Ok, so the weather has changed and I haven't been driving my truck much... so, I drove it today and it blew out most of the water.

It didn't get hot. When I stopped, there wasn't any pressure in the radiator. Two minutes after shutting it off, I filled the radiator with water. Not even steam came out when I did so.

You can fill it full, it won't lose any water until you drive it at highway speed for a few miles and come to stop. When you do that, it blows out a gallon of water. But the temperature never rises on the gauge, and when you get stopped, you can touch the radiator without blistering yourself, and there's no pressure.

As long as you don't drive slow or run real hard in a low gear uphill, it doesn't lose any water. Even if you are pushing it WOT at 3800 it only loses a little water and... the temperature gauge never rises.

I filled it back up, let it run for 10 minutes fast idle long past when the thermostat opens. The water runs clear (no foam, no apparent trapped bubbles, it doesn't "rise" and overflow or anything like that.

I got a new radiator cap, because the old one has a bad gasket... and it got VASTLY worse. Still, what confuses me is that I stopped to do something with the hood open... and it belched water out from the under the radiator cap... and it didn't burn me.

I can't find any evidence of leaky head gasket. It doesn't overheat. The water seems to circulate well even at idle.

Any ideas?

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

Possibly a cracked head/block - compression or exhaust gas is getting into the cooling system one way or another. Try a block testing kit (one of those gizmos you hold over the rad that changes color in presence of exhaust gasses) and run a compression check. Oil level / color is normal on the dipstick?

Have you checked to make sure all your radiator hoses are connected tightly? Depending on how long it's been sitting, maybe your lower hose is rotted and the leak only really opens up under high speed? Also check the smaller hoses coming from the water pump, like the small 2-3" hose that goes straight up to the head.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Ok, here's what I now I know. The new cap I bought is defective. Doesn't seal AT ALL - will not hold pressure and it lets the water out from under the cap, doesn't seal so it can pull back out of the overflow. I got it in the evening, put it on in the dark. Don't know if that's why it belched out the water so fast. The old one has a bad gasket, so it didn't seal right, either.

So, I got a different brand - and it will hold pressure now, but haven't had time to drive it and see if it's actually fixed or if there's more going on.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

How could a cap be defective to the point it lets water spew out? Unless the gasket was completely missing...

Cap leaking or otherwise - If the water was cool enough to not burn you, and there was enough pressure in the system so it "belched out" - then I still say pressure is entering the cooling system when it shouldn't be.

The gasket doesn't even touch anything. That's how it leaks.

But, with the new cap, it still builds pressure and eventually shoves out water.

So, I guess I have some problem.

When I shut off the motor, I hear something in the head going making a steady bubbling sound. So, I guess I"m going to pull the head and see if the gasket appears to have any bad spots.

If not, I guess I'll have to replace the head, which is gonna hurt, because I don't have the money to rebuild a new head to my old specs - which is shaved over .100 to raise the CR, Stainless engnbldr oversize valves, bronze guides, etc.

And no, there is no water in the oil, no antifreeze smell in the exhaust, it runs very good.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

65CrewCabPW,

My 74 Dart did this exact same thing when I got my new radiator. I went through about 6 caps thinking they were defective. After watching the water spew out once again, I decided to take a straight edge to the radiator filler. It was way off, not flat, like someone dropped it on the tank up side down and bent the filler. I never thought to look at that....

I pried and pounded it out very carefully and soldered the rest to make it flat. I would sand and soldier, sand and soldier, like doing body work.....until the neck was nice and absolutely flat with a good sealing surface.

No problems since I leveled the filler top. All caps work fine.

Hope this helps....

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Check the thermostat. It may be stuck closed, or in backwards. That could let the water in the engine overheat, and build pressure, but the radiator still be cool/cold.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

It holds now with the new cap.

I replaced the radiator two years ago, and the cap worked fine until apparently last fall when the rubber parts began to fail. I just didn't realize it.

The new one that's defective is somehow made too short, so that the spring loaded part doesn't even touch anything.

The second new one works fine. Except that the pressure in the system eventually overrides the cap and it has a steady stream of bubbles into the overflow tank when it's been going down the road.

If you stop and let it idle, the bubbles slow and eventually stop. It won't get above 180 unless it pushes out so much water there's nothing to circulate (a gallon low).

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

X2 what he said. do you get heat from the heater in the car??

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Mattelderca
78 NYB (gone now), two S series, three old Snow Cruisers and a Doo.

If I remember correctly, was this the truck that you had detonation problems on earlier? If so then it's very possible that you have damaged the head gasket & it's pressurizing the cooling system. (I'd use a block tester before tearing the head off)

Another distant possibility is that the lower rad hose is sucking flat at higher rpm & boiling the block- doesn't explain the "cold" rad spewing, BUT straight H2O (if that's what you're running)- water boils much lower temps than a 50/50 antifreeze mix.

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63 Valiant Wagon
225 - 4 bbl

Yes, water circulates normally.

I'm quite sure now I'm getting some kind of leak of combustion or compression into the cooling system.

It's a steel shim gasket, so I'm kind of surprised, unless, of course, there's actually some problem with the head itself.

And... NO LOCAL PARTS HOUSE HAS A HEAD GASKET.

GRRRR. needed to fix this ASAP.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

Do a compression check at a minimum before starting to buy parts. That way you'll at least know what cylinder(s) to look at once you do have it apart.

Sorry for the delay, I was busy for a week, the head gasket had a small "rusty" looking area between cylinders 4 and 5, and I do think it was leaking there. Remember, it was a shim type gasket, and it appeared that it was leaking just a little. It also appears that it seeped water ever so slightly at times.

Anyway, I'm having the head re-trued (not that I think there's actually any issue, but milling a little to make up for the thicker gasket) and going with the regular gasket instead of the shim style.

I originally used the KW copper stuff on the shim head gasket, but it didn't seem to help. It still started leaking.

Anyway, I hope the newer technology gasket holds.

What's interesting, is the appearance of my head and cylinders, from running propane. It has a light tan coating of deposits, no black anywhere. I believe the deposits are from the small amount of oil that sometimes comes through the PCV and breather. I'm using an aftermarket chrome valve cover which has no baffles (don't remember if the original did, either), and there's a thin oil film emerging from both that goes into the intake and is spread throughout the intake.


I'm not happy with the chrome rocker cover, I can't get it to stop leaking... The original is rusty and dented and bent. I'd like to get it to stop leaking, as I hate the mess under the truck.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

Use a rubber gasket on the valve cover and install a oil/air separator then you won't have any more oil coming from the PCV.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG