Oil viscosity and CHT etc.... WOW!

[saggs]

I just rebuilt my 1.7 Cali motor over the winter in VT and upgraded to a 1911, different cam, rebuilt heads and 40mm Webers. I broke the engine in with Brad Penn 30w break in oil then added 20w50 after the first break in period. It's in an oval bug so not a lot of load to move around but my CHT was running over 375 at 70 mph with 75 degs OA temp. The oil light would come on steady after pulling off the highway at a stop light. I was bummed, thinking maybe I had done something wrong or had a main bearing issue? I searched this forum and found a thread by Pile talking about how much cooler his rig ran with 5w30 in the heat of Texas. I also saw talk about making sure the gasket on the oil pump cover was the super thin almost see thru one vs something thicker. Only having 25 miles on the motor, I got home from work today and drained the oil, changed the filter ( no metal in the drain pan..good) I pulled the pump cover and found that the gasket I used measured almost .011". The thread I read said it should be around .003-.004" I rummaged thru my gasket box and found one at .003"- installed that and added 3.5 qts of Rotella T6 5w-40. WOW! what a difference! I ran my beetle up a long grade going up to our hospital from a stop light and saw 70mph at the top (1/2 mile) and CHT was under 350 and oil pressure was up 10psi at a hot idle. The car pulled better and responded better, ran cooler etc.. I had no idea how much this would help but I'm glad it did as summers are short up here. Thanks to the STF again!

[twodollardoug]

I run 30wt amsoil z rod in my 2.0 in my 914. It's my dd and I live in the blistering hot desert of so cal.

[saggs]

is that a straight 30 weight?

[twodollardoug]

No. It's 10w-30. Group 4 synthetic.

[twodollardoug]

If they made a 20w I would try it. Flow is what we're after. With the protection of a true synthetic.

[saggs]

Do you worry about zinc content or is there enough in that brand?

[twodollardoug]

It is specially formulated for flat tappet cams. Now I sound like a damn amsoil salesman. I'm not. I'm not a brand loyalist. If there was a better oil, I would be using it.

[GARRICK.CLARK]

I use 20/50 in my turbo type 4 ,have done 4 a few years, think I'll swap it out for..... what grade would be best.
Will my motor be cooler also.

[saggs]

I know I saw a huge difference going from 20-50 down to 5-40. I think I'll go for a 5w-30 next, can't say much for the turbo oiling needs but I would suspect a good quality synthetic in a 10-30w would be fine?

[twodollardoug]

The higher the viscosity oil the more likely you are to be bypassing the oil cooler. Especially at higher rpm. I try to tailor my oil to my rpm. So at operating temp I like to see 10 psi per 1k rpm. I run 30wt in my type 1 early bus also.

[falcor]

Interesting, I'm running a 15w-50 now in my 914, might try a 10w-40 next time

[CLKWRK]

My approach to oil viscosity is whatever it takes to get 10 psi per 1000 rpm. So on a fresh rebuild i will start with 10w30 and go thicker if the oil pressure is too low and thinner if its too high
(Basically what Twodollardoug says)

[oprn]

Interesting stuff! I have never been a believer in the 50 wt oil trend. To me that oil is for 1/4 mile racers that purposely build their engines with large tolerances to avoid break in times and reduce friction. The only time I have gone as high as a 40 wt in the past is on worn out engines that are struggling to maintain any oil pressure at all.

My current 1911 is running on straight 30 wt HD diesel oil with zinc added and the oil temp is running a bit on the warm side. Not alarmingly so but getting out of my comfort zone so next change, in light of the info here I will look for some lighter oil.


Thanks all for the common sense posts! Merv

[twodollardoug]

What is your pressure at 4k rpm? Do you have a gauge?

[CLKWRK]

Viscosity directly affects the oil cooler bypass system ... thick oil pushes harder on the spring and opens the oil circuit that allows oil to bypass the oil cooler, this tricks it into thinking that the engine is cold even though it is warmed up or even too hot

Also oil flow moves heat away from the source, not pressure