Cj5-head Gasket Or Cracked Block?

My '65 CJ5 has its original F134. Compression appears to me to be consistent and good (117, 119, 117, 121 PSI). The jeep fires up with no trouble whatsoever even in the cold.

But after it idles for a minute or two it starts puffing out white smoke. The cooling system also over pressurizes and starts spewing coolant after about four or five minutes. The radiator cap does not appear to be original but releases at its intended 13 PSI.

The white smoke will not stop at idle ever once it has begun on an engine cycle. But there is no white smoke at all when going down the road and the jeep is happy north of 40MPH in third gear.

What point(s) on the head gasket might I have a failure at? Is the fact that it gets worse once warm indicative of a block crack more so than a head gasket?

I have the knowledge and tools to pull the head but not a good place to work on the Jeep right now--getting too cold in Denver to tackle bigger project outdoors.

Thanks for any thoughts!

 

Most likely a crack in the block , usually between cyl #2 and #3.
I've had 2 like that with the exact symptoms .
I heard of others welding them up but I never did it.

 

When you say between the cylinders, where exactly do you mean? Like cracked between water jacket and the exhaust valves for those cylinders or do you mean something else? Thanks again for the help!

 

I concur. Crack is likely to run between exhaust valve seats.

I have had one such crack "stitched" sucessfully. The machine shop drilled and tapped several small studs along the crack, added valve seat inserts, then re-machined the deck surface.

 

While a cracked block between the 2-3 exhaust valves is high on the probability list, it could still be the head gasket. You are going to have to pull the head either scenario so may as well take a look.

 

X2, you need to pull the head to see if its the block, gasket, or head (unlikely).
-Donny

 

As mentioned, remove the cylinder head and inspect.

 

You all have convinced me! Off with the head--next weekend if the weather allows for it. Will report back on what I find--good to hear that some stitch repairs have been successfully made before if the cracked block does prove to be the issue. Thanks for the advice!

 

When pulling the head don't forget the single head bolt under the carb base.

 

I owe you all an update! Curiously enough the block was not cracked nor did the head gasket have any obvious failure points but obviously it was leaking somewhere. The cooling system, however, was totally clogged in certain passages inside the block. That was causing too much pressure to build up in the cooling system and I think was also forcing coolant improperly into the combustion chambers (presumably through the head gasket somewhere). I suspect the clog was due to the rig sitting for a lot of its life prior to my ownership. I'm sure the absolute best thing to do would be to pull the block and have it fully cleaned but I've cleared it well enough that it has no overheating or overpressurizing issues now. This is no show rig by any means but it is a blast to drive now that I have it running well! In the meantime, I've worked my way through various other rubber replacement and deferred maintenance!

 

Any "excess" pressure would vent through the radiator cap long before it breached a combustion chamber - UNLESS there was a leak in the head gasket already. "Clogged" water passages could not create enough pressure to blow the gasket.

The "pressure" and "spewing coolant" were signs of combustion chamber pressure leaking into the cooling system.

The "white smoke" is typically from coolant having entered the cylinder(s) after shut-down, through a damaged gasket, when normal residual pressure in the radiator is unopposed by combustion forces.

 

I had one with a crack in the cyl wall about 1/2 way down that caused these similar symptoms. A rebore and sleeve fixed it. Just saying.

 

x2

 

Yup new head gasket clearly was in order even though I didn't see the obvious point of failure in the old! I'm just celebrating a block that's good for now and doesn't have the typical crack!