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.

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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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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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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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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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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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Re: Coolant system testing

Post by douglasmthom » Sun Oct 21, 2018 3:36 pm

Here was my test set-up. I plumbed into the radiator drain with 1/4" pipe, and a tee with a tire valve and a barbed hose fitting for a pressure gauge.
I hooked the tire valve to a bicycle pump and put the pressure gauge on the ground where I could easily see it. Then I put a rubber tube on the overflow tube of the radiator and put it in liquid (radiator fluid) so I could see if it bubbled. The coolant had been drained from the engine

Then I air-pressurized the system to convince myself that I had a cap that was leak tight but released at around 4 psi. The AJP radiator cap with a metal bottom in conjunction with a .062 fiber washer was the right combination. The hose on the radiator overflow would start to bubble between 3.5 and 4 lbs.

So then I filled the engine/radiator with coolant and fired her up. I also removed the hose on the overflow so I could look for any discharge. The engine heated up normally in the driveway and I watched the pressure gauge. I could see the pressure drop when the thermostat open and then when everything stabilized I was running about 3.5 psi with an occasional drip from overflow tube. I thought the test set-up worked pretty well.

So I plan to take off all the test gear now and road test her.
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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 » Mon Oct 22, 2018 5:05 am

artificer wrote:
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.
________________________________________________________________________________
The Fuel Sump Caps as installed on the MB/GPW are not made to hold pressure, they are a non-pressure cap, there is no valve in them to seal the bottom of the filler neck. They are not made to withstand any pressure and that is why 30's-40's Ford owners with radiator coolant leaks installed them.
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Re: Coolant system testing

Post by douglasmthom » Mon Oct 22, 2018 7:54 am

Before I tried the set-up shown I did try the fuel sump cap. It would not make a seal on my radiator.
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 » Mon Oct 22, 2018 10:06 am

And the MB/GPW Tank Well Drain Cap was never intended to hold pressure, they were originally marketed as an optional zero pressure Radiator Cap for cars/trucks starting in the 30's.
2011 MVPA PIONEER AWARD - MVPA #1064
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
LIFE MEMBER AM LEGION-40/8-DAV
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Re: Coolant system testing

Post by artificer » Mon Oct 22, 2018 1:01 pm

Comprehension is certainly a skill missing in action!
Give it a rest & stop misquoting me, please!
I did say
John wrote:Just get an old non pressure cap that fits the fuel tank drains on a G503
Joel wrote: The Fuel Sump Caps as installed on the MB/GPW are not made to hold pressure, they are a non-pressure cap, there is no valve in them to seal the bottom of the filler neck.
Who said there was a sealing valve on the sump caps? Certainly not me!
Plus a full blown radiator cap with the valve/seal can also be used.
Just remove the spring loaded sealing valve & retain the brass sealing ring that fits on the top of the radiator neck.

Tell us what was used to seal the top of the radiator on the desert modification, overflow tank setup?
The same cap as on the fuel tank well, was it not?
The brass ring that seats on the top of the radiator neck, so they did seal & they do hold pressure so overflow goes to the front mounted reservoir with the regular cap. If I'm wrong I, as always, will admit so.

Doug, if the cap didn't seal on the top of the radiator neck [for testing] use a correct diameter rubber seal out of a plumbing package of toilet gaskets from Home Depot but the brass ring should act as a good enough seal.
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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Re: Coolant system testing

Post by Ben Dover » Tue Oct 23, 2018 6:57 am

The "Sump Caps" do not seal pressure, they keep water and dirt out of the sump. They are WO- A-3055, I have several NOS and Used in front of me they cannot be adapted to pressurize any radiator filler neck.
The Sump drain wells are not made the same way as a Radiator filler neck, take a look and hopefully you will understand why your suggestion is not possible. Have you ever attempted to drill out a sump drain cap for a tubeless tire valve, try it and explain why you discovered it is not possible.
2011 MVPA PIONEER AWARD - MVPA #1064
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
LIFE MEMBER AM LEGION-40/8-DAV
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Re: Coolant system testing

Post by artificer » Tue Oct 23, 2018 3:12 pm

Doug has successfully diagnosed/tested & his topic "TESTING" has been fully addressed.
I stick by what I said in the 1st answer to his question by using an old cap [sump or radiator with valve removed] to make a tester & yes I have done this before. Also used the same method to manufacture a pressure brake bleeder.

https://www.augum-parts.com/store/en/pr ... p-cap.html
Click on the picture for underside view of the cap & see how easily the centre can be drilled out.

The reason this cap doesn't pressurize the cooling system [is called pressureless] is because the overflow tube is open.
The gasket [not brass in this case], clearly shown in the link, SEALS/CLOSES the radiator neck top.
Close off the overflow tube & of course the system can be pressurized.

This 'overflow' issue was correctly identified by a practiced tradesman Mike W. early in this thread.
Alternatively the overflow tube can be the pressure source for testing when this type cap is fitted.


https://www.1942mb.com/article/111/MB-G ... nk-Install
The desert overflow system uses the same fuel tank sump seals/caps to advantage by directing this overflow to an external reservoir fitted with a standard 4# pressure radiator cap. If this pressureless cap did not seal the hot coolant would take the easiest path of resistance & spew out the top of the neck. It certainly doesn't but firmly seals!
John wrote:Doug, if the cap didn't seal on the top of the radiator neck [for testing] use a correct diameter rubber seal out of a plumbing package of toilet gaskets from Home Depot
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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