The GMC CCKW

I know the post is long, but I wanted to put all of the info out there so I could get some good guesses.

I have a 1945 DUKW that I run almost daily for the last year and a half.
It's slowly got to a point where I can only run it for 15 minutes or so before it starts to overheat. Just running it at a grand on the tac, it will start getting too warm.

It runs and sounds absolutely perfect. Doesn't act like it's running lean because I have full power- maybe running a tad too rich as I can smell a little gas.

Here's some repairs that I've done over the last year- maybe something will ring a bell with someone as to why it's overheating now and not previously:
Had radiator cleaned out last August
Waterpump went out in April- replaced
Hydrovac was pumping brake fluid into intake- May
Replaced head gasket in May because I thought that's where the smoke was coming from before realizing that the Hydrovac was the problem
Running "jerky" so I had the carb gone through- 2 weeks ago.
New thermostat, adjusted idle and corrected timing- Today

It's a tiny bit better, but it still got up there. If it's idling, it will stay cool, but as soon as you start driving it and puting a grand on the rpm's, it will start creeping on me.

Here's what I'm going to try next one at a time and then run it to see if that did anything.
Tighten fan belt - A little loose and I'm wondering if it's slipping at higher rom's and the water pump isn't operating properly.

Increase my fuel regulator in case it's not getting enough and running lean at higher rpms.

Take the radiator out and have it cleaned and tested.

Get a new Governer- Maybe it's faulty and making it run lean?

Putting in a new waterpump- Maybe this one has gone bad already?

Any other thoughts or things to check? I've gone through the books and I believe I've covered everything, but maybe someone has run into a similar problem?

Thanks much guys!

You have done a cylinder compression test ? what were the readings ?

Is the thermostat opening all the way?

Do you have the original style radiator cap?

Is it just the gauge that is running high or is the coolant above temp specs?

Does the coolant temp match the gauge temp?

Has it boiled over?

You have done a cylinder compression test ? The head was gone over and tested by a well respected WWII Jeep specialist. I don't personally know what the readings were, but he's satisfied that it's not that.

Is the thermostat opening all the way? Even without the thermostat in there- same problems.

Do you have the original style radiator cap? A Napa replacement.

Does the coolant temp match the gauge temp? Not sure how you would tell?

Has it boiled over? No it hasn't, but it does try and diesel upon shutoff and makes a sound that I liken to a huge "sigh"

If it was eating brake fluid (remember this if you are running silicone...), did you clean the check valve out? It is/was probably all gummed up from the fluid AND not working correctly. In addition, you "could" ruin the new booster

NOTE: Burning silicone brake fluid created silica like particles which are not good for cylinder walls....

Here are a few more thoughts
Improper timing will lead to higher operating temperatures....You did say it diesels.?????
Any chance your radiator core is partially plugged ( from inside)
Do you have the CORRECT duck fan? I think it is supposed to push instead of pull.

Hope this helps
John

just adding in a comment.... I ran into a cooling problem with one of my Dodge 3/4 WCs. We replaced the radiator, water pump, thermostat, etc.... well, then we got 'smart' and flushed the block with some stuff from the autoparts store - it cured the problem. Well, it was really dumb of me not to do this firest but at least I now have a new cooling system....

We use regular DOT 3 brake fluid from Napa- not sure if that is silicone or not.
The timing has already been re-checked and is dead on. It runs perfectly except for the whole getting hot thing.

The radiator was done last August- that is one of the possibilities although it shouldn't with just a year passed.

It's the correct Dukw fan and the same one one we've been using over the last couple of years without an overheat problem.

Well at least our "kicking" this around has eliminated some possibilities.


John

Yea- the more ideas the better. Maybe something will click.

Well inview of so many known unknowns, I'd start with a radiator pressure leak down test. 24 hrs. Then I'd run the cold engine and see if, or how quick, and to what level the rad pressure rises to. Sure is better than 2nd quessing.

If this is a new installation of a thermostat, If the thermostat does NOT have a hole in it (little one), I drill a small hole near the edge (1/16 max). Sometimes (more times than I care to count) with the thermo closed, you get an air pocket under the thermo and with air only up against the thermo, it will not open! The small bleed hole will let the air out and allow the hot coolant to "touch" the thermo and allow it to open. This also happens if you drain the coolant.

I checked function of the thermostat last time this way:

1. completely drain the water
2. refill while engine was cold up to max, so that the water is visible in the radiator.
3. Start engine, drive around until the engine heats up to its normal operational temperature.
4. Check if water in radiator is still visible. If not, thermostat has opened and everything is okay.
5. Add more water until level is visible again. ( I had to add almost 2 Litres).

Regards,

Chris

Hi Guys

I also had a cooling problem a couple of years ago, tried everything like you. But nothing seemed to help. At the end a friend offered one
of his NOS radiators he has, since then no problems. Temp is
always between 185 and 190, no matter what conditions.

Corné

Does the rad get hot?

apart from the suggestions from previous posters

try removing the thermostat completely

u can also try idling the truck in front of an industrial strength fan (if u have acces to one), or temp fitting an electric fan.

u can check yout thrmo and temp gauge by bringing to boil on stove with a thermometer.

that may give u some clues.

it is possible your blocks water passages are sedimented

or your water pump is cavitating due to impellor problem

Update- took the water pump off and made sure it was ok and put it back in and filled up with 50/50. When I started it up, I left the rad cap off and watched it. Coolant just sat there until it reached the thermo temp and then it started overflowing out the radiator cap hole. That's what it should do correct? Also, when I pulled the lower rad hose off, coolant came flowing out. That means it's circuulating doesn't it?

Anyway, I took the radiator out and have it at a shop to check it out. I'll get it back tomorrow and see what's doin.

After that, my only other options left are replacing the radiator completely and then pulling the head to make sure the water jets aren't being blocked. I sure hope it's the radiator so this will be over!

We do a lot of cooling system design and system testing and trouble shooting in our Cat engine business.

The first rule is "beware of preconcieved ideas". Avoid throwing parts at a problem. There are simple tests that can be done with expected results that will point you to different root causes.

But before we launch into the "what and how" of trouble shooting the automotive cooling system, let me recommend the you study the cooling system components as they are currently installed in your DUKW. Especially the fan and water pump and their relationship to the fan shroud on the radiator.

The fan on the CCKW truck is a 5 blade suction fan. The inside or concave curve of the fan should face the engine block on the CCKW. The notch on the blade goes toward the engine block. Look at the edge of the fan. The fan blade should set in relationship to the shroud with approxamatly 1/3 of the blade inside the shroud and 2/3 of the blade width outside the shroud.

Now look carefully at your DUKW fan and water pump. The fan on the DUKW is different. It should be a FOUR blade blower fan. The concave side of the blade faces the radiator. IF the fan is installed backwards it will become a very inefficient fan that will move some, but very little air. Next look at the relationship of the fan blades in the fan shroud. The water pump for the DUCK is also different than the truck water pump. The DUCK pump has a longer "nose" that bspaces the fan correctly into the shroud. And it has a hex nut in the middle of the hub plus the four capscrews. There is supposed to be a spare fan hub spacer stored on the bulkhead in the DUKW engine compartment on the left side near the overflow tank. The spacer is to be installed on the truck water pump if a "long nose" DUKW replacement pump is not available.

Wrong fan or one installed backwards plus a short nose CCKW pump without the spacer installed on the end will result in the symptoms you describe.

Check those componets before we start on "trouble shooting lesson II". Tell us what you find.

Cat Man I

The fan was in correectly and has the spacer for the waterpump putting the fan next to the radiator. It worked perfectly for a year and a half.
My overheating problem is new. I tried a higher power electric fan as well.

So what were those Hot and Cold compression readings ? How was the leakdown test ?