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MG MGB Technical - cold pressure

hi all,
had to be careful how far i pulled choke out on my C
on this cold morning as the gauge went off the clock. past 100. is this a problem, should it go that high.
thanks bob.
Bob Taylor

100 psi is very high. What oil are you using? Could be the relief valve is sticking when cold, but not familiar with the C engine.
Allan Reeling

penrite 20-60. pressure on tick over went to 60 lbs after few minutes.
Bob Taylor

Bob, I drive V8 powered MG's, those pressures are unknown in a Rover V8 , even with 20w 60!! Worth pulling out the relief valve and spring and giving a clean and looking for excessive wear which could cause the sticking.
Allan Reeling

The C should have an electrically operated oil pressure gauge. It was only used by MG from '68 to '70 due to problems of inaccuracy. The sender can often be the cause of a false reading and they're not a cheap item to replace, about $100. It's very common, with B owners of that era, to convert over to the mechanical version of that gauge. They're interchangeable. RAY
rjm RAY

Had that same sort of reading running 30 weight many years ago and winter caught up with me, and the car got parked outside a friends house overnight, instead of in my garage I was keeping heated to 45^F. 4 or 5 qts of oil takes much longer to heat up to operating temp than does the engine and cooling system. A 100 watt light bulb kept on overnight (car in a closed garage) before starting will contribute quite a bit of its heat output to the oil. This is the sort of thing people are talking about when they say much of engine wear is at start up. Cold Oil! Pre-heating oil in an engine prior to starting up greatly reduces wear.
S Cole

"The C should have an electrically operated oil pressure gauge. "

The North American spec MGBs had electric oil gauges from 68 to 70, but UK cars never had it and ket the dual gauge until 77. As it was part of the padded dash for North America, weren't UK MGCs the same as UK MGBs?.
paulh4

you are right paul, mine has same as MGB. C was ok this morn, went up to 80 then settled to 60 after couple of mins. must of been sticky valve.
bob.
Bob Taylor

When was the oil last changed?
Michael Beswick

september. had full service
Bob Taylor

Thanks for that bit of information, Paul. I simply "assumed" that the C oil pressure gauge, on UK vehicles at that time, was the same as the US model. Never assume. RAY
rjm RAY

Why 20/60 oil- that's very thick specially in your country and with an oil cooler, I would think too thick
Something like a good 15/40 would be much more suitable

willy
William Revit

20W too thick?
S Cole

60W. RAY
rjm RAY

The upper reading is not followed by "W", as W stands for Winter. 20W is SEA 20winter. . A multigrade listed as 20W 60, behaves like SEA 20 when cold, and SEA 60 when hot. i'e'. it holds a slightly higher viscosity at full operating temperature and operates somewhere in between at different temperatures. It is NOT "thick" as such. I have to say I used the Penrite 20w 60 in one of my V8's, in summer, to see if it held a bit more oil pressure when hot. Couldn't say the difference was significant.
Allan Reeling

The dichotomy for me is whether to go for 15W/40 in my V8 and suffer even lower hot pressures, or go thicker and suffer an even longer pressure rise time!
paulh4

Oil viscosity is a complicated subject, and to say that a 20W/60 is thicker than a 10w/40 is too simplistic. There is a very good explanation of it all on the link below, but if you can't plough through all that theory, scroll down the page to the heading "What is a multi-grade oil?" and start there. Very interesting.
http://www.kewengineering.co.uk/Auto_oils/oil_viscosity_explained.htm
Mike Howlett

Allan
That's how I understand it
A 20w60 oil for example
The 20w means that this oil is the same viscosity as a straight cold 20 grade oil when cold and the same viscosity as a straight hot 60 grade oil when hot

My previous suggestion of a 15w40 being more suitable was based on needing a thinner oil at startup to reduce excessive oil pressure/resistance hence the suggestion of a reduction to 15 and also 40 weight should be more than adequate for a lazy car like a C with an oil cooler fitted as they have----maybe a10w50 even
Think of the load on camshaft and oilpump gears etc.
I can't think of a reason that would convince me to put 60 weight oil in an engine unless it was a racer with no oil cooler but even then a 50 race oil does the job
willy
Personally' I'm using 0-40 Edge in most things now and I'm quite happy with that -Turbos love it
William Revit

Willy,
Yep, I get it! The thing with Rover V8's, which have the old oil pump driven off the camshaft skew gear via the distributor gear, is also the load put on those gears. It's accepted that the very highest psi you should ever see is 60, I worry if I see that even!
Allan Reeling

A option for the B series engine is to replace the piston with a 9/16" ball bearing. This overcomes the sticking problem (Peter Burgess modification). Not sure if this mod works on C series engine?'
Mike
Mike Ellsmore

Mike,
Definitely works on a B. It does cause a few fluctuations, presumably because it can react quicker than a torpedo!
Allan Reeling

Back to the oil .. In my experience the Penrite 20W60 is not 20W at all, and is much thicker at cold temperatures than other 20W oils. Try pouring it in cold weather, it is like treacle compared to other similarly rated oils.

What caused me to investigate this was almost complete lack of oil pressure on start-up on an icy morning, too much pressure drop across the cooler. This was on a newly rebuilt engine, only 250 miles on it. Problem went once the oil warmed up (took a while to achieve this with no load). And went completely when I changed to another 20w oil. (20W50, but the 50 (or 60) is the high temperature figure, the 20W should be comparable if the labelling is to be consistent and make sense.)

As the engine had just been rebuilt for a forthcoming marathon rally, I removed it and checked the bearing shells. All had been damaged.
Paul Walbran

100% agree Paul - My boo boo was running thick oil in a B series engine on which I had fitted by mistake (or dumbness)the combination of an oil filter housing without a bypass valve (Austin1800) and an oil filter without a relief valve - Therefore no relief (bypass) at all--
At full hook there just wasn't enough flow through the filter and no bypass to help
I still have what was left of the crank--
I had an oil pressure light sender in the block and the gauge into the filter housing
The light came on, so had a check of the gauge and it was sitting on 60-70 so kept at it-BIG mistake
After the rebuild I ran a filter with a bypass in it and some nice runny oil and all was well
I'm a converted runny oil fan now
willy
William Revit

Mike, to say 20/60 is thicker than 15/40 is too simplistic--no it is not. That Pentrite oil may seem thicker when poured out the bottle on some cold day, but it really should not be that way. MW Oils get their (1st #)viscosity ratings at low operating temp, or 85C I believe. At that temp an oil with a higher number rating is going to be thicker. Oils companies often give detailed specs on their oils and include one spec that indicates the pour thickness. A multi weight oil is the "thickness" in operation of the first (lower) number, and additives or other trickery allow it to behave like thicker oils when the oil gets towards the upper end of its operating range (105C going from memory). The actual oil flowing in the engine does not ever get thicker, it just thins out less, the higher the 2nd number. But you are along the right thinking that in certain (likely cold) conditions a particular oil can be thicker than expected, until things start heating up. I think it a good idea (better than nothing) to use a 100 watt light bulb under the sump pan overnight before starting when in a closed, but very cold garage. A proper plug-in oil heater is better. Oil takes longer to heat up than coolant or the metal parts of the engine, once it is fired up. Likewise, once hot, oil holds on to the heat longer than the block or coolant. Any time you can add some heat to the oil prior to cold startup, it is a good thing. When the US Lend Lease gave piston engined fighter planes and bombers to the Russians in WW2, they hated "wasting" fuel on warmup, like they felt we did. Instead they used oil heaters, and kept it hot until startup, at which time they were gunning it down the runway to take off.
S Cole

So if both oils are at 85C, isn't that going to make the 20W/60 thicker than the 15W/40?

Pre-heating the oil in WW2 fighters in Russia was probably as much to do with aiding starting as anything, given their winter temps.
paulh4

Both oils @ 85C, the "higher number rating" is thicker, yes. The 20W (20/50)thicker than 15W (15/40) at temp.
Russians pre-heated oil in summer, too, and specifically done to avoid using fuel for the typical "warm up" prior to takeoff. Start engine(s) and take off immediately at full throttle. The US aircraft makers were not thrilled with the Russian method. Any pre-warming of oil (summer or winter) will dramatically decrease the amount of wear that occurs in an internal combustion engine at startup, as the oiling system is designed for working at 85C to 105C, not ambient temp.
As for how Siberians started engines in winter, that's a whole other topic, but warm oil would certainly help.
As I said already, a lot of the engine wear that occurs in our cars at cold startup can be avoided by keeping the oil warmer before (starting), no doubt about it. Any oil temps up closer to operating temps at startup is better than oil temps down farther away from operating temps at startup.
S Cole

Check oil gauge calibration. You can pull the needle off and adjust it properly on a mechanical unit. Electric senders are not reliable.

The mechanical oil pressure gauge can be calibrated using air from a calibrated air compressor.
Glenn Mallory

I can imagine being able to 'adjust' a low-reading gauge if the spring-return tension was pushing it hard against the end-stop. But if a gauge was reading 30 or 40 psi high, and it was simply needle position, it wouldn't return to the end-stop when the engine was stopped.
paulh4

This thread was discussed between 30/11/2016 and 27/12/2016

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