edac

I have a 99 1500 Express with 87000 miles, when I tow my 16 foot boat it will leak engine oil occasionally. Washed down the back of the engine, drove it around, and checked it, OK. Tow the boat, stop for gas and it leaves a puddle. Take off cowel and back on engine oil soaked again. Washed it off, added dye, drive it around and it won't leak. I'm kinda stumped. First time it was from Toledo Ohio to Chicago Ill., lost about 2 quarts.

Squigie

It sounds like you're overheating the engine (with a faulty temp sending unit), or running it in a near-overheat condition for too long. Overheating it can cause different parts to expand beyond their design limit, and cause leaks. -Due to different metals expanding and contracting at different rates.

It's also possible that you're overheating the transmission, and having some of that heat transfer to the rear of the block.

As an extreme example of dissimilar metals expanding at different rates:
I once had the pleasure of "executing" a Nissan Sentra. To do the job, I drained half of the oi, all of the coolant, pulled a few vacuum hoses to make it run lean, added a quart of 90% Isopropyl alcohol to the 5 gal of gas in the tank, and took it out on a 70 mph sprint on a 108 degree F day. When it lost power and forced me to pull over, the cylinder head was glowing red. After we let it cool down and towed it home, you could see where the aluminum cylinder head had expanded more than 1/4" in every direction, and scrubbed the sludge off the exposed portion of the head gasket. Yet, the cast iron block showed almost no indication of expanding at all on the same gaskets.

lunghd

This sounds familiar... several months back I towed my tractor into town on a stout car trailer & lost enough oil on a 10 mile trip to trip the oil light! No oil on engine, no smoking while towing... the oil was just "gone".

And so was my front rod journal & bearing.

RacerX

cant do anything until you know where the leak is coming from. stay tuned, with a light to track the dye.

edac

So, after driving around for a week, and occasionally checking with my uv light, I never found a leak. Drove from Chicago to Niagara Falls and back, added two Quarts. Now when I pull the cowl, I'm sure my clean engine will be covered in oil again.

Squigie

That makes it sound like it's a high-rpm issue.
It makes me wonder if your oil drain-back holes in the heads are clogged just enough to cause oil to pool when you have a lot of volume flowing. Then, it gets pushed through the valve guides, and sucked up by the PCV system. It all ends up going out the exhaust, and may not be noticed while on the road.

Are the plugs fouled at all?

edac

Thanks for the input everyone. Put a new PCV less then a month ago. This is not my daily driver, so it's not that urgent. But it seems like I might have to re-gasket the valve covers and intake. I'd much rather see where it's coming from.

edac

So I ended up doing an intake manifold gasket swap. Drove it for 700 miles. On the way back from fishing in Ohio 4/13, spun rod bearings 7&8. locked up motor 4 hours from home. Parked it in drive way. Just got finished putting in a long block. Now trans seems to be slipping. High RPMs in first, let off throttle to get it to shift into 2ond. Am still investigating trans issue. 2 hrs. and 5 miles on new motor.

When motor seized, popped hood smelled like burnt oil. Pulled dipstick,dry. Three months later oil level ok, dexcool looked new. I think tranny was failing causing high RPM's and spinning bearings. but why wouldn't the oil return to the pan?

My 84 was a pig on fuel but ran great for 250,000 miles. This one (99 express 106725 miles) is starting to get on my nerves.

lunghd

I'd quit while I was ahead... fix it, sell it (pull the tow bar so the next owner at least has a chance of driving it a while).

I'm saying that as a guy now running engine #3.5 . I'll never own another one of these GM junk-heaps again.

greenfire

Well.. towing with a 1500... just not the best truck for the job. Its a light duty van and just not up to the task. Next time get a 3500. It will have an oil and transmission cooler. And a transmission designed for towing.