Mechanics

LOW COMPRESSION QUESTIONS

1993 Nissan 240SX

Engine Performance problem
1993 Nissan 240SX 4 cyl Two Wheel Drive Automatic 168000 miles

Hello, I own a 1993 Nissan 240SX w/168,000 original miles. I purchased the car new and know that the car/engine have not been abused.

I've noted (for a few years now) that the cylinder 2 spark has oil - not only on the pug tip area, but also on the base of the plug. The other 3 plugs look good.

I ran a compression test (following Nissan manual guidance) and came up with very low results:

Cylinder - PSI - PSI after adding a little oil
1 - 110 - 135
2 - 105 - 130
3 - 105 - 115
4 - 110 - 130

The Nissan (1993) manual says that PSI should be 179, minimum - 151, and max difference between cylinders - 14.

The car runs fine - no stumbling, missing, etc. It burns/loses virtually no oil. Performance may be down somewhat - but it is not significant. (I drive the car mostly in town, drive the speed limit, no jack-rabbit starts, etc, and as the car has aged - so have I - not " Speed Racer" or the like.)

My questions are:

1. How concerned should I be about the abnormally low compression?

(My goal is to continue to own/drive the car sensibly - without experiencing serious mechanical issues.)

2. If the cylinders continue to lose compression (over the next several months/years) - what symptoms/issues will I most likely experience with the car?

3. Outside of pulling apart/rebuilding the engine/head - are their any additives/products you would recommend I look into to help restore (some) lost compression?

I've seen various products at the auto store advertising their ability to restore lost compression, etc, though I confess to being a skeptic.

Thank you,
Mark McKamey
Mark. McKamey@us. Army. Mil
Avatar
Mrmisman17
May 8, 2008.



The oil on your plug. You might have a leaking valve cover gasket around the spark plug hole. Check, if there is, then change valve cover gasket set. Your compressions are a bit low, if you did it right. Try added the engine restorer additive from your local auto parts store. It may help increase your compression and fix some of the cylinder pressure leakage from weak rings.

Tiny
Tee22
Jul 26, 2008.