1987 Thomas Bus with a blown up Cat 3208 - what do?

[jcalvinmarks]

We've had a bad week with our bus (1987 Thomas Chartour). After our last short trip, I discovered that some coolant had been pushed out through the overflow, and then discovered coolant contamination in the oil, after which point I drained about a gallon of coolant out of the oil pan. Long story short, I'm pretty confident we have a crack in the block, so this bus is going to need a new engine.

So the question is, what are we going to do about it? I figure we have three basic options:

- Swap another Cat 3208 from a Thomas bus. I would assume this will require the least amount of fiddling since the engine will already be configured for rear-engine application in a bus from the same manufacturer. But the very newest buses with a 3208 are no less than 20 years old now, and are likely to be several years out of fleet/revenue service. So mileage and condition are going to be a big question mark.

-Swap another Cat 3208 from a fire truck, probably a Ford C8000 or similar. Fire truck engines are likely to have very low miles and are generally like to be well-maintained. But I have to imagine that it's going to require a little bit of engineering to convert from a cab-over truck to a rear-engine bus.

-Swap for something else entirely. I had a mechanic recommend a Cummins 4BT, but going from a 235hp 10.4L V8 (which even at that feels under-powered at times) to a 4-cylinder 3.9L that makes only just 100 hp doesn't seem like a good fit. What other engines should I be considering. It would need to be all-mechanical, since there's no wiring harness for anything with an ECM, and mate up to an Allison MT643 transmission.

[Ronnie]

I would dig into your engine a bit more. Could be an oil cooler, or maybe a head gasket. A cracked block would be kind of rare. Cracked head maybe, and that would not be to hard to replace. Dropping the pan and pull a(or two) rod bearing to see if it is wiped or ok would also give you an idea if the engine is really shot or not. While the pan is off you should be able to see the cylinders, at least the lower part, any cross hatching still there, scoring, rust? A pressure test with the pan off would show any individual cylinders leaking from a head gasket or head crack.



Just my thoughts.

[jcalvinmarks]

We actually *just* had the pan off in November to do the main bearings, the cylinders looked good (or at least as much of them as we could see). We could still see cross-hatching, at any rate. It has only 160k miles and about 5k hours on it, so the engine itself shouldn't be wiped out just on account of wear.

But the volume of coolant in the oil makes me worry that there's a problem internal to the engine. I would think a blown head gasket wouldn't be sending this much coolant into the crankcase. If it's being exposed to combustion, the coolant would be vaporized and exhausted out, right? With maybe a smaller volume of coolant contamination for whatever of the steam is able to make it past the piston rings? Or am I not thinking about that right? It's also running smoothly, no misfiring.

I guess I'm preparing for the worst. I'd love to hear that it's just head gaskets. Although I'd hate to spend the money to have the heads removed only to find out that it was a cracked block after all.

[joeblack5]

When you shut it off while hot you have pressure in your coolant system. No oil or combustion pressure anymore.so where it can leak it will. If you do not have oil in your coolant then maybe head gasket.
Anyhow as Ronnie said.. some work to check but a lot less work then exchanging an engine..

[Ronnie]

I would still get a pressure tester to pressurize the coolant, and see where it is leaking. A head gasket can leak into the oil, or leak into the cylinder and drain into the oil while the engine is off.


The oil cooler I would for sure take a good look at. Real common failure point. Normally you will get oil in the antifreeze if the oil cooler leaks, so if the antifreeze is real clean and antifreeze is in the oil but not the other way around then not to likely to be the oil cooler.