Hi,
When I read the question I knew what to say, but w41quad4 beat me to it.

There is a real danger of starving the crank and main bearings for oil when going to higher viscosity than the engine was built for.
Just to make my point, imagine the sump filled with chassis grease.
The pressure would literaly blow the filter open once the pump got hold of the grease.
Would the flow of lubricant to the bearings be sufficient? NO!

Remember that the oil flowing through the bearings have two main functions:
1, Lubricate the bearing, preventing metal to metal contact.
2. Cool the bearing, there is a lot of head generated in a crank or main bearing.
(I have stripped an engine where there was burnt oil (coked oil?) stuck to the main bearing caps. The same smell as a fried auto trans.)

Stick to a synthetic oil, with the factory/engine builders recomended weight.

Br//

 

Personally, I think as long as the 20w-50 oil is synthetic, you won't notice too much difference. 20w-50 is for racing motors and high performance street vehicles. I run the Amsoil 20w-50 racing oil in my motor. The stuff pours like 10w-30 dino oil. I tow a lot and regularly spin well over 6k rpms. I want the extra protection. I watch the oil pressure and once it is up to temp, the pressure is not much different than when I had 10w-30 synthetic in there (3-5psi on my scanner). In the winter time I'll watch the oil pressure and if it is way up there from what it is now, then it tells me it is too thick and I'll change it.

In Texas heat, which is damn near that of AZ, I'm not sure if you'd ever have to worry about it thickening up too much. This is all IMHO.

 

Does anyone run thin oil like 5W20?

 

there is no reason to in a stock truck..i use valvoline 20/50 in my dirt track car but thats a high rpm motor that always running from 5500-7500 rpm constantly

 

What does the pressure do when you go WOT? 45psi cruising is plenty of pressure and i wouldn't worry about 30 at idle either. My biggest worry would be that the pressure builds sufficiently when you stomp the pedal.

 

I was thinking of using the 5W20 at the track to see if it made a difference.

 

well I have not changed the oil yet as far as switching but when the motor is at full temp and idle it is at 20-25 now. It does go up under full throtle but my only concern I think the guy he put in my cam bearings messed up in one way or the other. I will be going to a slightly thicker oil on this comming change.

 

Royal Purple 10W40 here this stuff is awesome! Love the RP 10W40.

 

that is what I was thinking of trying first. I let you guys know how it goes

 

Really you only need about 10 psi per 1000 rpm up to about 45psi. I work on 1000hp pump gas chevrolet engines in boss hoss motorcycles for a living and i have talked to our engine builder about this quite extensively, the thinner the oil the better it flows and moves about the engine and also cools better. In that motor i would only run 10-30 maybe 10-40 in summer heat. If you talk to a builder they will tell you pressure isnt as critical as volume and are not necessarily correlated with each other, and the thinner oil will have better flow=more volume. Just sharing my knowledge on the subject.