Motor is hydrolocking.

[Sycostang67]

My sister has a 1991 F-250 4x4, 7.3 ATS 085 with a 5spd with at least 143k miles. About two weeks ago she said it started fine but smoked white a lot, and continued to smoke the whole 10 minute drive to the tire shop. It was pulled in right away and only sat long enough to rotate the tires. When they went to start it up, it was hydrolocked. Her husband came home last week, he went out and it fired right up but was still smoking really bad. He parked it in front of their garage, shut it down and let it sit for 20 minutes at which point it was hydrolocked again. There is no sign of coolant in the oil, but the coolant level was too low to check the first time it locked up. He just had the injectors tested in case one was leaking really bad and they all passed. He just rented a cooling system pressure tester. Does this sound more like a head gasket issue or a cavitation issue? The truck had been running fine and smoke free up until the day it first locked up. My sister said the temp never got hot either. I will repost with the pressure results when I get them.

 

[riotwarrior]

to me HG as it's showing constant flow of coolant with white smoke....

Engine stops in about 2 - 3 spots only and if piston covers the porosity caused by cavitation it won't hydro but if it stops below the porosity then it will bleed coolant.

The same for HG if piston at TDC won't likely fill to much but if lower it can fill and hydrolock...

fifty fifty to determine, and in all likelyhood based on the info you provided, I'm guessing HG, but pulling heads is really only way to tell that I know of

 

[Bashby]

You could pull the glow plugs, pressurize the coling system and see if coolant comes out of one. If it does rotate the engine until that cylinder is at TDC. If coolant flow stops it is cavitation. Of course if the cavitated cylinder is already at TDC when you test you won't see coolant from the glow plug hole. Rotating the engine by hand 90 degrees or so a few times should show a leak.

 

[icanfixall]

Whats posted above is mostly correct. What I can add is just remove the glow plugs and crank the engine over. Watch the open plug holes for a gusher of coolant. Might be one cylinder or 2 side by side. Thats still not going to be a sure way to know head gasket or cavitation so pulling heads is the next step. Also please don't pull just one head. If you do its possible you will be doing this same job again on the other side seeing that one head gasket let go usually the other is not far behind that one. Also might want to have the heads checked for valve guides and cracks.

 

[chris142]

its my beliefe that a hg wont normally fill a cylinder.some white smoke maybe.a hole in a cylinder will fill it up fast though.thats my thoughts anyway

 

[lindstromjd]

its my beliefe that a hg wont normally fill a cylinder.some white smoke maybe.a hole in a cylinder will fill it up fast though.thats my thoughts anyway

Depends on how the HG blows. My '84 that I gave to my little brother blew a HG and it was pouring water out the back of the block almost as fast as a garden hose would fill the system up.

 

[Sycostang67]

He used the pressure tester, pumped up to 15psi and it dropped to zero in less than 30 seconds. He will be pulling the heads next week to have a look. When he pulled out the injectors, he said 4 and 6 were covered with slime. Is it possible the gasket blew between those two cylinders?

 

[tbiagent69]

From my experience I'd say almost 100% that it's a head gasket, but I've not dealt with cavitation before.

Cavitation / cracked head would most likely only affect a single cylinder.

 

[tbiagent69]

And +1 doing both gaskets at the same time.

 

[Sycostang67]

He will be doing both of them, he agreed there was no point going that far in just to do one.

 

[icanfixall]

With 2 cylinders that are next to each other like you have posted I will say its positively a head gasket blown between those two cylinders.

 

[riotwarrior]

I'd bet it's a blown gasket between cylinders too based on what you said

 

[Sycostang67]

I have an update to this issue. The heads were removed, he was unable to determine exactly if or where a head gasket may have blown. I only glanced in to see that the cylinder #8 was rusty from coolant. He took the heads in to have them checked, found cracks in the valve seats and guides were shot so they were completely rebuilt. He is putting it back together this weekend...hopefully.

 

[icanfixall]

Thanks for the update. Hope it runs and no more problems are found with coolant.

 

[Sycostang67]

Well he finally got the truck put back together...pretty sure his block cavitated. It acted like it was hydrolocked when he tried to start it, pulled the #8 injector and coolant came spraying out. He is using my spare 7.3 while he gets his motor rebuilt and sleeved over the winter.