Coolant system testing

1945 - 196*, Willys CJ series, questions, discussions, regarding anything related to the post war jeep.®
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douglasmthom
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Coolant system testing

Post by douglasmthom » Tue Sep 18, 2018 2:54 pm

I tried renting/borrowing a coolant system pressure tester from all the local automotive stores, but their adapters are all too small for the GPW radiator cap. Is there particular kit anyone knows of that fits this radiator? I realize I could make up something that would tap into a threaded drain port, but I was hoping to avoid that.
Doug Thom

Chassis GPW 84536 - DOD: December 9, 1942 Dallas, TX
Engine GPW 89702 - early January 1943
Hood Number (est.) 20192259
MVPA 34210, MVCC 12569

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Re: Coolant system testing

Post by artificer » Tue Sep 18, 2018 11:10 pm

Just get an old non pressure cap that fits the fuel tank drains on a G503.
Drill a central hole in this cap large enough to pull in & seal a tubeless valve stem.
Make sure the brass seal that seats on the radiator neck top is still intact & held in with the valve stem seal as well.
Fit the modified cap & with a bicycle pump, pump up to about 6 psi.
Feel what the radiator hoses feel like, then come back in 10 minutes & recheck to see if the same tension on hoses or there is a puddle on the ground.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

Wolfman
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Re: Coolant system testing

Post by Wolfman » Wed Sep 19, 2018 5:49 am

:idea:
What a novel idea !
I might make one of those for myself.
I will add, plug the over flow tube. You will have to pump a long time to get 6 lbs. if you don't.
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douglasmthom
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Re: Coolant system testing

Post by douglasmthom » Wed Sep 19, 2018 7:16 am

Thanks John,
I believe I have a spare cap for the tank well.

While preparing to do pressure testing I found the source of my coolant leak. My radiator cap(s) are not sealing properly and when the thermostat reaches temp and opens I'm dumping a quart of coolant out the over flow tube. I have two caps - one from Ron with a rubber seal attached to the cap and a Ford Repro from AJP that comes with a fiber gasket. Both exhibit this problem. Even when I use the fiber gasket with Ron's cap it slows the leak, but its still there. The radiator opening is in good shape, clean, flat, not mis-shapen in any way and its an original GPW radiator.

After making some measurements, it would seem like my filler neck is deep enough to keep the springs on the caps for depressing and making a good seal. I suppose I could get more fiber gaskets, or make my own thicker gasket....

Anyone run into this problem before? I discovered it by letting the jeep warm up in the driveway with a bucket under the overflow. Normally I'd be on the road dumping my quart out on the City streets where I'd never see it.
Doug Thom

Chassis GPW 84536 - DOD: December 9, 1942 Dallas, TX
Engine GPW 89702 - early January 1943
Hood Number (est.) 20192259
MVPA 34210, MVCC 12569

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douglasmthom
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Re: Coolant system testing

Post by douglasmthom » Wed Sep 19, 2018 11:38 am

Okay - I seem to have a fix on this problem. The fiber washer that came from AJP cap was .080" thick. So I went to the local auto part store a found a 0.125 thick rubber washer with the correct OD and I cut the ID to match the original fiber washer. When installed with the AJP "Ford" cap it works fine and when I put Ron's cap on it also sealed. I ran the jeep for 30 minutes in the driveway and the temp held at the thermostat temp of 170 deg F. Nothing came out the over flow tube. The thicker washer blocks the bottom 1/3 of the overflow tube, but there is still plenty of open space.

Anyone see anything wrong with this solution?? I'm still curious why my filler cap neck seems so deep.

Here's a shot of the two caps and the filler neck with the new gasket.
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IMG_3954.JPG (118.79 KiB) Viewed 105 times
Doug Thom

Chassis GPW 84536 - DOD: December 9, 1942 Dallas, TX
Engine GPW 89702 - early January 1943
Hood Number (est.) 20192259
MVPA 34210, MVCC 12569


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Re: Coolant system testing

Post by artificer » Wed Sep 19, 2018 12:04 pm

Doug wrote:Anyone see anything wrong with this solution?
I see a problem in that the cap with too thick a gasket will have a pressure that is unknown & too high.
If about 7psi [the pressure cap I used to run with] OK but higher not recommended.

Mike is right about sealing the overflow. Fit a vacuum cap with clamp over the end of the overflow tube https://www.supercheapauto.com.au/p/gos ... 20597.html
Remember to remove the cap/plug though.
Doug wrote:when the thermostat reaches temp and opens I'm dumping a quart of coolant out the over flow tube.
Be aware this is normal if the top tank is overfilled before driving, as most people insist on doing.
Correct level needs to be about 2 knuckles under the bottom of the neck.

The only time to worry is if coolant keeps being discharged after that initial dump.
Just don't re-fill BUT ensure the hoses feel tight to squeeze, when the engine is hot.
If hoses are tight it means the system is absolutely full of coolant.
When hot if the hoses are not tight to squeeze, it means the following:
1. The radiator cap is not sealing
2. the system is NOT full of coolant, usually can only be a result boiling if not 1.

Don't remove the cap if no evidence of boiling or if the hoses are not tight, when they should be.
Removing the cap @ any time especially when hot extreme care as non boiling coolant will likely boil when pressure is removed & super heated steam causes severe burns.

Understand when hot the 'expanded' coolant fills everything including the top tank. When the coolant cools down the vacuum valve in the radiator cap opens & lets air into the space in the top tank. No valve & vacuum would cause the tank to collapse.
https://www.freeasestudyguides.com/engi ... r-cap.html

I ran into a situation in the late 60's where the radiator neck was deeper than it should be. This meant the spring loaded radiator valve/seal [governs cracking pressure] was not effective.
One should be able to feel the slight resistance of the spring when fitting a radiator cap in the neck.
That is when one has to push down on the cap before turning.
If not, it would be the same as running with a loose or similar cap to the one I suggested be made into a pressure tester.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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douglasmthom
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Re: Coolant system testing

Post by douglasmthom » Sun Oct 07, 2018 11:09 am

Hi guys,
Sorry to be absent on this - I was traveling....

So my typical cold fill level is to the bottom of the baffle which is more than two knuckles, so I don't think I've been over-filling.

As for the thicker washer creating too high a pressure - I understand the concept. However, I think I was having the opposite issue in that with the thinner washer, I was getting NO spring displacement in the cap when depressing it before screwing it in place. Now with the thicker washer I can feel the displacement, albeit the release pressure is still not known.

I'll try and rig up some some way of pressure testing the system so I can see when the cap actually releases the this thicker washer. I don't know what else to do.

As, always, I welcome your comments.
Doug Thom

Chassis GPW 84536 - DOD: December 9, 1942 Dallas, TX
Engine GPW 89702 - early January 1943
Hood Number (est.) 20192259
MVPA 34210, MVCC 12569

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Re: Coolant system testing

Post by Ben Dover » Sun Oct 07, 2018 11:55 am

I would start with a dealer who has exact fitting replacement parts. Or install a Gates or AC 4# cap with the rubber seal made to it. Original caps can still be found that require the gasket in the neck. All are reliable. And remember, if your cap has a rubber seal on he valve, do not install a gasket in the neck.
The correct thickness of the OEM Radiator Filler Neck Gaskets is 0.062" (Fibre)", and 0.066" Thick for the Rubber Gasket. Fibre comes in red, Gray, or Black, and Rubber seems to be Black. These fit the MB/GPW, CCKW, M-38/M-38A1, etc..
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