that makes sense.
anything i can look for or test ?
Thanks.
Senior User
Joined: Feb 2011
Posts: 183
Likes: 0
From: Grand Junction, Colo.
You may have a weak pressure cap or one that is not at the proper pressure setting. the higher the pressure setting on the cap the higher the boiling point of the rad fluid....if the cap is weak or not the proper setting then it will allow the fluid to boil over at a lower temp than it should normally. You can take it to a radiator shop and have them test the cap. It may cost you a couple dollars but in my experience most will do it for free.
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
since i put the over flow tank on it kind of helped keep the fluid better
Only fill the recovery tank to be half-full. Cold coolant will expand when heated and get pushed out into the tank to up the half-empty volume. It'll then be drawn back into the radiator after it has cooled. After a while, it will find its natural level.
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
I dig it.
The OP mentioned that its already got an overflow tank... but not specifically a recirculating or recovery tank. 'just wanted to make sure that its purpose and function is understood correctly.
The OP mentioned that its already got an overflow tank... but not specifically a recirculating or recovery tank. 'just wanted to make sure that its purpose and function is understood correctly.
Postmaster
Joined: Jul 2003
Posts: 2,544
Likes: 2
From: okc
My factory radiator I had in my 76 had a sticker showing to only fill the radiator till the coolant is about 1 inch over the cores inside. If I topped it off it would seep out the overflow hose till it got down to that level. My truck didn't come with an overflow tank by the looks of the factories routing of the overflow hose. After I bought a new radiator I had to fill it the same way, even my 78 is like that. If you can't bear the thought of leaving it look low then a overflow tank is needed.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Is the truck overheating at all? This happens when the cooling system pressure exceeds that of the radiator cap. It's normal for it to happen every once in a while, but with a good 16-psi cap and an engine running at 195 F, it shouldn't happen all too often.
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Thread Starter
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Fleet Mechanic
Joined: Sep 2009
Posts: 1,572
Likes: 37
From: Northern Virginia.
lots of good info here guys thanks for your help.
i have a 180 stat. yes i probably over filled it a little. i topped it off
right up to the cap. at one point i let it go for a week then it took almost a gallon
to fill it back up. it never runs hot only when it gets low. even then it stays cool
till i get to a stop light and sit before the gauge starts to move. If fluid level is normal,
the gauge does not move no matter what. im sure i need a new rad cap. this one looks
like the original. i did put in a 80's or 90's rad overflow tank. oil looks good. hate to know
if it is going out the exhaust. dont know what to do.
i have a 180 stat. yes i probably over filled it a little. i topped it off
right up to the cap. at one point i let it go for a week then it took almost a gallon
to fill it back up. it never runs hot only when it gets low. even then it stays cool
till i get to a stop light and sit before the gauge starts to move. If fluid level is normal,
the gauge does not move no matter what. im sure i need a new rad cap. this one looks
like the original. i did put in a 80's or 90's rad overflow tank. oil looks good. hate to know
if it is going out the exhaust. dont know what to do.
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Senior User
Joined: Dec 2004
Posts: 438
Likes: 0
From: Palm Bay,Florida
fmc 400 said that rad takes a 16 lbs. rad cap? I got one today(thats what computer called for at autozone) and it was a 13lbs cap? should I run a 16 lbs or do you think the 13lbs one will do?
Senior User
Joined: Apr 2012
Posts: 324
Likes: 0
From: Spencer Mountain, NC
When you get the new radiator cap make sure it is designed for use on a system with a coolant recovery tank (ie. it will allow flow in both directions). The original caps for these trucks were designed to relieve overpressure ONLY. They were not designed to allow coolant to flow back into the radiator from a coolant recovery tank.
Lead Driver
Joined: Dec 2012
Posts: 7,870
Likes: 47
From: Tennessee
When you get the new radiator cap make sure it is designed for use on a system with a coolant recovery tank (ie. it will allow flow in both directions). The original caps for these trucks were designed to relieve overpressure ONLY. They were not designed to allow coolant to flow back into the radiator from a coolant recovery tank.