JHZR2
Staff member
Have some general questions regarding head gaskets. As some may know I have a few diesels which need HG work, and I’d like to take some of these on.
My 1991 350SD (call it car #1) is known to have HG and rod issues. Mine had oil in the coolant. Never did I find a situation where the cooling system retained pressure afterwards. It’s a pristine, low mileage example. I’m trying to get the HG done but my Indy had issues with the job and keeps getting a misfire at idle. It’s a side job so it’s slow.
I found another 91 (call it car #2) that has the same telltale oil in the coolant overflow. It cranks and starts beautifully when cold soaked in 30 degree weather. Overall car is very nice. It’s not as low mileage as my first one, but I can get it REALLY cheap. The difference with this one is that after sitting for some time (as ai understand it, days), the cooking system still had pressure. The first thing I did was open the radiator cap and it had pressure from who knows when. I started it and ran it (no boost, car was parked in), and no pressure or bubbles from the overflow.
Neither car had milkshake oil.
So:
Car #1 oil in coolant, no retained pressure in system.
Car #2 oil in coolant, sustained pressure many days.
I get it that it could be as simple as differences in the seal quality on the radiator cap (there is no overflow, the cap is on the bottle). But could one imply cracked head or some other issue over the other?
More general question - how could the system hold pressure and not push coolant back into the cylinder or exhaust? Every cooling system I’ve had stays pressurized for a bit as the engine cools down. But of course it goes away to nothing. This engine on car #2 was stone cold. I assume this means that the way exhaust gets into the system must only be under boost.
That question holds for my car #1. How is it
That oil gets into the coolant, but after the car shuts down, and oil pressure goes away, that water doesn’t make its way back in? I understand why it wouldn’t happen when the car is operating with >>16 psi of oil pressure.
I have a 1993 (W140 body style) with a perfect factory rebuild engine installed by Mercedes of Manhattan. The car is perfect on the inside except for the driver seat. Paint needs some help. But the engine and transmission are more or less perfect when running, and NO signs of an HG issue. This car may be a flip, or a beater, but I really bought it for the value of the hood engine and AT, being that they are the same model as my 91.
Of course my one 96 Ram also has the known overboard coolant leak from the HG. It’s very slight, I knew about it when I bought it, and didn’t make any issue driving across country. It was common. But it’s another project. Thus I’m interested in learning about head gaskets. If I can know how to deal with this, I think I can make a variety of nice diesels and other nice cars come back to life as a hobby. I have the tools and space. Just not the first go at it and a few learning points along the way.
Anyway, any insight would be appreciated.
Thanks!!
My 1991 350SD (call it car #1) is known to have HG and rod issues. Mine had oil in the coolant. Never did I find a situation where the cooling system retained pressure afterwards. It’s a pristine, low mileage example. I’m trying to get the HG done but my Indy had issues with the job and keeps getting a misfire at idle. It’s a side job so it’s slow.
I found another 91 (call it car #2) that has the same telltale oil in the coolant overflow. It cranks and starts beautifully when cold soaked in 30 degree weather. Overall car is very nice. It’s not as low mileage as my first one, but I can get it REALLY cheap. The difference with this one is that after sitting for some time (as ai understand it, days), the cooking system still had pressure. The first thing I did was open the radiator cap and it had pressure from who knows when. I started it and ran it (no boost, car was parked in), and no pressure or bubbles from the overflow.
Neither car had milkshake oil.
So:
Car #1 oil in coolant, no retained pressure in system.
Car #2 oil in coolant, sustained pressure many days.
I get it that it could be as simple as differences in the seal quality on the radiator cap (there is no overflow, the cap is on the bottle). But could one imply cracked head or some other issue over the other?
More general question - how could the system hold pressure and not push coolant back into the cylinder or exhaust? Every cooling system I’ve had stays pressurized for a bit as the engine cools down. But of course it goes away to nothing. This engine on car #2 was stone cold. I assume this means that the way exhaust gets into the system must only be under boost.
That question holds for my car #1. How is it
That oil gets into the coolant, but after the car shuts down, and oil pressure goes away, that water doesn’t make its way back in? I understand why it wouldn’t happen when the car is operating with >>16 psi of oil pressure.
I have a 1993 (W140 body style) with a perfect factory rebuild engine installed by Mercedes of Manhattan. The car is perfect on the inside except for the driver seat. Paint needs some help. But the engine and transmission are more or less perfect when running, and NO signs of an HG issue. This car may be a flip, or a beater, but I really bought it for the value of the hood engine and AT, being that they are the same model as my 91.
Of course my one 96 Ram also has the known overboard coolant leak from the HG. It’s very slight, I knew about it when I bought it, and didn’t make any issue driving across country. It was common. But it’s another project. Thus I’m interested in learning about head gaskets. If I can know how to deal with this, I think I can make a variety of nice diesels and other nice cars come back to life as a hobby. I have the tools and space. Just not the first go at it and a few learning points along the way.
Anyway, any insight would be appreciated.
Thanks!!