correct radiator cap pressure
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Logistics Pro
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From: Deerbrook, WI
correct radiator cap pressure
My truck is a 52' F1 with a 215cid I6 engine. I recently purchased a new radiator cap. The guy selling it said I should go with a 10 pound cap because I have a new modern radiator. I mentioned that I thought a 4 pound cap was what was probably used back in the day for trucks like mine. His response was that a 4 pound cap would just waste antifreeze by allowing the radiator to boil over excessively. Is he right? Thanks.
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Logistics Pro
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From: Deerbrook, WI
Thanks, Ford348. I was pretty sure a 4 pound cap was the one recommended for trucks like ours. Would I be right in thinking that a higher pressure cap could be a factor in a head gasket failure? My head gasket is already suspect because my truck sat without being run for a very extended time. Who knows what the antifreeze was eating away at for all those years? I'm thinking maybe the head gasket?
Hotshot
Joined: Oct 2009
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From: Burbank, WA
As you surmise, the more pressure you put on things, the quicker you'll find weak links. I'm not sure if the 4 pound cap was a limit for the engine, or the radiator. My guess is the radiator as they may not have been built as strong as rads today, and you could utilize a higher pressure cap with a modern rad, but why chance it? The system was designed for 4 pounds. My 2c.
Logistics Pro
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From: Bothell & Silverdale, WA
Back in the day thermal efficiency wasn't much considered, but we all know today that it's much better for everything to run it hotter, oil included. Running increased pressure lets you run increased temperature, like 180° to210° F without vaporizing the coolant. In either case it would be imperative to have a coolant recovery system installed.
The only problem I see with running a 10 lb. cap is the coolant pump seal. If it's the spring loaded carbon/ceramic type, no problem. If it's the old style packing type, keep an eye on it.
The only problem I see with running a 10 lb. cap is the coolant pump seal. If it's the spring loaded carbon/ceramic type, no problem. If it's the old style packing type, keep an eye on it.
Lead Driver
Joined: Aug 2006
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From: Brentwood, TN
Just to establish a bit of perspective...cylinder compression is over 10 times that of the higher pressure cap that you are concerned about. If the cylinder pressure does not leak, then how much concern is warranted for the coolant pressure? That said, if the condition of the head gasket is that poor then it's time for a change.
Fleet Owner
Joined: Jul 2004
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From: NM
The radiator is the limit on pressure for the cooling system. Above 4 psi your upper tank may bow or split at the seam.
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Pic: Scroll down to 8100 CAP - RADIATOR.
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Post Fiend
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From: Waterloo, Iowa
He has a new radiator though? I've heard in this instance the concern would shift to the heater core. Don't know how true that is.
Lead Driver
Joined: Aug 2006
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From: Brentwood, TN
Any radiator built in this decade should handle 10 psi no problem...as should the original OEM. Food for thought...at 75 degrees, a can of Coke has an internal pressure of 75 psi. If a Coke can handle 75 psi then a radiator should handle 10 psi without breaking a sweat.
Logistics Pro
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From: Bothell & Silverdale, WA
When I used to get radiators recored and repaired they were always tested to 20 psig. That was in the '70's. The only things I would be concerned about is the condition of the hoses and the coolant pump seal. I have seen old engines overheat to the point of blowing off steam through the radiator cap, and never bulged out the radiator tanks.
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Logistics Pro
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From: Deerbrook, WI
Thanks guys.
My radiator is new and was purchased from classic haulers. It is an OEM style cooper and brass radiator. My water pump is new also, but I am not sure about the type of seal it has. It had better be the best as it was very expensive.
My thermostate does seem to be working. There was no flow when I started the engine. After 20 miles, there was movement, but the engine still wasn't very hot. The temp gauge stays on C, so I'm not sure if the gauge is working. It does go to H, however, with the ignition turned off.
I was just concerned that my head gasket might be failing because there was so much sludge in my antifreeze and on the radiator cap. With the cooling system flushed and new antifreeze, everything looks good at least now.
My radiator is new and was purchased from classic haulers. It is an OEM style cooper and brass radiator. My water pump is new also, but I am not sure about the type of seal it has. It had better be the best as it was very expensive.
My thermostate does seem to be working. There was no flow when I started the engine. After 20 miles, there was movement, but the engine still wasn't very hot. The temp gauge stays on C, so I'm not sure if the gauge is working. It does go to H, however, with the ignition turned off.
I was just concerned that my head gasket might be failing because there was so much sludge in my antifreeze and on the radiator cap. With the cooling system flushed and new antifreeze, everything looks good at least now.
Logistics Pro
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From: Bothell & Silverdale, WA
Glad to hear that. I would still go for the coolant recovery jug though just to keep all the air out of the system. Your radiator stays completely full because there is a vacuum release built into the radiator cap that will allow coolant to be drawn back in when it cools, and not air.
Logistics Pro
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From: Bothell & Silverdale, WA
I have one of these that I bought at NAPA many years ago. They are very reliable. The fluid is cheap too. Mine has a bulb on the end like a turkey baster.
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