Oil Grades and Temps advice?

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Oil Grades and Temps advice?

Post by Richierich » Tue Jul 11, 2017 8:27 pm

I have a new pro-built 2276 - new aluminum case, doghouse cooler, 26mm oil pump, full flow with external filter. The motor is in a street Oval with decklid standoffs (top) - all tinwear in place, stock sized bottom pulley.

The oil subject has me really confused and unsure what to do for a couple of reasons.

Having got the engine in the car (builder did the cam break in etc) I was told to use 20w50 mineral oil (I'm in the UK and fully synthetic 10w30 is NOT available here) which I have. New filter on etc and took the car out for 10 or 15 test miles and then to seat the rings etc. Oil pressures all good during the 15 or 20 miles but when I got back to the shop the dipstick was pretty damn hot - I shot the case with infra red gun and I was getting between 235-260f - depending on area - and this was after the motor had been switched off for maybe 5 minutes. The weather that day was sunny and maybe 75f. I am not at all questioning what the builder told me - he's done a superb job of the engine - but a lot of the info I read seems to indicate that using a fully synthetic 10w30 will drop oil temps 15-20f? Is this correct and if a 10w30 is not available, what other grades could I use?

Could the slightly elevated temps be due to new pistons, barrels, aluminium case etc - all other things being equal?

Thanks for any advice or guidance in advance.

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Re: Oil Grades and Temps advice?

Post by ps2375 » Tue Jul 11, 2017 9:11 pm

Richierich wrote:
Tue Jul 11, 2017 8:27 pm
Could the slightly elevated temps be due to new pistons, barrels, aluminium case etc - all other things being equal?
Almost definitely. Don't forget bearings too. They all need to "run in" to get happy.

I can tell you that my motor ran cooler after going to a thinner oil after I read up on things. My motor was built decades ago and when my father (previous owner and the builder) was driving it, he sometimes had higher oil temps with it, even after adding a sump and going full synth, but staying with the 20/50 weight oil. After life got in the way and he parked it for 20 yrs, I got it. I went thru the motor, had to replace a cylinder, the ONLY thing I changed other than that cylinder were the rings and went with a 10/30 syth oil. I never had any issues with oil temps, and when I told him that and the theory behind it (thick oil bypassing cooler, causing hotter oil, but not thinning enough to not bypass cooler) he was surprised.

I'd find out what the actual oil temps are and go from there. Personally, I'd install an oil temp gauge somewhere(even if it were temporary), then go to a thinner oil and break in the motor fully and see what the temps do. No new motor should need 20/50 oil in it. Unless he built "loose". You'll have to see what the temps and pressures do with a thinner oil.

If a 10/30 isn't avail, I'd have no problems with a 5/30, at least in my motor. Your pressure gauge will tell you what it needs and I bet the temps gauge will back it up.

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Re: Oil Grades and Temps advice?

Post by Slow 1200 » Wed Jul 12, 2017 7:35 am

I would ask your builder first....if he used loose tolerances (some builders do) thiner oil might not be such a good idea

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Re: Oil Grades and Temps advice?

Post by FJCamper » Wed Jul 12, 2017 9:18 am

The Type 1 VW engine case from the first Strength Through Joy show cars and Afrika Corps kubelwagens was designed for 30w oil. The Porsche theory of oiling (high volume, low pressure) was directly opposite to most water-cooled engines, which can have two or three times the hot idle pressure of a VW. This is why the factory never put oil pressure gauges in Porsche street sports cars. The low readings would have scared the customers if they compared it to n MG.

As the Type 1 engine was enlarged over the years, the oil pump size and oil pressure relief valve springs rates were increased to improve oil cooling.

But the whole scheme was still based on 30w oil with the caveat that VW finally allowed multigrade 10w30 oil as the 1600's replaced the 1500 engines.

Oil pressure is resistance to flow, so an increase in oil pressure is not, in and of itself, an improvement. That's why 20w50 or similar heavy weight oils don't help except in very worn engines. And because we don't have oil volume gauges, we rely instead on oil temp readings.

A 10w40 or 20w40 multigrade is about max for a Type 1 engine so that high viscosity doesn't fool the oil pressure relief valve.

Being racers, we are aware that thin oil produces the highest HP. However, 0w5 or 5w20 oil, so common in most street cars these days, is designed to function in modern engines with very small oil galleries and tight clearances. That how they keep the pressure up.


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Re: Oil Grades and Temps advice?

Post by Marc » Thu Jul 13, 2017 2:21 am

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