Coolant in oil diagnosis

Hi all,

I was pushing my poor old truck too hard the other day, started to notice a lack of power on acceleration. About 20 min later engine started overheating. Dipstick shows about 3x the full level with oil and coolant. I'm assuming this is a head gasket, and am getting ready to tackle it, but wanted to check if I'm going in the right direction.

Thanks

What mileage and what engine?

I would check the intake manifold gaskets first.

250,000km, vin W

Head gasket..... Cracked head......BAD intake manifold gasket........ any of these could be the culprit.......Either way you have to tear her down to find the leak..... I would start with a compression gauge and go through each cylinder. If there all the same then it's the intake manifold.... This should at least give you a starting point..

The Chilton's manual is a little vague on a compression test; what's the correct method of turning the engine over with the gauge attached?

The Chilton's manual is a little vague on a compression test; what's the correct method of turning the engine over with the gauge attached?

Go through each cylinder one by one and see if you have a consistent reading with all six cylinders. If one is considerably lower than the rest that is your problem area. I believe your readings should be 100 or higher. If all your readings are the same then your problem is a bad intake gasket. To do this first unplug the coil wire so the motor won't start, Then take out 1 spark plug.... insert your compression tester and turn over your motor then record your reading. Do this for all six plugs...

You'll get a much more accurate reading if you remove all of the spark plugs, prop the throttle open, install the gauge and crank the engine over until you hear/feel 4 compression strokes. Do this for each cylinder and write down the results and label them as "dry". The test results should not vary more than 10% from the highest to lowest cylinder. Then squirt about a tablespoon of oil in each spark plug hole and check compression again on all cylinders labeling this test "wet". The wet results will be higher, but should not vary more than 10% from the highest to lowest cylinder. The wet test helps the rings seal and if the compression spikes higher on a particular cylinder, one or both compression rings are cracked/broken.

Thanks for steering me in the right direction guys. Did a dry compression test on the cold engine (forgot it should be warmed up) and all cylinders were between 177 and 187 psi.

So it looks like I'm dealing with a bad intake manifold, correct?

Also, is there any chance of damage from the oil/coolant mixture sitting in the engine if it's not running?

Compression pressures look good, however, passing or failing a compression test alone does not confirm the integrity of head or intake gaskets. A cooling system pressure test won't confirm anything you don't already know, (there's an internal coolant leak). Head gaskets leaking coolant into an oil passage is extremely rare on any engine. As MT mentioned, check the intake gaskets first. A visual inspection will most likely show a leak from a coolant port. The 4.3L has a very well known reputation of faulty OEM intake gaskets. If in fact yours are leaking, the Felpro part # MS98002T gasket set will solve the problem. Don't waste your time or money with any other gasket set, these are a proven permanent fix.

Coolant in the oil is only a problem if the engine is running. Make sure you change the oil and filter after repairing the coolant leak.