This is definitely not for lt1tech IMO but, why does GM not recommend 10W-40 in our LT1 motors? I just started using it the first time and my oil pressure has never been better? @idle it used to be a pubhair above 20psi at normal op, now it is around 30psi and regular load driving @1500RPM's it is still a little above 40psi. What gives?

 

Thicker oil kills HP.

Daren

 

You only need 10psi per 1000rpm to lubricate the engine. You are wasting energy by pumping thicker oil at a higher pressure. The engine is designed to survive with the cooling and film thicknesses provided by the viscosity of a 30-weight oil.

 

I just did not understand it since my 67 327 I ran 20 50 thru it and never had a problem, I know about pressure formulas and horsepower loss I was just curious why they say not recommended...I willl be changing it out to 10-30 this friday but GM never gives a thorough explanation.

 

Thicker oil also cuts fuel economy. With high mileage emission and lifetime fuel economy targets, OEMs design for lower viscosity oils. They especially like synthetics, like M1 factory fill on Vette.

 

GM designs clearances tighter these days in comparison to the early small block engines. Thick oils are suitable for big bearing clearances but may not flow properly in engines with tight clearances.... especially when cold. Some safety has to be built in for the moron that holds it to the floor 30 seconds after a cold start-up. Aluminum motors may also have tighter main bearing clearance when cold to compensate for the greater expansion that aluminum has over steel.

As stated in previous posts, thin oil gives better mileage & HP... a big deal when federally mandated fuel economy standards can cost auto manufacturers penalties when cars produced are below a certain limit.

Will 10w40 work? Yes it will & also may help reduce the oil consumption problems that some LS1 motors exhibit. I have 2 examples (5.3 Chevy trucks) locally where this helped. Also a customers stock bottom end '99SS is running low 10's at 7000rpm on 10w40. Would it blow up or go faster on 5w30.... not sure if either would happen but I hate to mess with what works.

Do I recommend it to anyone reading? No, mainly because I do not want to be responsible for your engine, but I would do it on mine after it racked up some miles.

Just something to think about.

 

Here's my special mix

4 quarts of Vavaline synthetic 5W-30
and i quart of lucas oil. Oil pressure runs perfect, and helps reduce blowby since the rings and everything is worn.

 

Confucious say "oil is oil" Just depends on how much you want your pump to have to work

 

You put that glorified gear oil in your engine?

The only thing that stuff does is cause the oil to foam in certian situations due to the fact it doesnt contain the anti-foaming additives that normal oil contains.

Whatever floats your boat I guess.

 

Please explain what you mean by "Oil pressure runs perfect"

 

As far as fuel economy, I haven't changed my driving habits and I filled my tank on monday and today I have 1/2 a tank and my mileage says 250 so fuel economy is not affected.

 

I usually do five quarts of mobil 1 10w30. Last time I did four quarts of 10w30, and one quart of 15w50. I get better pressure than I did before. However I do still have some spikes in oil pressure under heavy acceleration, but no one seems to be able to figure it out.

 

Hey John.....go figure.....thats the same mixture I was planning on running in my motor.

 

It seems to work really well. From what I have read Mobil 1 is a little on the light side for a given weight. IE there is a range that you can be within and still classify the oil as 10w30, and mobil 1 is on the light side of that range. I got a lot of good info off of www.bobistheoilguy.com

Great forum, and great group of guys over there.

John

 

My car actually runs better and quicker with the 5W50 castrol syntec.