OT 91 Ford F700 Diesel Truck Engine

Tracy Brown · Jun 10, 2020

I just bought a 91 Ford F700 with a Ford inline 6 cyl diesel that has the oil and water swapping places. It is a 401 CI. I was told it has a blown head gasket. I'm thinking that is only a very hopeful guess. My first thought was a leaking seal ring on a cylinder sleeve. Is this a sleeved engine? If not, is cavitation a possibility like in some ford tractor engines? The tag on the valve cover says Engine Family LFM07.8EPC7. Thanks

agjim · Jun 10, 2020

It is not a sleeve engine. My first guess is cavitation. I have a L8000 with the same problem.

DRussell · Jun 11, 2020

Ford diesels are known for cavitation problems.

Determined · Jun 11, 2020

If you have oil in coolant and vice a versa it is a fairly unique situation so you need to focus on where the two can cross paths under pressure, places like an oil cooler if it has one.

Under pressure oil can get pushed into the cooling system then once the engine is shut down hot the coolant is now under pressure and can be forced back through the same leak into the oil system.

A cavitation leak can let coolant into the oil or compression into the cooling system but not likely oil into the coolant.

While I am not familiar with the engine you are working on a head gasket leak between a pressurized oil passage and a coolant passage does not sound very likely.

used red MN · Jun 11, 2020

I also have heard that those engines have troubles with cavitation of the cylinder bores. As Determined points out the oil cooler may be the best place to start diagnosing. If no joy there I would pull the injectors and pressurize the coiling system say 15 minutes then crack open the oil plug to see if coolant has pooled in the pan. Then crank it over and see if coolant comes out of any of the injector holes. Continue this probably up to three hours check every hour. If you have coolant in a cylinder maybe invest in a borescope for your phone, water proof ones are fairly cheap. The attached one is $17 and the camera is a little smaller than 5/16”, not pushing this brand or the seller it just an example that came up in a search. What I am saying is if you can get in there and see that it is leaking through a cylinder wall that could save you pulling the head of you decide to replace the engine. Going used in this case would be quite a gamble in my thinking.
Phone borescope

4play · Jun 11, 2020

I assume this engine has a oil cooler, if so I would check that too.

OT 91 Ford F700 Diesel Truck Engine

Tracy Brown

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agjim

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DRussell

Well-known Member

Determined

Well-known Member

used red MN

Well-known Member

4play

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