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MG MGB Technical - Is that oil cooler really a good idea?

This winter I am doing some work on my 64 three-bearing engine, and yesterday I cleaned out the oil cooler. Did not look good at all. What came out at last was very black and very thick...

That makes me wonder - in a country like Norway, with summer temperatures usually around 20-25 C (70-76 F), and 100 km/h (62 mph) speed limit, is the oil cooler keeping the oil temperature too low?Right now, I think about leaving it on the bench when I put the engine back in the MGB again.



I think you could leave it off, and get better cooling of the water in traffic jams (well waiting for reindeer crossing in Norway) .It really is a sporty looking installation though when you open the bonnet !
S Best

They are very difficult, if not impossible to get absolutely clean.

If you decide to stay with an oil cooler, I suggest you fit a new one, however they were an option in the UK so I do not think you need one.
Ian Buckley

I agree with Ian's suggestion that a new oil cooler would be a good idea.

Why not fit an oil thermostat:-


Nigel J S Steward

Oil coolers were eventually fitted as standard because lower oil pressures in hot weather were causing owners to complain fearing worn bearings. Fine when under way, but stuck in traffic on a hot day, particularly on RB cars with underslung coolers, it has no effect and the pressures drop anyway! It's probably completely superfluous for Norway, and further south.
Paul Hunt

I like the thought of an oil thermostat, except for the fact that it introduces several new places where an oil leak can develop!



Try obtaining a temperature reading, strips are available.

Sump temp changes appox 1c for 3c ambient.

If running without cooler you could try synthetic oil, better cold flow and can handle higher temperatures than mineral.


Enhanced performance engines produce more power by creating more heat to expand the atmosphere inside their cylinders in order to force the pistons, connecting rods, and crankshaft to do more work. This in turn places increased pressure upon their bearing surfaces inside the engine. This increased heat and pressure places additional strain upon the lubricating oil, shortening its useful lifespan. While the radiator performs the function of cooling the head and cylinders, it is the oil that cools the internal parts of the engine. While mineral-based oils are fairly efficient at absorbing and transferring heat, the more heat-resistant synthetic oils are relatively inefficient at this task. To assist in this function, as well as to help protect the lubricating qualities of the oil from breakdown, an oil cooler was fitted to all MGBs except during the 1975 through 1980 production years when power output was chopped in an effort to meet emissions regulations. US market cars had a 13 row cooler, and this should be considered to be the absolute minimum for an enhanced performance engine. If your car has one, be sure that it is hot tanked along with the other components and thoroughly cleaned out before reinstalling it. If you are replacing it or installing one for the first time, use one that has at least 16 rows and install a 200 degree Fahrenheit thermostatic bypass valve as overcooled oil can rob power and lead to accelerated wear. Because overcooled oil is thicker than it would be at normal operating temperatures, the piston rings will "hydroplane" over the oil and, on the upward stroke, scraping it into the combustion chamber where it will be burned, leading to carbon deposits and an increased risk of preignition. An excellent thermostatic bypass valve with 1/2" NPT threads is available from Perma-Cool (Perma-Cool Part# 1070). Perma-Cool has a website at .
Steve S.

Thanks, Steve. This was really interesting. Seems that a high quality oil thermostat and a new oil cooler is the way to go.


Synthetics should be about 10-20% more efficient because of the film thickness and thermal properties, apart from M1 which seams to underperform other Synthetics in this area. Top quality Synthetic oil (the best types are used in the heat of jet engines) hardly shear only additives are used up, unlike mineral which quickly shears down from a 20W50 to 20W40 etc.


I use Mobil 1 in all of my cars and I agree that it resists shear better than the mineral-based oils. However, I prefer to think in the long-term. I use the oil cooler to help get rid of heat. Just because the oil can stand the heat without breaking down doesn't mean that heat can thus be ignored. Engines last longer when operating tolerances stay within engineering specifications, even when the oil is of the best quality. This being the case, I consider the oil cooler to be a wise move for a car that's going to be kept for many years.
Steve S.

If you don't want to spring for the cost of a thermostat plus replumbing consider making up a cover for the winter months. Even an old hat or tea cosy would do


Out of interest which M1 do you use as a lot more choice in US(UK only 0W40 or 15W50).

As Tore is in cooler Norway and does not push car that hard, I was agreeing with Paul H's point as maybe not needed and an added complication and expense, and suggested temp strips as a monitor, and Synthetic to give good flow in Norways winter but protection for any potential temperature rise.

An added advantage of a cooler is a slightly increased oil capacity, however the reasons for black and thick gunk may be down to low temperature infrequent running or type of oil used. So I would still check oil temperture.


I have a thermostat in the oil cooler circuit. It is supposed to open at 85 celcius I think. Here in Scotland, it virtually never opens, except in traffic on warm summer days (20 celsius). Other than that my oil cooler is cold the whole time. I wonder what the contents are like.....?

Previously I had a 1275 midget (wonderful car for short trips). Putting an oil cooler on that improved the hot oil pressure a lot. It seems the Midget needed one and didn't get one, while the B didn't need one and got one.
Mike Howlett

The late model B's in the US market did put out less power, but they ran much hotter. They had about 1 quart less oil pan capacity, a hi temp thermostat and a catalytic converter, and ran with a retarded spark most of the time. Because they ran sohot they added an extra water line at the rear of the head and two electric fans. They had no oil cooler and worked just fine.

Prior to 1975, the oil cooler was typically only fitted to the US cars and was an option on the european cars that ran at high autobahn speeds.

The cooler was required because of lube failures from the additional friction heat generated by the 5 main bearing engine in 1966? By the early 1970's oils had improved and it was no longer an important issue. The engine I'm using in my '67 GT is based on a '79 crank and block rebuilt at 140,000 miles. The car was from Las Vegas Nevada. I rebuilt it with standard bearings. It didn't have an oil cooler before and it doesn't now.

Oils are way more better today than 1975. An oil cooler for a stock or lightly modified engine is just one more potential problem in my opinion.

I looked in the archives a while back and I couldn't find anyone complaining of main bearings failing because of oil overheating and causing a lube failure. In 1965 I had an Alfa Romeo that cruised at 5,000 rpm at 75 mph. I had the main bearings fail twice from lube failure. I got to know the bottom of that engine quite well. That wouldn't happen with today's oils.

my 2 bits


Barry Parkinson

Oil cooler good. Thermostat very good.

Don't "hot-tank" aluminum as it will not emerge!

Must be cleaned by alternate method... radiator shop can do it but they hate oil. Transmisison shop can do it as most auto trannys are aluminum (and lots of manuals).


Do note that most folks who swear by oil coolers live in hot climes. Places like Nevada regularly exceed 40 degrees, and you need all the cooling you can get. Driving a mellow 100km/h in a 25 degree ambient temperature, however, the oil will not overheat, guaranteed.

It is indeed true that the very cars that most needed the coolers (hot-running late US-spec vehicles in the insanely hot Western US) didn't get them - the cars are honestly pretty lousy on hot (>35C) days, but when summer is over - temperatures below about 30 - they do just fine. If you drive hard, you could get a cooler WITH a thermostat. If you drive gently, chances are your oil will seldom need any cooling.

I don't think oil coolers hurt. I went with the best high capacity oil pump I could find and the largest cooler i could use. Over kill? maybe, but the cost is low and the risk - unacceptable
Frank Baker


If it makes you feel better - good. Search the archives and try and find anyone that reports having lost a bottom end from lubrication failure because of failure to have an oil cooler.

The truth is a Toyota with a 210 f thermostat and 0-30 oil is far more demanding than a 95 hp MGB. The modern engine has tighter clearances and requires better oils than the loose MGB engine. The oil cooler looks cool and makes your car unique with an oil cooler. Only antique cars or race cars have them.

Do you need one? "I don't think oil coolers hurt".

Look at the archives for all the angst on how to change the oil in the oil cooler. - or how to keep the oil warm enough in the winter to evaporate the condensates out of the oil.

Your 1800 cc engine that puts out 98 horse power must be a real high performance engine to require an oil cooler. If you don't believe me just look. It came that way from the factory.

The engines needed oil coolers in 1966. They haven't needed them since 1973. Not because they were so high performance, but because they sold them here in the states without overdrive to keep the cost down. In Europe the majority of MGBs had overdrive to keep the rpms down. Oil coolers were stock in the USA, not Europe. By 1973 oil was good enough they didn't need an oil cooler even without an overdrive. Oils haven't gotten worse in the last 32 years.


Barry Parkinson

Down here an oil cooler makes sense(Arizona), when I lived in central colorado I had to "plug in my car every night just to be able to start it in winter.....everything is relative.
Still.... they do look so cool
J A Kelly


With regard to state of oil in oil cooler I can only think of is that a Mineral oils form waxes in icy cold weather and there is a permanent thickening of the oil especially with an exposed oil cooler, apart from general varnish and sludge issues.

Also with cold start ups (when most wear occurs) I would consider a synthetic as it has far superior flow providing the quickest way to protect engine.

Even at operating temperature even if a 20W50 stayed at required thickness, it runs hotter and is therefore in fact is likely to be thinner than a say a synthetic 0W40, so the thicker mineral oil offers less protection at operating temperatures as well as cold starts.


I follow the first bit, but I thought the idea of a multigrade is that it keeps the same viscosity across a temperature range?
Steve Postins

Nice to have so many views on this!

I use to drive my MGB about 3.000 miles annually, from april to november. I have used mineral 20W50 oil of decent quality. A lot of long runs, very little driving around town, and no real winter starts.

With that kind of driving, I really did not expect to find all that sludge in the oil cooler. Surely it must harm oil circulation? That is why I still wonder if the cooler is doing more harm than good.



>I thought the idea of a multigrade is that it keeps the same viscosity across a temperature range?

Not exactly. A multigrade oil is a lighter-weight oil that is artificially made to act as a heavier oil at higher temperatures. So a cold 20w50 flows like cold 20 wt oil (which is what it is), and at normal operating temperature is made (by way of additives) to flow like a 50 wt oil. But a cold 20 wt is still much thicker than a 50 wt at temp.

The primary cold-weather advantage of synthetics is that they tend to have a much lower pour point. The pour point is:
"5 degrees F above the point at which a chilled oil shows no
movement at the surface for 5 seconds when inclined. This measurement is
especially important for oils used in the winter. A borderline pumping
temperature is given by some manufacturers. This is the temperature at
which the oil will pump and maintain adequate oil pressure. This was not
given by a lot of the manufacturers, but seems to be about 20 degrees F
above the pour point. The lower the pour point the better. Pour point is
in degrees F."

Rob Edwards

Inclined at what angle?
Chris C

The website doesn't say....
Rob Edwards

Tore: I got the same kind of sludge from my oil cooler, I'm in North Carolina and we get hotter temperatures than you normally see. It took me about an hour to clean it using a parts washer. I removed my oil cooler for about 2 years and never noted any increased engine temperature. I think the oil pressure was a little higher at speed and perhaps a little lowe at idle speeds when the engine was hot. I know MG's competition for that era did not use oil coolers. TR-4, Sunbeam Alpine and I don't recal the Fiat 124 I owned having one. I wonder how many MG's were sold because some saleman told the customer "The MG has a racing oil cooler, other cars do not have one." The main objection I have about not using a cooler is that there is still one external oil hose that can fail, of course thats only half as many hoses as with the cooler. FWIW, Clifton
Clifton Gordon

BL stopped putting oil coolers in the cars due to cost, not engineering.
I live in Northern Nevada. -15C to 40C over the course of a year (although 40C is rare).
I've driven the 'ol girl in temps beyond that range (but not in comfort!).
Cooler, when I did the rebuild, didn't have squat for "sludge" in it. But I ran the heck out of it so the engine (and oil) definitely got hot.
Have recently installed an oil thermostat and have noticed mostly that it warms up quicker (but engine has been hotted up too).

Modern cars DO TOO have oil coolers. Most are hidden in a radiator end-tank.


All the coolers I have seen in the end of a modern car radiator tanks were transmission oil coolers. I have two modern cars and neither has an engine oil cooler but both have transmission oil coolers in the radiator. Clifton
Clifton Gordon

In extreme cold conditions you would be unable to start an engine with mineral oil but could with Synthetic. This applies to all cold starting situations to a degree, so using a mineral puts extra strain on starting system.

A mineral uses a light base oil which burns off easily and adds Viscosity Improvers to give the 50, but these breakdown, giving rise to the possibilties of crud being left behind in engine.

Synthetics naturally flow a low temperatures so a thicker base oil can be used with minimum Viscosity Improvers and therefore the engine will stay cleaner.


Steve to put some numbers on a multigrade
Viscosity at 75 F 212 F 302 F
10W-30 100...10..3

Synth oil:

0W-30 40...10..3

Since the synthetic oil thickens less on shutdown your startup will be easier and so will the stress on your engine. I will avoid 20W50 viscosity cold!


Something else learnt, thanks! I'm almost tempted to unluck the padlocks on my wallet and try some synthetic at the next change. Well, semi-synthetic at least.
Steve Postins

My 79B on hot days (about 80 deg. F)
had idle oil pressure of
40PSI without the oil cooler. When I put a
new oil cooler on, idle pressure was 50PSI+.
I think in really hot climates the oil cooler
would make you feel more comfortable with your
idle oil pressure, as Paul noted above.

The failure point with coolers is actually the
lines and fittings. If you install one, make sure
to get the reinforced cooler lines and make sure
the fittings are tight.

For 36 years I have people asking this question & you will hear it all as a responce. I have 3, 4 cyl gts. with 95 to 100 h.p. & 300k + on each + a 3500 gtv8 with 451K & a 4.2 with 250k (250 hp) & a 4.9 with every thing done to get 300 hp. out of her with 100k & not a oil coller on a one of them. I can run a 13 sec. 1/4 mile with the 4.2 or the 4.9. I use castrol 10-40 to 20-50 & I change it 3 to 6 tho. miles. I have a trailer hitch ON EVERY M.G. I OWN & I have pulled other Bs & gts cars back with my 4 cyl. from Ark., Fla., N.C., Tex.,RI.,. I use to go to mg car showes every weekend from 82 to 92 on the east coast with a 3,000lbs u-haul trailer behind my V-8 & I was stuck in 106 deg for 6 hrs. & it NEVER HAD A OIL COLLER. I sold rebuilt motors & mailed them all over the U.S. & Ca. & if it was not REAL HOT were I shipped them to I said not to run a oil cooler. So I am sure this will go on & on & I will go more miles with my M.G. & NEVER be slowed up with a oil cooler leak.
Glenn Towery

Use of an oil cooler can give benefits as both Ronald and Glenn note.

Cool oil lasts longer especially mineral (flow is key not pressure), however hot thin oil flows better and cools better. Matching the combination of oil temp and vis with your own requirements is the trick.

F1 use straight 5 or 10 weight oils although engines only need to last weekend.


Sludge build up in cooler will hinder flow, IMO disconnect cooler and take temp readings and then decide on whether a cooler WITH THERMOSTAT is necessary.



This thread was discussed between 03/01/2005 and 23/01/2005

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