Discussion on oil weight

[reluctantartist]

Ok I do not want to get into a debate over oil brands or dyno verses synthetic oil. I want to discuss what actual weight of oil to use. A lot of posts discuss using lighter weight oils than specified in the owners manual. With the real hot weather that I am encountering (100+), I have been really wondering what people are actually running and what are the results. I have read in a blog about how vw industrial engine manuals state not to run in temperatures over 85.

The operating instructions for the industrial engines listed a range of air temperatures at which you could run with a maximum load on the engine. I think the upper limit was about 85 degrees Fahrenheit.

http://bobhooversblog.blogspot.com/2006 ... -temp.html In the 1985 vanagon manual it has the same oil weight guidelines as the 1982 aircooled manual: 20-50 (or other multi 50w oil) up to 85f and temperatures above that use 40w. If I knew I would be in temperatures above 70f all the time in the summer I would go ahead and run 40w like the manual says. But it seems unrealistic to switch to 40w for a few weeks and with weather where it gets below 70f and then peaks at 95+f what is one supposed to do? I found 25w60 oil exists and have thought maybe that would be more applicable if you are constantly encountering peak temperatures above 85f. I do not think running a thinner oil will run any cooler than a thicker oil in the summer, they should all flow through the oil cooler when hot and cool the same. Also if you run 200f oil temps at 70f at 90 it will be closer to 220f and less viscosity hence lower oil pressure. Plus I have a thermometer in my engine compartment and it is usually 10 degrees warmer in the engine compartment than ambient temperature. If you stop and then start it will be a lot warmer for a period of time causing oil temperatures to climb for a while. In the winter I run 0W30 since I deal with temperatures in the single digits sometimes.

[Hippie]

I'm just going to throw out a general fact that few people understand about motor oil and let it get ignored and buried in the inevitable same-old-discussion, but at least I'll put it out there. Generally speaking, you want an oil with the lowest grade numbers you can get away with, and the highest HTHS (high temperature, high sheer) viscosity number. The HTHS viscosity is the primary factor in wear protection that has any relation to viscosity. It is a good measure of the overall film strength of the oil at high temperatures. Some makers publish HTHSV, and some you have to email and ask. The reason they called for a straight 40 weight was that, at the time, it would offer the best protection in a hotter running air-cooled engine on hot days and high engine loads. The kinematic viscosity, e.g. 10W-40 determines flow rate, and you want good flow to keep things cool. The HTHS viscosity is how viscous the oil remains when being pounded by the bearings, etc. Motor oil, like ketchup thins out when under mechanical stress. (The opposite if Silly Putty that thickens and breaks when you yank it quickly.)

Oil pressure on your gauge tends to show the back pressure created by the oil pressing against the bearing gaps, and therefore tends to read higher with an oil with a higher HTHS viscosity and follows HTHS trends more than kinematic.

I like to see an HTHS viscosity of at least 4.0 cSt, and if the engine keeps at least 10 psi per 1000 RPM, you are probably about that HTHS unless the engine is worn. I used to Use 20W-50 in the summer, and 10W-40 the rest of the time, unless the engine was new and tight. (And 10W-40 in the Beetle because of the lower engine loading.)
With a sturdy oil like Brad Penn, Penn Grade 1, 10W-40 gave me sufficient oil pressure all year with its higher than average HTHS and also strong extreme pressure anti-wear additive package.

[reluctantartist]

The reason they called for a straight 40 weight was that, at the time, it would offer the best protection in a hotter running air-cooled engine on hot days and high engine loads

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I could agree with that argument except the later vanagons are water cooled and it still calls for 40w above 85f. Is your oil pressure the same with any oil weight and is the pressure the same whether the oil temp is 170f and 230f?

[Hippie]

Still, 1985 vintage motor oil. I'm not sure that straight 40 weight is overall better nowadays, due to its slower flow during the entire warmup period. But check the HTHS viscocity on the data sheet, if given, of SAE 40 weight vs. others. The HTHS is usually given at a standard temperature of 150 degrees C, at 10^6 sheers per second.

No, all oil pressure at the bearings varies with temperature, load, effective viscosity, filter/bypass setup, pump relief setting, and RPM.

Use whatever you like, but I usually used Castrol GTX conventional 10W-40 or 20W-50 with good results. Brad Penn, Pengrade 1 when I had it.

[DjEep]

20w50 year round here, with temps from 10F-105F. I personally roll Valvoline VR-1 Racing 20w50.

[Hippie]

VR-1 is good, tough oil, IMO.

[RSorak 71Westy]

I run 10W30 Rotella T as of lately, was running 10W40 synthetic Amsoil but it caused too much oil pressure (50 lbs, anything above 40 lbs at speed is too much) and ran hot because the oil cooler never got used. With the 10W30 it does and it runs cooler.

[dtrumbo]

Shell's Rotella T as well as Chevron's Delo 400 are formulated for diesel engines yet another friend of mine also swears by Rotella T in his VW's. How is oil for diesel engines different and why is it o.k. to run in our air cooled engines?

[RSorak 71Westy]

It's mainly for the flat tappet cam that our VW engines run, all modern motor oils do NOT have enough zinc to protect the flat tappet cams, as all modern motors have roller valve trains. The diesel oils have the required ZDDP.

[dtrumbo]

Got it! Thanks!

[vdubyah73]

i personaly know 2 guys that thought they were being slick. they took the remaining dregs that couldn't be pumped from 55 gallon drums of rotela and used it in their p/u trucks. they both lost a sgnificant amount of oil pressure after using it. this was good oil, didn't sit in an open drum getting contaminated. the pump was removed from an empty barrel and it was upended and drained into clean buckets. same shop two different times. first guy didn't work there anymore when second guy tried it. second guy was pissed no one warned him. i would have, had i known what he was up to. still wonder, was it the high zinc content ruined bearings, or pump or high detergent cleaned so well that true wear became apparent. both trucks were late 70's early 80's ford f250 4x4. the first guy did it just before i started there. second guy about 5 years later. i refuse to try it for this reason. castrol gtx, 20-50 summer 10-30 in winter.

any thoughts hippie?

[RSorak 71Westy]

I run Rottella in ALL my old cars, I have like 14 of them, and am a pro wrench, never had a oil related problem. This was just 2 guys with engines that were about to fail anyway.

[vdubyah73]

i've thought about that to, could be they were tired and almost done. these incedents didn't happen recently. over 20 years ago. trucks were only 10-12 years old.

[Amskeptic]

i've thought about that to, could be they were tired and almost done. these incedents didn't happen recently. over 20 years ago. trucks were only 10-12 years old.

Had a customer yesterday whose previous owner had a "crankcase flush".
Please . . . marketing gimmickry like that can destroy a Type 1 engine.

(his was a Type 4 with filter, but did ANYONE CATCH THE DRAIN PLATE FULL OF ALUMINUM SHARDS FROM THE PRIOR HELICOIL OF THE DRAIN PLUG????)

Just put some correct viscosity oil in the engine to the full mark and drive.
Sheesh,
Colin

[Hippie]

@vdubyah73: The dregs from a bulk drum are typically full of debris too small to see. I don't think the zinc/phosphorous settled out and caused an overdose to the bearings, as I have seen lab results on unshaken oil that was so old that it came in paper quart cans, and the numbers read the same as shaken oil from the same lot.

It can be so bad that Caterpiller recommends not pre-filling the oil filter when using bulk drum oil so that it all gets filtered the first time around.

...Just put some correct viscosity oil in the engine to the full mark and drive.
Sheesh,
Colin

That may be correct, but not very interesting.
Old fashoned zinc quantities (~1100-1200 ppm) are good for high pressure contact high lift cams, although it doesn't hurt to use a break-in additive for the first oil charge on a newly rebuilt engine, or possibly for aftermarket cams/lifters. I don't think the old VWs needed this much additive with proper parts. Just my opinions.
Always follow the builder's or manufacturer's recommendation.

cheers,
Rob