Old cars, synthetic oil

[AK260]

The debate rages on but this I feel is a good bit of food for thought .....

 

 

 

What are your views?

[siteunseen]

I ran Kendall GT-1 in an old 911 I had. My mechanic swore by that stuff for air cooled motors. He said prop planes used it too. I think it was synthetic or a synthetic blend. I know it was $10 a quart in the '90s and for a 13 quart oil change that was one more reason I went back to Datsun Zs. 

I've always heard you can go from dino oil to synthetic but once you use synthetic you can't go back to dinosaur fossils???

[grannyknot]

This forum is probably one of the few where you could have an oil discussion without it ending up as a flame war. 

I thought the "synthetic vs dinosaur oil in old engines" debate had been resolved years ago.  There are some guys who used the first formulations of synthetic oils and had there engines leak still claiming that it's bad for old engines but I think the general consensus of car guys agree that was only the case with the first synthetic oils.  At least that seems to be the case in the forums on bobistheoilguy. I've been a lurker on that site for a few years and it's quite something to see the sheer volume that has been written about oil.

[240260280]

Perhaps the comparable key points can be limited to  lubrication/wear, deposits, replacement interval, seal interaction, and costs.

[AK260]

What I’ve learned from all I’ve read, in what I hope is a succinct way is that:

 

1. ZDDP - is important in the correct amount as it creates a “sacrificial” layer for our non-roller cams and reduces wear on big end bearings. Others argue that modern lubricants are so much better than what was available in the 70s and you don’t really need it. I have read that it’s particularly important on modified engines with stronger than stock valve springs causing greater friction between the fam and rocker surfaces. I personally err on the side of caution and would rather have ZDDP mixed in the correct proportions by oils manufacturers - apparently too much has a detrimental effect too.

 

2. Engine seal swells - The old reasons for damaging engine seals seem to be dispatched with: the first set of synthetics in the 70s were at fault and are no longer an issue / modern synthetics don’t affect it. Others say that the new plastics / rubbers used in rebuilt engines aren’t affected the same way. I guess I can buy both.

 

3. Oil weight - You can lose up to 5% bhp on the thicker oils such as 20w50. I personally like the 10w30 millers. Having said that, there is a classic racing oil I have in right now that I can’t remember the name of.

 

 

Lower winter / cold rating better for startup protection; lower summer rating improves flow and reduces drag. Some worry that the tolerances of our engines are too loose for thinner oils but others contend that engines properly rebuilt with 21st century tech are able to take it.

 

My personal experience has been that on the dyno we saw a small difference in oil drag - but I can’t recall the exact percent the tuner quoted.

 

4. Diesel engine oils - some contend that the detergents in diesel oils are designed to suspend combustion deposits / particles for longer in the oil and are bad for gumming up your engine, others swear by it.

 

5. Intervals - A pattern of consensus appears across various Z related discussions that we should change our oil every 3k miles and filters every 6k. My oil is done annually so it’s closer to 800-1000 miles but the filter is always changed (they are cheap enough). Running an oil catch tank, it’s amazing the sulphur smells that can come from the juice / gasses inside it. All of these combustion by-products are sitting in your oil in the sump in the winter and being pumped about when you run your car.

 

Also there is the argument that over time, the polymers in the oil are broken down by these by-products. This is why on my diesel Q5 i use long life oil but change it annually at around 8k-9k miles. Long life servicing by the PO caused the turbo oil feed pipe to gum up and killed the turbo (new turbo for free by Audi well outside of warranty - they only charged me for an oil change, what a way to gain a lifetime of my loyalty)!

 

Interestingly, many modern engines are designed with loose cylinder tolerances (read designed to consume oil) to reduce parasitic losses for the purpose of improving fuel economy and use the oil to achieve a good seal - also interesting to note that these same engines use 5w30 and not the thicker oils!

 

I think that covers what I’ve learned to date.

 

Would be interesting to know what your go to oils are and why you like them.

 

(Apologies for any typos, my eyes aren’t fully focussing today and my autocorrect is a little too keen for my licking!)

 

 

[heyitsrama]

What’s your oil catch setup look like? 

[AK260]

I don’t have a photo of it on my phone and away from the car at the moment but if you look closely at this photo (which I seem to be uploading everywhere) you can see it bottom left ...

 

 

If I did it again, I would get a baffled one. It’s a 0.3L one. It fills a third before each service.

 

[ETI4K]

I think the reason there's so much controversy about the particulars of oil (and SO many things) is because there's no obvious and clear BEST product for everyone's situation.  If you used the forums' "best" and "worst" oil, I'd doubt you'd see any significant difference unless you were running that motor for 100,000 miles per year.  At that point, you likely have to measure differences in wear with equipment better than .0005 indication.

A friend gets so wrapped around the axles about this sort of controversy that becomes paralyzed and cannot take a decision.

For the record, I pulled my 73 L24 at about 130K miles in mid 80s for a refurb.  There were no real problems,  just looking for optimum performance.  Original honing scratches were still present, seals were still in decent shape (most were hard but still keeping oil on the correct side - for the most part.  This was all based on technology that is now 40 years old.

Maybe it's a bit like the guy who bought a new H&K and ran 15,000 rounds through it before he cleaned it.  It continued to operate properly and well.  Lubricant technology development in the intervening years has become quite sophisticated and yielded amazing improvements in friction and wear reduction.  

I'd probably bet that the lowest cost crap oil you can find at AutoZone would far surpass the performance of the best oils of the day 40 years ago, which suggests that decent oil today should keep them running well past our life exoectancy, but that's just me, and I've had a cocktail!

[240260280]

 

[240260280]

 

[AK260]

Very interesting, thank you! In a tangential way, it’s convinced me I need an oil cooler ;) because when you do a 1000 miles per year it’s really important!! :p

 

Actually on a more serious note, it does go to demonstrate the importance of getting the oil up to temp before hammering it. Especially in turbo applications where the spindle is “floating” on a film of oil between it and the bearings while doing 60-90 Krpm!!

 

What I really want now is an oil temp gauge, because when you do a 1000 miles a year .... ;)

 

 

So what I’m taking away from all this is that:

 

- synth oil is OK.

 

- ZDDP is good to have even if modern lubricants are much better than 70s oils.

 

- A low viscosity oil is better for cold protection (obvs, I know but that freezer test really brought it home)

 

- the oils degrades fast with heat, so any way of keeping the oil temps down is beneficial + frequent changes.

 

Here is my cheap attempt at taking a degree or two off the oil - it’s something they use a lot in airplane engine air cooling applications. It gets too hot to touch, so it must be doing some good. I plan to use a small air duct to channel air to it.

 

[Dave WM]

that's an interesting oil filter cooler, can you tell the diff in the pressure with it on vs off? that is once you get to sustained operating temps?

I like the idea of the alum oil pan, just don't like the $$$ for it.