ETHYL

The oil weight listed for the late model C4's is 5-30. As the mileage goes up beyond 75K, are you changing the weight to 10-30 or even 15-50. At this time, I have 94K and no oil is added between oil changes.

dbwade36

I have used Mobil 1 5-30 since I bought my 86 vette about 2 1/2 yrs ago. It does require adding about a quart between oil changes, but I do have 131k on this motor, (which is about the only thing I haven't replaced) hehe. I am looking forward to hearing some other responses to this question, as well. Want to make sure I am using the best viscosity for mine too.

greenvette95

5-30 Mobile 1 for my girl with 96,320 miles on her,.I Do not add between oil changes of 7,000 miles. LT1 auto.

Tvnewsengineer

First oil change after I bought mine in October, Mobil 1 15-50. Valve stem gaskets were causing smoke. Mechanic suggested this might help by thicking up the gaskets somewhat. Guess what, it worked. 153,000 on engine and now very little to no smoke out exaust.

Corvette Kid

I've had a recent change of thought on this. When I built my bottom end last year, I set the clearances a little looser than factory LT1 specs because I built it to run hard. That's fine and dandy and because of that, I thought I'd be better off with 15-50 M1. While doing some research on valvetrains while setting up my new heads recently, I found that in an engine with hydraulic lifters, heavier oils and/or too high of oil pressures can cause lifter pump up. While in a fairly stock engine this isn't likely to cause much more than a loss of performance, in a more modified one with valve to piston clearances close to the borderline, this could spell disaster! I'll be using 10-30 for warmer weather now and 5-30 in the winter. Also, viscosity has NO relation to film strength so with a top grade oil like M1 you're giving up nothing in protection.

comp

what is the coldest it get's there ???? 40 deg. and above you should be fine with 10-30 or 40

vader86

I was using 10w30 in summer and 5w30 in winter until this year, when I switched to 15w50 because I thought I had an oil pressure problem at idle. I will say this, it doesnt smoke quite as much on startup anymore (it was still just a puff before).

I'll probably go back to the 10w30 at my next oil change. I'm not sure yet.

Most mechanics will have a fit if you tell them you're running 5w or 10w30 in a car over 100K, I just politely nod and ignore them.

Jet-Jock

I've been using 5-30W Mobil for the last three years, but just switched to 10-30W for this last oil change to see if I notice anything difference. It doesn't get that cold in Florida so 5-30W is not as critical and the manual says 10-30W if its going to be 0 degrees or above. Since I change my oil by the seasons method (first day of each season), I'll probably run the 5-30W for the winter fill and go back to 10-30W for spring summer fall.

The weight type is dependent on your operating ambient temperatures.

Corvette Kid

For the next three months or so, it won't be unusual for morning start ups to occur in subfreezing temps. So as soon as It's dyno'd and hopefully run in an upcoming auto-X, I'll be swithing back to the 5-30 for a while for maximum protection on those cold mornings.

Yeah, like we old guys who are trying to expand our tech curve which began in the sixties!

runner140*

I have a 1996 with 86000 miles and still use Mobil 1 5W30. So far, no leaks and burns no oil.

redwing76

I've never heard of a interference problem with a chevy block. Well as you said stock that is.
You'd think that the push-rod would bend first.
With a big cam with a lot of lift it might be a problem, but only on a over-rev. But I will say this 15-50 is a bit over the top for a street car. Why not run 10-30 for a break in or even straight 30wt?

If you do a search on oil wieghts you'll see that there isn't much difference between 5-30 and 10-30.
Any multi grade is 20% plastic and 80% oil.

From everything that Iv'e read about oil Shell Rotella seems to be one of the better ones.

Southern Comfort

my 85 will turn 170K this month. I have found that Castrol GTX for high mileage cars in 10-40 works best for me.

I change it approx 2500 miles. Maybe burn .75 inbetween.

Mobile 1 caused my OP to drop to under twenty at hot idle. I stay up around 45 with the Castrol

Fuzzy Dice

Here in central Florida I use Mobil 1...10/30 all year...110,000 miles on the car...it's a street, strip car and no problems...I change oil every 3000 miles in deference to the track...