99 Engine problems

[geoffmalter]

Bought a used 99 Miata and discovered several months later that it was burning oil at a rate of approximately one quart every three weeks.

My local dealer did a compression test and said two cylinders had low compression. Their conclusion: bad rings and the engine should be replaced, or we should continue to top off the oil. The car is driven approximately 10,000 miles a year.

Two local independents say that the milage is too low (56,000) for it to be rings. They think it has to be something else.

Has anyone run into this problem? Your experiences, please.

 

[kcbhiw]

I have a '99 engine with bad rings on the #4 cylinder (~15% leakdown). However, it has about 120K miles on it.

Did the dealer give to you, in writing, what the actual compression results were? Take it to a shop that has the ability to perform a leakdown test. That'll defiantely indicate whether you have bad rings or bad valve seals/guides.

 

[geoffmalter]

Thanks for responding.

The dealer ran two compression tests. A "dry" (normal test) and a "wet" (where they place oil on top of the pistons). Results:

Dry test: #1-175 #2-150 #3-120 #4-155

Wet test: #1-175 #2-150 #3-130 #4-170

The car runs fine, never smokes or misfires, and last month it passed the Calif "smog" test for vehicle registration with flying colors.

The only noticable problem is burning of oil at the approximate rate of a quart every three weeks. Currently using Mobile synthetic 10-30 wt.

 

[aMaff]

that number 3 seems a little low for an engine w/ that few miles on it...

 

[kcbhiw]

that number 3 seems a little low for an engine w/ that few miles on it...

I agree.


Geoff, It's possible the the engine inhaled something at some time to score the cylinder wall. At this point, I don't think there is much you can do short of bottom end rebuild . I'm in the same boat as you.

 

[geoffmalter]

For the layman, what does a bottom end rebuild consist of? Thanks.

What could the engine have possibly inhaled to score the cylinder walls?

 

[kcbhiw]

For the layman, what does a bottom end rebuild consist of? Thanks.

Rebuilding of the cylinder block. Basically just an overbore or hone may be all that it needs, but the pistons and rods will need removal which means the engine will need to be removed from the car.

What could the engine have possibly inhaled to score the cylinder walls?

I haven't a clue. How dirty is the air filter?

 

[geoffmalter]

I looked at it yesterday after reading the posts. The air filter has been in for nearly a year; still fairly clean (at least to this layman).

 

[kcbhiw]

Unless passing emissions becomes troublesome or drivability is affected, I say just keep an eye on the oil level and drive on .

 

[geoffmalter]

Thanks for everyone's support and comments.