tm9-801.com

We are trying to help a guy fix his cooling problems on another site (http://hmvf.co.uk/forumvb/showthread.ph ... post295607).

I brought up that he needed not only a radiator cap, but a GASKET to seal the cooling system (is this related thread: http://hmvf.co.uk/forumvb/showthread.ph ... ank-Bottle ).

First, I was astonished that many CCKW owners DIDN'T KNOW that you needed a gasket, and then when I checked MY radiator car, low and behold, I didn't have a radiator cap gasket! I've not had much trouble with engine temps... but I don't drive my truck that often either.

So everyone loosing water from the radiator overflow... check to make sure you have the gasket for the cap!

"....So everyone loosing water from the radiator overflow... check to make sure you have the gasket for the cap!..."

If coolant comes out of the overflow tube/hose it is not from a bad or missing gasket in the top of the cap.

The cap has (should have) a spring loaded inner seal that contacts the "step" in the bottom of the filler neck. This is usually a brass disk and it keeps the coolant in the radiator . If it seals as it should coolant cannot come out of the overflow tube unless....the pressure in the cooling system is higher than the cap's designated pressure release rating.

If the pressure in the system exceeds the caps capacity then the disk will lift and release pressure (steam and or coolant) .

When that happens the pressure will go out the overflow tube. If you do not have a gasket some may come out the top of the neck as well.

Usually, when CCKW "pees" out the overflow it is because of:

Overfilling the cooling system
A cap that has a defective disk assembly
A cap that is not of the proper pressure rating.
A cap that is not of the proper depth for the radiator.

The radiators in old vehicles such as the GMC have a deeper neck than many newer ones. Using a cap that is not the proper depth will cause coolant to leak.

You must use a cap that is the proper depth and pressure rating for the CCKW. Most caps look the same but only the correct cap will work correctly.

BTW we have driven many GMC's many miles with caps that do not have gaskets and have had no problems with leakage as they are correct caps for the vehicle.

Of course ...having a gasket won't hurt but it's not critical....

Jim Gilmore

Um, if the gasket is not installed you will not develop any pressure in the radiator. The seal you are talking about is ABOVE the overflow tube. Metal on metal is not going to make a seal. That lack of pressure will allow the water to boil, and expand up and through the overflow tube.

"If coolant comes out of the overflow tube/hose it is not from a bad or missing gasket in the top of the cap." You are repeating what I said The gasket is the only seal to hold the pressure in the radiator. Run your truck without a cap and see how much water spits out. It will... the boiling water will find its way up and out. But the gasket is INSIDE the neck, and the cap does sit on it.

"The cap has (should have) a spring loaded inner seal that contacts the "step" in the bottom of the filler neck. This is usually a brass disk and it keeps the coolant in the radiator . If it seals as it should coolant cannot come out of the overflow tube unless....the pressure in the cooling system is higher than the cap's designated pressure release rating." No. The seal under the cap will not hold the full radiator pressure because IT WILL NEVER SEE IT! The overflow tube will vent pressure out.

"Overfilling the cooling system
A cap that has a defective disk assembly
A cap that is not of the proper pressure rating.
A cap that is not of the proper depth for the radiator."

Only the last one has any merit.

"The radiators in old vehicles such as the GMC have a deeper neck than many newer ones. Using a cap that is not the proper depth will cause coolant to leak."
The SNL lists 3 cap and core combo's for CCKWs, but without chassis numbers or engine SNs or why they are paired. No mention of why

I'll add this snippet:

"Hmm....I think we need to learn a bit more about how the radiator cap works. If the gasket in the NECK of the radiator is between the CAP and the Inner ledge of the neck then that is where the pressure seal is created, if my understanding of the radiator cap is correct, then it is the EXPANSION of the coolant (not the temperature) to the 4 lb+ threshhold the opens the cap/gasket/neck and allows coolant to rise higher in the neck of the radiator. The thin brass disc has sealed the CAP to the TOP of the radiator and thus the expanding coolant has only the overflow tube available to expand into.

So I am of the opinion the the PRESSURE in the radiator and in the cap is not created by the brass disc, but by the gasket down further.

Therefore if your brass disc has a crack in it, the PRESSURE seal of the cap is not effected since that is a function of the gasket, the lower part of the cap and the ledge down in the radiator itself. If there is a crack in it, the worst that would happen is the possibility that when the pressure in your fadiator exceeds the 4 lb cap, the coolant will not only have the option to escape via the overflow tube, but it MIGHT also escape between the cap and the edge of the radiator where the brass disc is mounted.

The point being....the brass disc has nothing to do with actual SEAL the gasket provides between radiator neck and cap. If it is not what seals the system, then it is not what maintains the pressure in the system."

http://www.g503.com/forums/viewtopic.php?f=4&t=187068

I guess this will have to turn into story time, instead of ppl reading the TMs

TM10-1563 March 20, 1943 page 05-4

7. Radiator Filler cap

A.(...) The first stage raises vavle from special rubber gasket in filler neck...

Your brass whatever directly under the cap, as I have stated, has very little to with anything..

"....You are repeating what I said The gasket is the only seal to hold the pressure in the radiator. Run your truck without a cap and see how much water spits out. It will... the boiling water will find its way up and out. But the gasket is INSIDE the neck, and the cap does sit on it..."

A CCKW runs at 180 degrees if it has the PVC type crankcase vent. About 145 degrees if it has the earlier venting. Much less temp than boiling water.

Jim

No, it will only run at 180F if the thermostat is working correctly and with proper airflow through the radiator. Water will evaporate much quicker without a sealed system. Water doesn't need to boil in order to evaporate. Water will evaporate at room temp. The engine is completely capable of making the water hotter than 180F. I find it humorous, nay, HI-LARIOUS that you think that the coolant temp is what the gauge says it is... in every part of the system.

Let me borrow your CCKW... I can make that water boil without a cap quite easily.

I'm starting the think that you are, as I have been warned, Bendy Dover in disguise.

"......when I checked MY radiator car, low and behold, I didn't have a radiator cap gasket!......"

When I read this it appeared you were saying the car (cap?) had no gasket...and of course the CCKW cap does not have a gasket as newer caps do (they usually have two). I see now that you were referring to the radiator filler neck gasket I believe...and this is an item that was on the vehicle when it was built.

Nearly every CCKW I have driven, worked on or checked the coolant level was missing this gasket. And every one never had a problem with overheating or losing coolant out the overflow (except for one that had a clogged radiator...but that's another story) . But..as you say there should be one and it won't hurt to put one in. The only CCKW rad neck gasket I have seen was a fiber type like the seal on the fuel filter bowl. This is most likely the later type listed in the ORD-9 as most MFG's were asked to conserve rubber any way they could.

".....No, it will only run at 180F if the thermostat is working correctly and with proper airflow through the radiator...."

Isn't this what I said? You don't drive your CCKW with a defective cooling system do you? We don't.


"...Water will evaporate much quicker without a sealed system. Water doesn't need to boil in order to evaporate. Water will evaporate at room temp...."

Yes, of course , but I never said anything about evaporation. How long will it take for the water (we use coolant ) in a CCKW cooling system to totally evaporate? ...just wondering.

"....Water doesn't need to boil in order to evaporate...."

Well, of course.....that's why a CCKW (and jeep, Dodge and other WW II MV's with the PVC system) must use a 180 degree thermostat !

"....The engine is completely capable of making the water hotter than 180F...."

What temp does your CCKW run at? Does it run hotter than 180 when you drive up and down the Pennsylvania hills or is it cooler when out on I-80?
The one I drive most often runs right about 180 at speed (50 mph + ) on I-80 in the summer.


"..... I find it humorous, nay, HI-LARIOUS that you think that the coolant temp is what the gauge says it is... in every part of the system...."

You do? strange...because I never said anything like that. I said " A CCKW runs at 180 degrees if it has the PVC type crankcase vent......."
But....if you want to talk gauges....I test the temperature gauges in the vehicles I restore and drive. Even if it is a new gauge it is tested in boiling water alongside a precision laboratory type thermometer to be sure the gauge is accurate. On vehicles with the gauge already installed I used a laser thermometer to check them.

Does the gauge on your truck not indicate the correct temperature?


"....Let me borrow your CCKW... I can make that water boil without a cap quite easily...."

I don't think I said anything about running without a radiator cap.... But...it would be interesting to see. Could we use your truck instead? I would have to drain all the coolant out to replace it with water in the one I drive most and I'm too lazy for all that work.

"....I'm starting the think that you are, as I have been warned, Bendy Dover in disguise....."

You think I'm Joel Gopan ? !!
You are paying me a great compliment! I only wish I knew half as much about military vehicles as that guy .

Nope, I'm me, that's why I post under my own name and not some made up one.

Jim Gilmore

Seeing that there already is a jgilmore account I gotta ask if you are not the same guy, why sign up under a similar name? I'm not going to waste time checking accounts (I can easily find out who is who).. but I'm not the only one noticing some similarities.

I agree that Gopan has some knowledge.... but getting it out of him in a useable format is the problem.

Without that gasket you are going to run low on water. Now you may be adding water more often than you realize, or it may be so low that its not able to overflow anymore... but you heat water, and don't contain it, its going buh-buy.

So you cracked open the gauge to bend the Bordoun tube linkage to get the needle to match the laboratory accurate thermometer? Really? Since the gauge only has a 180 and 220 mark, where is 212F exactly?

I'm kidding... the gauges are pretty accurate.. well, if you peg it, its to hot.. if the needle doesn't come off the peg, its broke.

Ether does give you a good buzz.

"....Seeing that there already is a jgilmore account I gotta ask if you are not the same guy, why sign up under a similar name? I'm not going to waste time checking accounts (I can easily find out who is who).. but I'm not the only one noticing some similarities...."

Yep, I think they are both me.....I registered some time ago but when I decided to stop "lurking" and post I couldn't remember my username/password so I just started a new account.

Jim Gilmore

Jim Gilmore wrote:
“Nearly every CCKW I have driven, worked on or checked the coolant level was missing this gasket.”

This prompted me to check my truck and low and behold there’s no gasket! I’ve driven this truck to many functions including the MVPA convention in Dayton Ohio, a 1200 mile round trip pulling a 57mm anti-tank gun and a weasel in the bed. The temperature stayed at 180 pulling 19,120 lbs. gross weight up the hills of western Pennsylvania and I never lost a drop of coolant.

Also, for those who believe “metal to metal is not going to make a seal” how do you explain intake and exhaust valves sealing on the seats?

WHat is the water level in the radiator?

It should be visible from the filler.. or is it lower that than?

My truck didn't have the gasket, and I suspect that the water level was 4-6 inches low... I could not see fluid from the filler. If I filled it up to the filler, I would spit water out the overflow for a while. Now I know why.

Pfarber wrote:
“WHat is the water level in the radiator?”

“It should be visible from the filler.. or is it lower that than?”

Looking in the filler at an angle one can usually see the level. However if the level is a little lower it can’t be seen. Using a hydrometer something like a dip-stick you can pull coolant from the tank and get an idea of the level.

Also from Pfarber:

“My truck didn't have the gasket, and I suspect that the water level was 4-6 inches low... I could not see fluid from the filler. If I filled it up to the filler, I would spit water out the overflow for a while. Now I know why”.

With or without the gasket if you over fill the radiator coolant will come out of the overflow.

As per TM9-801, page 41, section17, paragraph c, sub-paragraph b, Filling Radiator:
“If engine is cold, a loss of approximately one quart will result. If engine is warm, no appreciable loss will be noticed.”

Sub-paragraph c Use of Anti-freeze Solutions:
“When engine is stopped and water cools, contraction of liquid lowers level. It is this apparent low level which might indicate the need of additional fluid. Water in system should be hot before any check of level is made”

As per TM9-801, page 41, section17, paragraph c, sub-paragraph b, Filling Radiator:
“If engine is cold, a loss of approximately one quart will result. If engine is warm, no appreciable loss will be noticed.”

The top of the radiator is basically open.. no tubes. It can easily hold a quart of expansion unless you fill right to the neck... which the TM says to only fill till coolant is visible.

Also, the radiator cap only controls the amount of PRESSURE in the radiator. It doesn't care about the temp, level or even if the water pump is circulating.

Now if the radiator was completely full, and the engine run... the pressure will rise and the water expands (assuming the gasket if there and the cap is not continually venting the pressure).

This all all to easy to prove. Fill your radiator, make sure the gasket is removed, install the cap, run the engine... and be amazed that water is coming out of the overflow tube.

It will if the gasket is not there, the pressure will always vent (as there is no seal) and take water with it.

Milspec wrote:

"..With or without the gasket if you over fill the radiator coolant will come out of the overflow. .."

"....As per TM9-801, page 41, section17, paragraph c, sub-paragraph b, Filling Radiator:
“If engine is cold, a loss of approximately one quart will result. If engine is warm, no appreciable loss will be noticed.”
Sub-paragraph c Use of Anti-freeze Solutions:
“When engine is stopped and water cools, contraction of liquid lowers level. It is this apparent low level which might indicate the need of additional fluid. Water in system should be hot before any check of level is made”



Pfarber wrote:

(Quoting me)

"Overfilling the cooling system
A cap that has a defective disk assembly
A cap that is not of the proper pressure rating.
A cap that is not of the proper depth for the radiator."

"Only the last one has any merit. "


I think Milspec has proved me right on the first one.

He is correct about filling the radiator and driving the vehicle. I have had it happen before and now check the coolant only when the motor is operating temp. His trick of using the hydrometer is a good one and I'll try that next time.



Pfarber also wrote;

"...Now if the radiator was completely full, and the engine run... the pressure will rise and the water expands (assuming the gasket if there and the cap is not continually venting the pressure).
This all all to easy to prove. Fill your radiator, make sure the gasket is removed, install the cap, run the engine... and be amazed that water is coming out of the overflow tube.
It will if the gasket is not there, the pressure will always vent (as there is no seal) and take water with it...."

I'm not sure you read Milspec's post completely....

He already said that if you fill the radiator full and run the motor it will come out the overflow...and it will whether you have the gasket in or not.
The TM states this as well. This is why it tells you check the coolant after the motor is warm.

Milspec says he has driven long distances without a gasket and had no problems. I don't know about him but I can tell you I have driven from the East PA border to Fort Lee VA. (and back) in a CCKW LWB cargo that did not have the gasket and I never had a problem with the coolant or overheating.

Of course I will put a gasket in the one I drive most..not because it has a problem but just because it's supposed to be there....

Jim Gilmore

And in doing so how low did the coolant level go?

I can tell you in a jeep if you leave the gasket out you will not see coolant at the proper level (which is roughly defined as visible in through the radiator neck).

Next time you fire up the truck, take the gasket out and run it in a parade, or put a 100 miles on it. Check it and tell me (or better yet, document it with photo's) how low it goes.

I find it funny that everyone magically seems to recall the level of coolant in their radiators. Heck a few days ago most didn't even know about the gasket.