Question about 20W-50
- Thread starter The Shape
- Start date
- Status
I value this man's advice. His past posts indicate to me that he is a very knowledgable mechanic and so, while it probably won't hurt anything this go around, it might be a good idea to play it safe and dump the 20w50 (call it a flush, after all, oil is relatively cheap) and refill with 10w40. You could leave the filter on as the little 20w50 left will dilute with the 10w40.
We have too many cooks here and I am as guilty as the rest.
I would run 10w40 in it. For now you could dump half the 20w50, add in the equal amount of 10w30, and you would end up with about a 15w40. Saves dumping all your oil. This will do well for the summer.
I would run 10w40 in it. For now you could dump half the 20w50, add in the equal amount of 10w30, and you would end up with about a 15w40. Saves dumping all your oil. This will do well for the summer.
- Joined
- Sep 28, 2002
- Messages
- 39,799
Leave it in ..don't worry. When you're ready to switch ..switch. This would be no different than using your 10w-30 at some cooler temp that you surely experience at some point in the year.
In the future, I wouldn't worry too much about detergency in a given oil. Oils may be better or worse as far as keeping things clean ..they aren't all that great at cleaning things already there ..at least the stuff that's been there for a while. You'll get some suspension of stuff ..but only to the limit of the oil's ability to suspend it. It then has less capacity to "wipe its own arse" so to speak. It's then a balance (or imbalance) of "stuff" production and stuff suspension ..all varying on how long you leave it in.
The only weakness that I heard in the 5.0 was that they bottom ends blow apart when you mod them too much. Less stout, by far, to the 351 block. There was some late 70's issues that I recall with 20k seizing of some small blocks (I forget which displacement). Now surely there may be inherant weaknesses in the design ..but they don't seem overly apparent in typical useage
Relax. Enhance your calm ..and be well.
In the future, I wouldn't worry too much about detergency in a given oil. Oils may be better or worse as far as keeping things clean ..they aren't all that great at cleaning things already there ..at least the stuff that's been there for a while. You'll get some suspension of stuff ..but only to the limit of the oil's ability to suspend it. It then has less capacity to "wipe its own arse" so to speak. It's then a balance (or imbalance) of "stuff" production and stuff suspension ..all varying on how long you leave it in.
The only weakness that I heard in the 5.0 was that they bottom ends blow apart when you mod them too much. Less stout, by far, to the 351 block. There was some late 70's issues that I recall with 20k seizing of some small blocks (I forget which displacement). Now surely there may be inherant weaknesses in the design ..but they don't seem overly apparent in typical useage
Relax. Enhance your calm ..and be well.
How's the PCV system? IE excessive crankcase pressure will put undue strain on the seals.
Something easy to rule out anyway..
- Joined
- Sep 28, 2002
- Messages
- 39,799
Yes, I do. Go here and hit the viscosity link. Get the specs for your respective oils and plug them in using the 40C and 100C viscs. Then plug in your reference temp in the lower table. This will allow you to compare the 10w-30 at your cooler temps and your 20w-50 at your current temps.
I don't know what your cooler temps look like ..so it's hard for me to do the math for you.
I think that you will find that there is common ground where they are both at the same visc. For example 45 w/10w-30 and 85-90 with the 20w-50 may be the same (pulling the temps out of my behind).
I don't know what your cooler temps look like ..so it's hard for me to do the math for you.
I think that you will find that there is common ground where they are both at the same visc. For example 45 w/10w-30 and 85-90 with the 20w-50 may be the same (pulling the temps out of my behind).
I just said to heck with it. I went ahead and changed my oil this evening. I went back with plain Castrol GTX 10w-30 like the manual calls for. Even though my pressure may be a bit low at idle I guess untill it starts ticking I don't have anything to worry about.
Gary, EXCELLENT link. I bookmarked it. Thanks!
OK, have it your way..... you have several members posting thier opinions on use of 20w-50 oil. I think 1988 still falls under 'modern'. Since you obviously feel it is 'like the first V-8's', Then why even ask the question. Just run that 'owners manual' recommended 20w-50. Just make sure it is API SE/SF, so it fits around that 1988 year........
That motor is old school, no doubt.
Wow Gary. You really put it together. I never ran that chart in that way, but always used it for blending oils.
A 10w30 at about 170F is going to be as thick as a 20w50 at 210 F, so all of us are running "20w50" for part of the time before our engines are warmed up. Even those supposedly delicate Ford modular OHC engines with their 5w20 are going to be in the 20w50 range for a bit.
A 10w30 at about 170F is going to be as thick as a 20w50 at 210 F, so all of us are running "20w50" for part of the time before our engines are warmed up. Even those supposedly delicate Ford modular OHC engines with their 5w20 are going to be in the 20w50 range for a bit.
He said the engine was a 1987, and that it was same design as 1968. I say regardless, it is a 'modern' engine. Even the original Chevy small blocks had changes from 68' to 88'......it is not something out of 1950...
Aw screw it...
- Joined
- Sep 28, 2002
- Messages
- 39,799
Yes, TallPaul. That's why, without knowing the oil temp, it's hard to say what "true visc" you're running in your engine. That's why short trippers tend to reap the major benefits from lighter oils in terms of fuel economy, IMHO. They're closer to "spec" visc over the duration of use. For a dedicated short tripper, you could probably go down a grade without every being out of spec
Even if the VI doesn't plot a linear path at lower temps, you can assume that your oil will at least be at 40C and approach the 100C figure at some point in the event..and dwell somewhere in between. If they have any common visc between those two figures (a different temp figure for each oil) ..then you've been running, for at least a limited amount of time, at that higher oils visc.
Even if the VI doesn't plot a linear path at lower temps, you can assume that your oil will at least be at 40C and approach the 100C figure at some point in the event..and dwell somewhere in between. If they have any common visc between those two figures (a different temp figure for each oil) ..then you've been running, for at least a limited amount of time, at that higher oils visc.
The Shape was getting about 38 psi with 10w30 hot and 50 psi with 20w50, so all he has to do now that he has switched back to 10w30 is observe when his 10w30 is reading 50 psi and he is approximately at the 100C viscosity of a 20w50.
However, one can get too thick if the oil is bumping the pump relief valve open at full operating temperature. The Shape's 10w30 very well may be around 50 psi at cold start.
However, one can get too thick if the oil is bumping the pump relief valve open at full operating temperature. The Shape's 10w30 very well may be around 50 psi at cold start.
- Joined
- Sep 28, 2002
- Messages
- 39,799
Yes, pressure should be a telltale way of determining "effective visc". He may never reach 100C in either ...but he can observe the peak and warm pressures. Where they are in common (at different points in the "start to warm" cycle) they are at the same effective visc. This does require the pressure relief to be closed for validity, as you stated.
Drove around this morning for a bit. Temps are already about 85 degrees. I am holding at about 20 psi when fully hot idle and around 38 or so at 2K rpm's. So I guess I will just stick with the 10W-30 in my "ultra modern wave of the future cast iron block pushrod V8" Anyway thanks for the advice guys some of you seem to really know your stuff.
- Status
Similar threads
