Excessive Oil Consumption

[donmattson]

I own a 1995 C1500 Chev WT with a 4.3 engine. It has 254K miles and I drove 93K in 2007 escorting oversize loads. Other than high miles, the engine runs well.

 

For about six months, I was losing coolant at the rate of a gallon every month or so. Two weeks ago, I had a mechanic perform a pressure test. He recommended replacing the intake manifold gasket. The gasket replacement fixed my coolant leak but I used about 3.5 quarts of oil in the last 500 miles!

 

I returned the truck to the mechanic. He could not find visible leaks on the bottom of the engine. He put dye into the oil but the tailpipe showed clean of the dye.

 

Spark plugs were new about 5K miles ago; wires are about 10K old. Engine idles well and begins to almost to misfire at 55-60 mph. The computer, I assume, keeps the engine running well.

 

The mechanic said the surface of the intake manifold was smooth and clean when he reinstalled it. He could not see or feel any heat damage. He replaced two other gaskets this past week with no problems such as mine.

 

Other than piston rings going south on me in the time after intake manifold gasket replacement, I cannot come up with anything else that would cause such high usage.

[markw8]

All that antifreeze might have caused cylinder scuffing. But that much should show on the plugs if its burning it. Make sure it's not getting in the coolant. Mark.

[donmattson]

Since posting this situation, I drove about 3000 miles. I have added about a quart per thousand miles. The mechanic changed the oil and used 20W/50; I have been using 5W/30 and the garage thought it was too thin. The major change I see is a bit higher oil pressure. However, the oil seems like I am pouring honey or molasses! Oil consumption decreased from a quart per hundred miles when I first posted. I assume the mechanic and garage is trying to "seat" the intake manifold gasket.

 

Gas mileage remains average and performance is good. I don't see clouds of black smoke out of the exhaust. No oil is on my garage floor.

[Mikeee]

Yep, I'd say the running 5W/30 is waaaaaay to thin for 254,000+ miles.

 

I have 345,000 on my 4.3 and I add a quart of 20W/50 every 180 miles. I don't need to do "oil changes" anymore.

 

Add oil ... check the gas

[cammiller]

I have had a set of intake gaskets go south and burn oil. You could not tell by looking at the tail pipe and it did misfire. The plug for the hole that was misfiring had an excessive build up on it. Turns out that portion of the intake gasket was leaking internal to the engine on the runner. I sprayed a little brake cleaner into the crankcase and the engine stumbled.

[donmattson]

You wrote that a "portion of the intake gasket was leaking internal to the engine" – did that mean a portion of the gasket failed over that cylinder or that it shifted when the intake manifold was reinstalled? Did you install a new gasket? Have you fixed the problem?