Question about 20W-50

[The Shape]

I just change dmy oil over to Castrol GTX 20W-50 for the summer. My car is a 1987 Mustang with the 5.0 V8 and 123,000 miles on it. My haynes manual calls for 10W-30 in warm wich is what I have always used. But since I have a slight rear main seal leak and it is so hot here lately (98 today with 110 head index) and all of my driving is stop an dgo in town driving I was thinking the 20W-50 would be safer. Am I wrong in thinking this?

The engine seems to show oil pressure just as fast on first morning crank up as it did with the 10W-30 it just holds better pressure when fully hot now. Ok for my main question is there ANY possibility of doing anymore engine damage with the 20W-50 vs. the 10W-30? If the 20W-50 is more likely to sludge up or cause engine wear I will swap back. I like the increased hot idle oil pressure I am seeing but don't want to chance any damage. I realize I may see a small decreas in MPG but that really doens't concern me.

 

[TallPaul]

Assuming you have a real oil pressure gauge (also with numbers), I am curious what hot pressure you get at 2000 rpm with the 10w30 and with the 20w50. Spec likely is 40-60 psi at 2000 rpm.

You probably are ok with the 20w50 though I would have been inclined to step up to a 10w40 first. For example, I was getting 35 psi with 5w30 and now am running 10w40 and getting around 42 psi. Good enough for me.

There are ways to deal with the main seal leak. Check discussions on AutoRx, but also consider that a high mileage oil is supposed to help with leaks over time. The process in either case is that the additive cleans off the hardened crud from the seals and then conditions the seal to make it more pliable so it once again seals as it should (assuming no physical damage to the seal). In this process it is possible to get more leaks as the "false seal" of crud is removed until the seal is reconditioned.

 

[The Shape]

Was getting about 37-40 p.s.i with 10W30 and now am seeing about 50 p.s.i fully hot with the 20W50 at 2K rpm's. But my problem was at idle with the 10W-30 I would sometimes dip below 20 with the 10W-30 and the lowest I see with 20W-50 is 25. This is using an autometer sport comp gauge. I am just wondering if there is any potential damage to be had from the 20W-50. As for the rear main seal. It doesn't bother me that much it isn't a huge leak anyway.

 

[TallPaul]

Well that is an excellent gauge, much better than my AutoGauge (Autometers cheaper line). I doubt the 20w50 would hurt and your oil pressure with it is good (not too high). Though I would probably run 10w40 in it. Below 20 is not supposed to be bad at idle.

 

[427Z06]

quote:

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Originally posted by The Shape:
But my problem was at idle with the 10W-30 I would sometimes dip below 20 with the 10W-30 and the lowest I see with 20W-50 is 25. This is using an autometer sport comp gauge.

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If you check the specifications on this engine you may find that a hot idle oil pressure of less than 20 psi is totally acceptable.

 

[The Shape]

So does that mean the 20W-50 will hurt the engine or..... I am getting more confused

 

[55Test]

In that kind of heat, I don't think 20w50 will hurt that engine. Ever consider running some 15w40 HDEO?

 

[Pablo]

I won't hurt your engine if temps remain warm and you do very conservative OCI's.

As for the suggestion from 55, I was gonna say the same.

 

[The Shape]

Oh I plan on running it only untill september when the temps drop back down a bit then I will swap back to 10W-30 or 10W-40. I just wanted to make sure I won't cause any damage for the three months I intend to run it.

 

[James408]

Instead of the 20w50 or 10w40 why don't you try Chevron Delo 400 15w40. You could probably run this oil year round in Arkansas. This oil is pretty tough, I use it in my 69 Firebird here in south Texas. I don't like 10w40. The 15w40 has a heavier base oil and will not shear as much as the 10w40. I was a skeptic when I came to this site and only used 20w50. I tried the Delo 15w40 and really liked it. Chevron states this oil is responsible for trucks making a million miles of life. Just my .02 cents.

 

[TallPaul]

Unfortunately, I don't think Ford gives an idle oil pressure spec. I am looking at my '84 Ford Truck shop manual for the 5.0 V8 and it only gives hot, 40-60 psi at 2000 rpm. But I think his idle is fine even at 15 psi.

He can surely run a 15w40, but many 10w40s would be good too--at least under SL they were (note Durablend ACEA A3 rated).

 

[The Shape]

Man there are WAY to many choices it gives me a headache LOL. I had thought of running 15W-40, here is why I didn't tell me if my reasoning is flawed because it may well be. I was under the impression that since the 15W-40 was mainly designed with diesel engines in mind that is was probably really high detergent. I was affraid this might clean up deposits around seals and cause leaks. I have seen that happen with snthetic oil on high mileage engines which is why I won't switch to synth on this motor. My only concern was if the 20w-50 could be so thick as to leave sludge or be to thick for the oil pump or anything that swhy I came here to see if there were any horror stories about 20w-50 LOL. With my mileage I am sure my bearing tolerances or not what they used to be. I see 20W-50 doesn't seem to be ver popular around here, why is that. Or there some really big drawbacks to using it?

 

[cyclic]

I ran that weight oil in my 88' 302 for years in the summertime and never had a problem.

YOu'll be fine, the 302 is a loose goose.

 

[Propflux01]

IMHO, even here, in Arkansas, 20w-50 is just too thick of an oil to run in any modern V-8. Personally, I wouldn't run any thicker than 15w-40, and would defiantely take that over a 10w-40. That engine was designed with 10w-30 in mind, and will run just fine with that. If your just using the superweight oil to slow down an oil leak, I would think your losing much more in pumping losses causing worse MPG than what your probably spending on top-up oil. Fix the seal, run your 10w-30.

 

[TallPaul]

Most here don't use 20w50 because it is pretty thick stuff.

My Haynes manual for '80 - '96 Ford Pickups has a table that shows all the oil weights and temps to use them. It shows 20w50 is acceptable for temps above 20 F. You should be fine, but next time you might want to throw in some 10w40 and see what your oil pressure is. You can run 10w40 (or 15w40) year round in your climate.

Frankly I think modern 10w40s are pretty robust and not likely to break down, especially on a nominal 3000 mile interval.

Oils more likely to clean out stuff from your engine include synthetic, high mileage, and heavy duty (diesel type). Most 15w40s are diesel rated, but Valvoline Durablend 15w40 is not (well nominally it has CF rating, but that is a light duty diesel rating).

 

[The Shape]

Modern V8???? The bottom end of my engine is no different that the first 302's that cam eout in 1968.

 

[The Shape]

Thanks Paul that table is the exact kind of info I was looking for. I believe the original owners manuals for these cars actually showed 10w-30, 10W-40 and 20W-50 as acceptable. I know they showed the 10w40 and 10w30 not positive on the 20w50. But then they changed there minds and the last few year models with this engine called for 5w30 or 10w30 only. I think this was probably to meet cafe requirements. If I was THAT concerned with gas mileage I wouldn't have bought a V8 Mustang LOL.

 

[Doug Hillary]

Hi,
most people do not realise that the 20w-50 viscosity was especially developed for use in the Austin-Morris (BMC) Mini in 1958/9. Of course this vehicle had an integral engine gearox that shared the same lubricant

In the nearly 50 years since then I have not seen many vehicles that required this viscosity as the ultimate lubricant

IMHO it is generally better to sacrifice some idling OP to the benefit of flow without the possibilty of triggering the by-pass up the rev range. But this may trigger the thick/thin debate - I sincerely hope not!!

IMHE these engines do perform well on 15w-40 HDEOs - they lived well too on the 10w-30 minerals they we designed for

Sadly the only way to stop leaks is to fix them!

Regards
Doug

 

[cyclic]

The 302 is NOT a modern engine design lol.

It's bullet proof, run the 20w50 and be happy.

 

[mechtech]

Over the years, we've seen that small block Fords have a weakness in rod bearings. They fail more than any other motor. They are skinny, but maybe there are other reasons.
20-50 probably is more than you need, and would induce too much internal drag.