VW - did it always overheat, even before engine rebuild, or did it begin overheating only after the rebuild?

Unreg - how would you describe the smell of compression leak into the coolant ? smell like tailpipe, gas, chicken, or what? would that leak always show up on a compression test as one cylinder lower than the others? or not.

 

I'll recap for everyone what I've been through with this overheating problem:
Rebuilt engine
New Heads (cast iron, aftermarket)
Two thermostats (one with a bleeder hole, both tested in boiling water)
Two radiators (started with a 2-core brass, reverted to a stock, 1-core aluminum)
Two water pumps (started with a rebuilt, switched to a new unit)
Radiator cap replaced and properly sized
Clutch Fan was replaced as the old one was bad
Torque on the heads double-checked after 1,000 miles on the rebuild
Pressure tested the radiator/cooling system -- holds pressure

It's a real stumper when it'll run hot. I've monitored the outside temperature to determine if that's a factor, and it isn't. I can guarantee that if I load the bed with a few hundred pounds or drag the trailer, it will run hot. I can drive it around later this week and then smell the coolant; however, any other time I've topped it off I haven't smelled anything.

I didn't drive the truck much before the rebuild and write off any issues it may have had due to how badly maintained it was. It started blowing coolant on my first road trip when I hauled the trailer loaded with a Beetle body along with two engines and transmissions to Alabama. That was about 5 weeks after I had rebuilt the engine and broke it in. From there, it's been consistent -- haul a load, blow coolant.

 

No, I heard that it smells like fish, but it tastes like chicken.

 

VW,
Man it sounds like your just going round and round with this thing. So you checked all the cooling system front to back. This is what I'm thinking with out seeing the truck: Oil cooler, Trans cooler, electric fans wired to a switch used for towing only? The truck runs fine unless you put it under a load, my first thought is a bigger oil cooler, and trans cooler. could the intake gaskets be installed wrong? upside down blocking the water ports enough to raise the water temp under load?
Jon

 

Nice suggestions, but a transmission cooler was installed last year after the transmission was rebuilt. I had to replace the intake gaskets two years ago when I snapped a bolt for the thermostat housing. I know I have them aligned properly. The more I think about it, the more I am certain that the issue is some kind of minor break in the head gasket.

 

Put in a 180 stat!

 

You'll smoke a turd in hell for that one!

 

It's the smell of (typically but not always rich) exhaust, mixed with coolant. If you run an engine with this problem from cold start with the radiator cap off, and give a sniff right after the thermostat opens, you'll know the smell right away because it's so different from what you expected.

EDITED TO ADD: The sniff test is of the open top of the radiator, not the exhaust pipe.

While a small leak might be detectable with before and after compression test numbers, the change isn't necessarily great. A hairline fracture in the gasket might just hold the full pressure of a non-firing cylinder during a compression test, but vent into the cooling system when the cylinder is running live. Relying upon the compression test to find a known leak (detected in some other way) is kinda iffy because there are many different causes of varying cylinder pressures. A gross leak is always detectable with a compression test, but a small one and particularly a hairline fracture are not always so easily found that way.

Usually, a hairline head gasket fracture doesn't stay small for very long. There's a lot of heat and pressure on the cylinder side when the mixture ignites that tend to both burn and push the gasket open, then during the intake stroke the pressure reverses with greater than atmospheric pressure on the cooling system side and less than atmospheric pressure on the cylinder side. It's like bending a piece of metal back and forth to crack it.

 

One of the things that I've seen happen in the same hot running condition is a cylinder wall crack that is very small and, only when the motor is being pushed will it open up thus allow the coolant to enter into the combustion chamber thus be pushed out the exhaust site unseen and not noted by sense of smell.

In order to test for that, the motor must be up to full operating temperature. Then, ~ 15 psi of pressure is to be applied into the chamber with the radiator cap off.

NOTE: with the engine off, the piston may be blocking the path so, in order to thoroughly test it, the engine must be rotated / turned over slowly. If there's a leaker, you will note it via either bubbles in the radiator or, if it's bad enough, coolant geyser.

This may have been induced by the previous owner who failed to maintain a previous head gasket leak thus inducing thermal stresses into the walls of the combustion chamber thus inducing micro fractures thus a leak, thus the loss of pressure under full load conditions, thus the overheating issue.


CM

 

You couldn't ask for an easier test that that VW.