MG "B" Series Engines and Oils

Status
Not open for further replies.
Joined
Nov 23, 2015
Messages
2,244
Location
US
Hi Everyone,

I'm new here, and getting ready to dive into an oil change on what is to me a new car-a 1970 MGB.

The subject of oil for these cars has been beaten to death on MG-specific fora, and some searching here has lead me to some differing opinions and advice.

Many folks on the MG sites suggest Castrol GTX 20W-50, and the primary motive for this is the supposed ZDDP content. I've also received some conflicting information about it having been reduced.

Furthermore, I've read some linked papers I found in old threads here that discuss how important(or unimportant) ZDDP content is in flat-tappet engines like the B series.

So, before I buy oil for this change, I thought I'd ask here about what folks suggest. I drive the car frequently and usually for at least moderate length trips(often 60-80 miles) but don't thrash and also don't rack up a huge number of miles on it. Thus, I expect to be changing the oil more as a function of time than number of miles.

For some background information-the previous owner told me that he changed the oil shortly before he sold it to me(although since I don't know how long "shortly" is I'm getting anxious to do it myself despite the oil looking clean) and used Castrol 20W50.

The engine will reach about 65 psi within a 20-30s of starting up, and then drop to !50 psi at idle when warm and back up to ~60psi when at speed. This is consistent with a "good condition" B series engine.

So, with all of that out of the way, can anyone suggest an oil that would be a good match for this engine? The factory specified either 20W50 or SAE 30(for basically everything, including the transmission and the carburetor damping oil), so am inclined to stick with a 20W50 but am open to other weights if they would provide some real benefit.
 
When we had a MGB, it got a constant dose of GTX 20w-50 because oil disappeared fairly rapidly in the B. The rule about MGs is that "if it ain't leaking or burning oil, there ain't no oil in it."
 
I'm probably jinxing myself in saying this
smile.gif
but mine is as tight as can be. It doesn't leak a drop of oil(the clutch hydraulics are a different story) and burns only a minimal amount. In the time I've had it-and probably about 1000 miles of driving-I've watch the oil drop from just below the "max" line on the stick to probably 3mm or so over the "min" line.
 
To try and combat the leaks, I am using Valvoline Maxlife 10W40 and a bottle of ZDDP PLus for the flat-tappet engine (note: Rislone engine oil supplement with zinc is another option (stocked at Advance Auto Parts)).
 
Last edited by a moderator:
Many, many owners use 20w-50 or 15w-40 with no cam or tappet issues.

The 'B' series was a very robust and uderstressed engine, in normal tune, the cam is not too aggressive nor do the single valve springs exert high pressure.

The oil you are using today is Streets Ahead from what was used in the car when it left the factory.

Is it an older 3 main bearing engine, or a 5 main engine?

Regardless, most 'B' shipped to North America were fitted with an Air to Oil, Oil cooler (seemingly for NO good reason)
Homemarket models that were often in a higher state of tune and were invariably driven harder (on Britains motorways) did not have this, and suffered no ill effects, even with the Oil of the day.

If the car were mine, I might do away with it and/or fit an oil temp gauge, or use an Oil to coolant heat exchanger (as I do on my Triumph)
 
GTX 20W-50 was the go-to oil for many decades. Are there better oils out there - yeah. Does the B need better oil - maybe. Depends on how long you want it to run w/o a rebuild...

Are inclined to allow synthetics? Will older MG gaskets and seals live with syns... If so, maybe Pennsoil Ultra would be a good choice.

If no pure syn's I'm inclined to go Mobil Delvac or Delo400 15W-40 and see how it goes. That's what I have been running in my "euro" cars for a while
smile.gif


My wife's Jag 6 has 188,000 miles on Delo400 after it came off warranty. No issues
smile.gif


I ran all my Volvo's on Delo. One went 283,000 before being donated to Purple Heart ... Was trying to get 300K (and the badge) when it would no longer pass smog and I did not want to spend the $$ to get it there ...
 
Thanks for the additional responses, information, and specific suggestions.

The engine is the original 5-main(I think they changed from 3 main to 5 main in '65 or so) and does indeed have an air oil cooler. I do know that the engine stays fairly cool as a general rule. The temperature scale isn't graduated, but the needle generally stays to the left of center(the "N" marking) unless I'm at sustained higher RPMs(i.e. on the interstate) in which case it might stray over to the "N."

My inclination is to stay away from synthetics. My daily driver('04 Lincoln LS, 145,000 miles) has been running nothing but Mobil 1 for as long as I've owned it, but I'm a bit worried about putting synthetic in the B engine.
 
The standard dash mounted temp gauge monitors coolant temps.

Oil temps can vary from your coolant temp, and typically take a good deal longer to reach optimal temperature (175f-220f)

MG did make a sheet metal shroud to blank off the cooler (winter?) But honestly, I have not known a Road Car that needed or benefited from the thing in the first place.

I remember talking to an ex Abingdon engineer about it. His only explanation was, Back in the day, Americans put 10w-30 in everything (which was considered too thin in England) So an oil cooler was fitted as some sort of precaution.
 
But of course thicker oils have higher bearing temps due to increased drag, so how does that help ...

And then Porsche lists Mobil 1 EP 5W-50 for current motors on the A40 list, so that fly's in the face of the thinner oil crowd
laugh.gif
 
Thanks for the additional info on the oil cooler.

Interestingly enough, Moss actually sells an aftermarket oil cooler kit that-for all intents and purposes-looks like the factory cooler except that it contains a thermostat

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29833

Granted, for the cost of the kit(the $379 price doesn't include a radiator) I'd rather just bypass the thing entirely since I agree that it's likely not necessary.

I'm just hesitant to start messing with it since-as I said-the engine currently doesn't leak.

I was hoping that Moss might have the cooler blank, although they don't seem to. I'm sure it's nothing especially fancy, so I might give making my own a shot.

I'm constantly amused by the fact that a car designed and built in a country with a reputation for being cold and rainy seems to fair poorly in both conditions
smile.gif
 
Last edited:
I am going on 20+ years of Mobil1 in my TR6, usually 15w-50, but have also used a mix of their 10w-40 and 20w-50 M/C oils for the higher ZDDP levels. I talked to Mobil's tech folks who indicated that mixing the MC oils to get a thinner result was OK. Interesting observation is that the MC oil mix doesn't generate as high idle pressure as the 15w-50 when cold but maintains the same idle pressure when hot.

My '72 Rover lives on M1 15w-50.
 
Hi,
bunnspecial - I have some considerable experience with the "B" Series engine. In their early days I saw them go out to 350k before overhaul or major issues. We used 20W-20, 30 or 10W-30 lubricants and the results were always excellent

In your case I would suggest using a 15W-40 late series HDEO - I used a synthetic 5W-40 HDEO in the last MGB I owned - I sold it in 2003
 
Thanks again for the continued good advice. I went ahead and went with the VR1 20W-50

Also, before actually ordering the oil cooler block, I thought I'd do the "low tech solution" and wired a piece of cardboard in front of the oil cooler just to see how things would change.

Although I don't have any direct way to measure oil temperature, I did notice that my idle pressure dropped considerably faster on warm-up and that when up to temperature the idle pressure came down to about 45 psi. That makes me think that the oil was not only warming up faster but also reaching a higher temperature.

If I'd had time, I would have drained the oil as soon as I'd pulled into the garage and measured it-that's probably the best way I have now to get a temperature.
 
Last edited:
Originally Posted By: BrocLuno
45 psi at idle is great. I'd take 15~20 psi and be happy. Your motor is pretty tight
smile.gif



That's good to know-I was actually a bit surprised when it went below 50!

Granted, the low end torque on a "B" engine isn't great and I've been known to stall it on hills more than a few times. Thus, the orange low pressure light is not an unfamiliar sight to me.

In any case, I finished the oil change along with several other jobs. I'm slowly working my way through a tune-up, and gave the oil a good hour to drain while I worked on the carburetor dash pots as well as the front end. Even at the end of an hour, I was still getting occasional drips of nasty, dark looking oil out of the sump-I suspect that having the front end inclined as sharply as I did helped get the more out of the cooler.

4 quarts got me to the top of the stick(the spec sheet lists "9 Imperial pints") although that was before starting the engine and getting oil circulated through it. I'll let things settle and check again tomorrow after I've dropped the front end. Cold pressure at idle after the change was running a shade over 50 psi.

If nothing else, I'm glad to be rid of the big ugly orange filter
smile.gif
.

Before I do that, though, I also need to drain the transmission, and the drain plug is being quite stubborn(I suspect it's never been out). I'm pretty sure the transmission dipstick had also never been out before I pulled it a few weeks ago. Refilling the transmission should be fun-I cobbled together a funnel for it, but I'd still like to know who thought it was a good idea to have it fill from the passenger footwell
smile.gif
 
From what I have seen with stock, US spec '[censored]' without a cooler will seldom see over 200f, even being driven hard uphill.

I say this as a friend and I fitter a Toyota 5 speed to a 'B', that he often drove quite hard. (80mph + for long periods. Like Vancouver to Lubbock Texas!)
We wanted to see how an O/D 5 speed would effect oil temps.

If I sound a bit down on Air to Oil coolers, it's because back in the 70's, I once had an OC hose let go, comming home from work, in rush hour traffic!
It was unfortunate the car DID NOT catch fire :-(
 
Originally Posted By: expat
From what I have seen with stock, US spec '[censored]'


I guess the censor will not allow me to use the plural of 'B'

mad.gif
mad.gif
 
Usually called a BMC B block - these engines were used in a lot more cars than MG. But i guess the US didn't see much of the badge engineered BMC range.
 
Status
Not open for further replies.
Back
Top