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Old 08-13-2019, 09:01 PM   #1
doa44green
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Default Radiator overflow

My 31 roadster, with a new radiator and cap gasket replaced twice, will spill over the cap especially while climbing a hill. I know that I overfilled it but I thought the overflow would go out the overflow pipe and not vomit out the cap.
The overflow pipe is not plugged. Are these caps vented?
TYhank you in advance for your thought and experiences!!
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Old 08-13-2019, 10:26 PM   #2
Mike Peters
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Default Re: Radiator overflow

Do you continue to lose coolant, or does it seek it's own level? With engine running, open your radiator cap and look down with a good light to check for foaming, which would indicate a leaky head gasket. A bad head gasket could cause overflowing.
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Old 08-13-2019, 10:29 PM   #3
Tom Wesenberg
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Default Re: Radiator overflow

Radiator caps are NOT vented, and should not loose antifreeze anywhere except out the overflow tube.
Someone may have used a gas cap on the radiator.
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Old 08-14-2019, 11:15 AM   #4
Bob C
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Default Re: Radiator overflow

The gas cap is 3/8" larger than the radiator cap on 30-31.


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Old 08-14-2019, 11:27 AM   #5
redmodelt
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Default Re: Radiator overflow

My thoughts would be; you are not setting the spark correctly, running too lean and overfilling the radiator. Unless there is a bad gasket in place, you may be getting the motor too hot and if overfilling the radiator the water is expanding more then can be pushed out the over flow tube, or that tube is plugged. First checks would be the gasket (make sure there is one or replace as needed) and checking to make sure the overflow tube is clear.

Water only needs to be about an inch over the top plate in the radiator and just below the baffle. Any more then that and it just gets pushed out.
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Old 08-14-2019, 11:57 AM   #6
Chuck Sea/Tac
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Default Re: Radiator overflow

On a plus note, with a slightly non sealing cap, you’ll know when there’s a problem. Assuming you don’t have a temp gauge.
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Old 08-16-2019, 09:29 AM   #7
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Default Re: Radiator overflow

Climbing a hill drives heavier load on the combustion chambers on all four cylinders. With this situation as you describe, I am leaning to a leaky head gasket, and possibly a cast crack someplace. Signs the head gasket is leaking that can be visible from the engine are a slight amount of creosote type ooze at the head gasket. You are kind of describing, to me, that the engine is pumping out the coolant. I am sure there are some tests that others can suggest to get the reason there is pressure forcing out liquid.
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Old 08-16-2019, 09:45 AM   #8
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Default Re: Radiator overflow

There is a simple test that can be run on any engine called a "block test kit" to check for a bad head gasket, crack in head, crack in block, etc. I got mine at NAPA.

It sniffs for combustion gases in the coolant at the radiator fill neck.

You go for a drive then come back, while engine is still running, and sniff for exhaust gases. A test fluid changes color if exhaust gases are bubbled up through it. Easy and conclusive test.
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Old 08-16-2019, 09:53 AM   #9
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Default Re: Radiator overflow

I had the same experience. I was also told by most that the problem was a bad head gasket or cracked block.

One solution offered, however, was that the water pump was moving too much water. I remembered that with my old, original pump that I didn't have the problem. One fix was to reduce the size of the water pump vanes. Another was to install a thermostat in the upper radiator hose to slow the flow.

I installed the t-stat. No more puking out the cap. I now can fill the radiator until I can just start to see coolant above the plate. When the car warms up, the level rises in the top tank but never to the overflow outlet. Been that way for over a year now.

It's a cheap fix...if it works for you.
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Old 08-16-2019, 09:56 AM   #10
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Default Re: Radiator overflow

Plus 1 on the coolant test.

Did a great job on a 1995 Windstar which was "burning coolant" but in which there was an obvious exchange between cylinders and jacket. A Ford issue of that era fixed under warranty by gasket replacement.

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Old 08-16-2019, 09:58 AM   #11
katy
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Default Re: Radiator overflow

Quote:
Originally Posted by Bob C View Post
The gas cap is 3/8" larger than the radiator cap on 30-31.


Bob
On my '31 they're both the same size.
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Old 08-16-2019, 10:20 AM   #12
Purdy Swoft
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Default Re: Radiator overflow

The outside diameter of the caps may be the same but the inside diameter of the 30-31 gas cap , where it meets the filler neck is larger . The 28-29 caps are threaded and the inside diameters are the same and will interchange if you don't mind an over flow when accelerating ..
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Old 08-16-2019, 10:34 AM   #13
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Default Re: Radiator overflow

Sure sounds like a head gasket or you are way under torqued. Drive it slow in third gear and lug it. I bet you get bubbles.
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