Oil Recommendation for 74 MG

[Jim Allen]

I had a coupla Midgets/Spridgets with the A-Series engines back in the '70s. I ran 50 or 20W50 because I didn't know any better. Had the wonderful experience of on a cold winter start of shattering the aluminum oil pump housing (a weak point and not uncommon in "the day") due to over-thick oil. Requires pulling the engine to replace it as it drives off the back of the cam. Pulling the engine outdoors in winter was fun and only for the young and ignorant. ( : < )

If I had one today, I would run an HDEO 10W30 like Rotella Triple Protection or the T5 semi-syn (or DELO or some other 10W30 HDEO). You won't be too far off the mark with the 15W40 some people recommended but I think it's too thick... assuming you have your fuel dilution under control after the carb tweaks (the most fun part of working on these cars are the carbs) and considereing you have an oil cooler.

Heed Hillary's advice on the oil cooler. I doubt you'll be driving much in winter but you can overcool oil with an unregulated cooler even on a cool day and cause the oil to run super thick all the time. Oil too thick is as bad as oil too thin and don't forget the oil pump incident above. It's another argument for the 10W30 oil IMO. With the cooler, the oil will run 30+ degrees cooler than without at any ambient temp.

If you wanted to be totally accurate in your oil selection, you could hook up an oil temp gauge and monitor it. If you see stabilized oil temps under 200F in the operating conditions the car normally sees, your Midget is a good candidate for 10W30 because at 180-200F, its running in or near 40 grade territory anyway and a 40 grade is run either at the very tiptop of grade or well into 50 grade (depends on what exact viscosity the oil is within grade). IIRC, there is an oil temp port in the oil cooler adapter. I might be thinking of MGBs or even my old MGC. Might be worth checking and installing a temporary temp gauge for monitoring over a season.

Vizards A-Series book is a masterpiece! I bought it back in the '90s even though I no longer had an MG... just because it has so much general engine knowledge. If you have and A-Series engine, it's a must-have companion IMO! reading it is like getting a college degree on that engine.

 

[CATERHAM]

Gentlemen I'm late to this thread.

I agree a 20W-50 is usually too heavy for most older British engines (unless they are well worn) although that is what everyone recommends and tends to use.
I was at the annual British Car Day (www.BritishCarDay.com) last month which is only 5 miles from me. It's the largest British car show in North America and oil vendors are still selling 20W-50 and not much else.

One problem with the 20W-50 grade is that due to modern polymer technology the latest 20W-50 offerings are more shear stable and therefore thicker in service than the 20W-50 grade of 40-50 years ago. And if you've had you're engine rebuilt with tighter clearances it makes the grade even more unsuitable.

A Lotus friend of mine recently bought a series 4 Lotus 7 race car for vintage racing. It has the Ford (kent) cross-flow engine and he ran a dino 20W-50 (bought at the track). Maximum oil temp's are only 200F. The engine has the standard low pressure oil pump with a 50 psi by-pass setting. The recommended hot OP at high rev's is given as 35-40 psi. Unfortunately even when the oil is fully hot, he was in by-pass mode 100% of the time at high rev's.
Well you know where this is going. After 4 or 5 races this season he had complete engine bearing failure.
The good news is that he had the engine out and rebuilt in less than two weeks in time for his next race at Mosport. Yes he's still running the same ridiculously heavy oil, but now I've finally had a chance to have a chat with him so hopefully he'll start running something a lot lighter.

Yes he was quite defensive when I told him you cannot run an engine with the oil pump well into by-pass once the oil is up too temperature.
You can get away with it on the street when you're not extracting full power and you're just putzing around but it's a recipe for disaster on the track.

The oil I recommended he try (and it may still be heavier than necessary) was Mobil Delvac 1 ESP 0W-40 (HTHSV 4.0cP, 186 VI).
Unfortunately this PAO based oil is not available in the States.

One problem with the 20W-50 dino is it's typically very low 125 VI which exacerbates the oil's heaviness on start-up and also at normal operating temp's.
The higher VI M1 15W-50 is lighter at operating temp's and most 5W-50s are lighter still. Then there is Rotella 5W-40 and of course M1 0W-40 is lighter than that. If M1 0W-40 is still too heavy which is unlikely, there is GC 0W-30 while not lighter on start-up it is at operating temp's and the even lighter M1 HM 5W-30.
So there are a number of modern higher VI oils from which to choose other than a dino to find the something with the right operational viscosity.

 

[vintageant]

Assuming your friend's Lotus has an OP gauge, does this mean at 200F the OP never dipped below 50 PSI?

 

[CATERHAM]

Originally Posted By: vintageant
Assuming your friend's Lotus has an OP gauge, does this mean at 200F the OP never dipped below 50 PSI?

He does have an OP gauge which is how he new he was in by-pass at elevated rev's.
On idle and at very low rev's the engine was not in by-pass.

 

[Doug Hillary]

Hi,
CATERHAM - Your point is well made - 20W-50 is simply too viscous for most applications. People forget or simply don't know that is was developed for the integrated engine/gearbox BMC Mini - in 1959!

My aim has always to limit the by-pass period by choosing the correct viscosity for the application

A quick look at the historical data on my Porsche 928S4 shows these figures over about 160 readings

Gauge = Avg 185f Max 190
Hottest external location = Avg 200f Max 210 (both via Raytek MiniTemp reader)

Most engines (and drive line components) run a lower oil temp than Owners would believe!

Even my 500hp series 60 Detroit Diesel engines only showed a max of 233f during a long mountainous climb. Mostly they operated at about 200f. I used a 5W-40 synthetic HDEO