My 1990 F-250 351W has been ran with Castrol 20W50 for most of its life. It has 213,000 miles on it. My buddy says that is too thick for cold weather like I have here in Oregon. I am reluctant to switch at this point as everything is fine and it purrs like a kitten. Should I switch to a 10W30 or something else? I have heard horror stories when messing with the diet of a truck with this many miles. Am I crazy to think that? Let me know what you think, brands and weights etc.

Thanks

 

How cold does it get up there? How does it start on those coldest mornings?

Not sure why you ever ran 20w50, when the manual probably tells you to run 10w30.

Not sure if it matters dropping down to thinner oil after running something that thick, but get a real oil pressure gauge and go to thinnest you can still get spec oil pressure, which for many 90s Ford V8s is around 40-60 psi at 2000 rpm hot. You can look up in Chilton's manual to be exact, but what I posted should be close. But do not go thinner than 30 weight.

 

That is what was being used when I bought the truck 6 six years ago. I have switched oils before in other trucks and dealt with seepage and leaks etc. I guess I have no good reason to run the stuff. Just scared of change I guess.

 

Sorry,

Right now it is in the 20's at night. Teens is common. We can get down to 0 for a week or so every now and then. It starts fine in the morning, at least it feels like it starts fine. I just don't want to be using this thick oil just because the guy before me did. That is a pretty bad reason.

Thanks

 

I thought you said it got cold in oregon.

 

If you do change oils, keep in mind that many of the current API- SM grades may not be backwards compatable with your engines valve train design requirement for % ZDDP, barrier lubrication.

So make sure what you choose is backwards compatable with the specified service grade called out in your owners manual.

There are some duel rated gasoline/diesel lubes that still offer elevated levels of ZDDP & are in the 10W-30 range, that would likely be suitable for your engines valve train design & your operatng temp range.

The lower first number will offer up easier cranking during cold weather, so that will make it easier on the battery & starter motor & the faster cold temp oil flow, will be kinder to the engine on those high rev cold starts.

The second number in the 30 wt area would likely improve flow rates, after the engine has warmed up & ease the pumping strain on the oil pump.

A lower viscosity will probably improve on fuel consumption too.

If you stay with the same brand lube, I should think you could lessen the odds of stirring up any trouble.
If the engine isn't worn too badly, it should tolerate the change to the specified lower weight lube, without being noisey.

Just some more thoughts for pondering.
Let us know how it goes.

 

Thanks for all your help. I am going to change the oil later this week and will let you know how it goes.

 

20w50 way to thick. Too much internal resistance, especially in the crankshaft, bearings and lower end of the motor. You are not doing your engine any favors running this oil, it will start and run, but it's working needlessly harder than it should, or has to.

I would use a quality 10w30 oil in this engine. It will help your engine develop peak performance, fuel mileage, immediate start-up cold lubrication, and help your starter and oil pump work better, especially when cold.

Use a good 10w30 from Chevron Supreme, Mobil 5000, Phillips 66 Trop Artic, Conoco, Kendall GT-1 or CITGO Superguard. All quality oils at the bottom tier of cost per quart.
Sunoco and FormulaShell motor oils as well.

 

From my own experience, changing oil weights even after 100k miles with the same weight did not cause any oil consumption where there was previously none.

20w50 seems heavy for the temperatures you listed. But it's hard to say it's a detrament with as many miles have been logged with it. One thing may be in you favor though. The current motor oils with higher Viscosity Indexes have lower pour points than the previous oils 10-15 years ago.

So I would have to say that even if your engine lasts 600,000 long strong miles, that 20w50 is going to kill it!

 

Go down one step to 15W-40 and see how oil pressure and consumption is. It is rated for cold cranking down to +4 degrees F. I would not jump to 10W-30 with over 200K miles and after a diet of 20W-50.

Jim