Can anyone venture wise commentary on whether large air cooled ci motors (like the after-market S&S or Ultima ranges, the +100ci), if being run in regularly hot temps (like 90F+, 30c+), can benefit from using oils like a 25W70 (like the Penrite Enduro) or diesel 20W40 (assuming regular oil and filter changes especially, shorter time-frame for mineral over synthetic)??? And if there is benefit from such oils in such engines, are those benefits lost or even downsides incurred when the temps come back down, say below 60F (15c) or even below 50F (10c)?

 

Well I'm no expert by any means but I have stayed at a Holiday Inn Express , sorry I couldn't resist. But back to your legitimate question. I built a 106 last winter in my 2010 SG before I traded and it was using a little oil after the build, so a friend suggested a straight 50wt so I tried that, wrong !! My lifters like to have never pumped up. Lifters were comps 850-1's by the way. Anyway I swapped back to 20w-50 and solved the problem somewhat but they were never the same after that. The reason for the oil usage imo was those paper thin rings on the wiseco pistons I used, never again but I think your 1st choice is way too thick. 2nd choice would be better but why not just use a good syn. 20w-50 and forget about it ?

 

The upper number of a multi-grade oil will behave like its equivalent single grade oil ONLY when temps are high enough to do so.

So, you could use (if it was available) say 20w100 and have the oil behave like a 20w at the appropriate temp. And as its temp rises, it will behave like 40w. As the temp rises further, it will behave like a 50w and so on.

If the oil's temp never get hot enough to cause it to behave like an equivalent 100w, there would be no benefit from using, say, as 20w100.

 

That's a good question and I would had to have stayed at a Holiday Inn to answer fully! But the short answer is that my oil query is generated by the Ultima 107 I have in my 1992 FXR being a real oil guzzler. I have used synthetic and mineral 20W50 (trying various brans, Amsoil, Mobil, HD etc) and she still guzzles oil. As best I can tell, there is no leak. Fortunately, changing oil (especially just oil change and not filter change) on an FXR is easy (oil tube accessed by unscrewing two bolts on left side cover), so the oil guzzling can be managed. But I was reading the specs for Penrite Enduro recently and at the end it says for oil guzzlers where 20W50 is specified, the Penrite 25W70 can substitute. Hence the curiosity question.

 

So at very hot temps there would be benefit? How got for a 25W70 to be beneficial? But below those temps, is anything being lost compared to 20W50?

Forgive my ignorance!

 

The 20w will be a little thinner than the 25w in the cold, before it warms up. I run 5w40 diesel oil in my v twin and all is good.

 

If you are using oil and it is not leaking, then you are burning oil. Changing to a heavier weight is only going to mask the problem, not solve the root cause of it.

 

I'll agree with Next In Line on this one. This what I was trying to do was shift to a heavier weight oil to slow the oil consumption down but in the end I think it was the rings on the pistons causing the problem. If engines are built with the right tolerances then we actually don't need the thicker oils period but I think the reason for the 20w-50 oils is more heat releated than anything. Look at cars these days, 0w-20 oil, crazy but it works, I know there not air cooled thus the reason for the thicker oil in our engines due to heat related break down etc. imo.
I also went to the Penrite web site and the oil has a lot of zinc (1500ppm) and the way I take it it's for a loose engine or a engine showing wear to slow the oil usage down. Anyway hope you get the issue worked out but sounds like it is what it is. I know a guy that has a Utima engine and the oil changing during the break-in is crazy, sorta make you wonder why that much changing to begin with.

 

In the old days, replacing rings and valve guides in Harleys was common. Do a compression or leakdown test and take it from there. I had to put new rings and guides in my '78 XLCH at 33k MILES.

 

A whole lot of bull **** in this thread, but not too many facts. Oil consumption is blow by, it means your top end is worn out whether you have rotted or worn valve seals, or you have 100k or more on the top end and the rings have had all they can give. A compression test will tell you this.


Extra zinc in your oil is not going to do anything to slow or stop oil consumption. Manufacturers put more zinc in their oil based on how much of it will be consumed during operation. Most good oils have less zinc in them because these oils are less likely to burn or use up zinc. Too much zinc in your oil is just as bad as too little. What you should be concerned about is potassium levels in your oil as that is what scrapes cam lobes and rollers on your lifters. A quality oil with 660ppm of zinc will work just as good as an OK oil wit 1500ppm of zinc.

Run 20w-50 in the fall, winter, and early spring, and straight 50w during late spring and the summer and you'll be fine. Stop over complicating this ****.