Mixing Oil Grades?

[NV Zeno]

'83 EA81, 319,000 miles:

 

I've been using 10W-40 in this car for the last 220K or so, and have had absolutely no engine problems (oil related) the whole time.

 

This past winter, right at startup I heard a very brief (perhaps 0.5~1 second) of what sounds like oil starvation and a couple of light knocks. This happened when the temp in the garage is below about 25F, and only after sitting all night.

 

Lately the temp's been warmer than that, around 30F at startup time in the morning, the sounds don't happen anymore.

 

I guess this is kind of a roundabout way of asking what your opinions are about mixing some 10W-30 or even 5W-30 with my usual 10W-40, maybe just in the wintertime. I'd rather not go to the thinner oil 100%, as I run some high RPM on a long uphill grade often. I'm also considering there must be at least some slop due to 300,000 miles of use, so I figure the 10W40 is good for a general purpose oil.

 

Thoughts?

[nipper]

ON non synthetics, studies have shown after a few thousand miles almost all oil ends up as 30 weight. If you mix 10w30 and 5w30 evenly you will get 7.5w30 (same for the other numbers).

 

You arent going to hurt anything by mixing oil weights. i would however recomend staying within the same brand, or at leats type. Every oil compnay has its own special cocktail of additives. Again your not going to hurt anything, but why risk it.

 

nipper

 

PS check the oil pump to make sure its in spec, it may be on the high end of tolerances and need rebuilding.

[GeneralDisorder]

Definately check the oil pump - frankly if it hasn't been replaced I would just get a new one on general principle. The one from my Hatch looked pretty bad at 224k but the engine is strong and I just replaced the pan + gasket and it had no metal other than the usual amount of ultra-fine shiny flecks. The pump sees pre-filter oil from the pan and the sleeve bearings inside them are aluminium. They usually are REALLY ugly inside after 200k+. If I have my way they get replaced at 100k intervals.

 

As far as oil grade is concerned - why are you running 40 weight? These engines really should be run with 30 weight under most circumstances. The tollerances are very close - they don't get much larger under normal conditions. Usually when the tollerances reach a point where a thicker grade is needed the bearings are about shot and going to a heavier oil isn't going to help.

 

GD

[3eyedwagon]

'83 EA81, 319,000 miles:

 

I've been using 10W-40 in this car for the last 220K or so, and have had absolutely no engine problems (oil related) the whole time.

 

I'd rather not go to the thinner oil 100%, as I run some high RPM on a long uphill grade often.

 

 

I would guess that's why he is using 10w-40.

 

I usually bump oil viscosity up in the summer time, in preparation for trips through mountain passes in higher temperatures than normal.

 

I've never found any real problems with running a slightly higher viscosity than usual. Especially if it is a multi-viscosity oil. Then again, everything I do this to is high mileage, and usually a v8. So, chances are; I'm not going to hurt it.