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MG MGB Technical - How much cooling does an Oil Cooler provide?

I really need to ask this question on the V8 board, but as there seems to be much more activity on this board with many knowledgeable folk participating, I am asking it here.

When I built my MGB GTV8 I didn't fit an oil cooler, my rationale being that the RV8 doesn't have one, so therefore it can't be necessary. I'm pretty sure that in the UK at least the 1800 MGB doesn't need one either.

On a continental tour in 2015, the old V8 did get very hot when stuck in traffic with the outside shade temp at 36 C. The temperature part of the dual gauge climbed into the oil pressure half of the dial and reached about 2 o'clock on the dial face. Not that the engine misbehaved in any way. The oil pressure kept up at it's usual 35 psi and the idling with fuel injection was steady.

My question is this. If I did fit an oil cooler, could I expect it to make a significant difference to the water temperature? The car's engine temperature is always OK providing it can keep above 40 mph and since the oil cooler on the V8 has no forced ventilation, being underneath the area of the fans, I doubt a cooler would help much. But what do you think?
Mike Howlett

Don't think it will benefit the water temp at all, fit one by all means but put a thermostat on it to keep the temp UP.
David k Brenchley

Mike - Several years ago the oil cooler started leaking. Since we live in the Puget Sound area of Washington State (near Seattle), I just removed the cooler and rerouted the external line on the engine. To date I have not experienced any ill effects. Cheers - Dave
DW DuBois

Mike, the bottom end of the engine, particularly the main bearing caps are a little suspect as the temperature rises. The locations are small "steps"and the caps are Cast Iron with a different rate of expansion to the block. The bottom end is known to flex as well. As temp rises the caps can begin "fretting", in other words moving! This fretting causes the location to be lost and the block is then scrap. Oil is the major cooling agent at that end of the block. Even circulating the oil to an external heat exchanger at ambient temperature, will cool it and remember the pumps are high flow units. This fretting and block flexing was why the later 4.0litres (actually still the same capacity as the 3.9's) where fitted with aluminium caps which were later cross bolted to further stabilise the block and caps. Personally I would't run a Rover V8 without a 13 row cooler.
Allan Reeling

I thought it was the exhaust routing through the inner wings that kept the RV8 cooler than the BGT V8.
s p brown

That's interesting Allan. I have read about the cross bolting of later V8 engines but didn't know the reason for it. Maybe I will get an oil cooler after all.

S P Brown in West Yorkshire, was it you that I bought the rusty GT from way back in 2003? If so, that is the car that is now my V8. As for the exhausts, I have the RV8-style through the wings manifolds, and they are wrapped in insulation so that more of the heat is passed out of the engine bay.
Mike Howlett

There is a huge benefit for V8s by fitting an air-dam that scoops air into the lower part of the rad (and the oil cooler on RB cars), but even moving the number plate from in front of the slots of the standard valance to the front of the bumper makes a significant difference. There should be an fibre-board air-duct between the slots and the front of the cooler which also adds to the forced ventilation. Mine tended to be rounded rather than rectangular which let a lot of air escape, so I fitted a metal bracket round it to force it into the correct shape.

I think oil coolers on the 4-cylinder cars especially in the UK were more to assuage customer concerns about seasonal changes in oil pressure than anything else.

They may be more beneficial on V8s with twice as many cylinders in the same engine bay space, and not much difference in the radiator size. V8s have twin cooling fans which whilst not being very efficient are pushing more air through the rad at idle than a mechanical would, air which will also be passing through the upper-mounted cooler on CB cars. But on RB cars the only air-flow through the lower mounted cooler comes from forward movement, so none stationary at idle, and one can expect to see a marked reduction in oil pressure over time in warm UK weather, let alone hot.

Maintaining 35psi in a factory V8 would be a miracle. With a max of 42psi, immediately coming to an idle I probably get 20-25, but that will steadily drop over time to 10 or less. As Roger Parker has said when asked what the hot idle pressure should be - "What hot idle pressure?"

I did get some concerns over V8 cooling from the temperature gauge at one time - not as bad as yours but well into the red zone and again not affecting the engine or causing coolant loss, and when the rad needed replacement fitted a 30% uprated one. However that 30% represented four rows of tubes instead of three, and after the air had been past three rows it picked up precious little more heat from the fourth, so the improvement was marginal. The biggest improvement by far came from adding local earths to each fan i.e. keeping the existing earth wire as well which feeds all the front lighting, and connecting the spare output spade on the alt directly to the 12v terminal on the fan relay, again in addition to the existing 12v feed, so acting like a ring-main and halving volt-drop under high currents. Since then cooling has never been of any concern, staying well below the red zone, even stuck in traffic in the hottest weather.


Thanks for your detailed reply Paul. To address your points. Although my conversion is an earlier shell (1969) I have fitted the later valance with the two cooling vents in it, and I have moved the number plate to the front of the bumper. Originally I did have a "Special Tuning" fibreglass valance with an air dam, but the thing kept cracking, and it got knocked on high kerbs, so I got rid of it and went back to the standard ventilated item. I have fabricated an aluminium bottom plate to channel the air into the radiator rather than escaping under the car.

I'm undecided about mounting the cooler above or below the radiator duct. On the one hand I don't want to obstruct the air flow to the water radiator, but I do see your point about there being no air flow over the cooler when stationery. However, as Allan pointed out, even without air flow, the oil at 90C is going to lose heat to the air even when the ambient is 35C. Not sure what to do.

As for oil pressure, mine is never as low as 25 psi, and never higher than 40. I remember Roger Parker writing about his experiences with police Range Rovers that showed no measurable oil pressure while idling hot. My engine has the standard pump and relief valve from the 1991 Range Rover that the engine came from.

The electrical system on my car is an Auto-Advance (or is it Advance-Auto?) wiring loom from the USA and the cabling is substantially thicker than MG's standard wiring, the earthing is comprehensive, and multiple relays are used. I have no worries on that front.

So the question is, above or below the duct? Answers on a postcard please.
Mike Howlett

While the radiator performs the function of cooling both the cylinder head and the cylinders, it should be noted that it is actually the oil that cools the internal parts of the engine. The average petroleum-based oil begins to break down at approximately 2720 Fahrenheit (1330 Celsius), while the average synthetic oil begins to break down at approximately 2820 Fahrenheit (1390 Celsius), and oil can only become thicker by becoming overheated and vaporizing its lighter components. In fact, at a sustained temperature of 3020 Fahrenheit (1500 Celsius) for one hour, an API-quality oil can lose as much as 15% of its volume. As motor oil degrades with use, it becomes less thermally efficient and thus cannot remove heat as well as it did when it was new. The coolant cooling system of a hard-pushed engine can keep the coolant temperature within a normal range until the oil temperature has increased to such an extent that the coolant temperature will seem to rise unexpectedly for no apparent reason (unexpected unless, of course, you have installed an oil temperature gauge). The reason for this is that the oil has become so hot that the radiator has reached the limit of its cooling capacity. An oil cooler helps to get rid of the excess heat that can destroy the additives that were added by the refiner in order to help protect the engine. Thus we understand that the crucial deciding factor behind installing an oil cooler is the fact that it is the oil that carries away the heat from the moving parts. How much heat is carried away by the oil? As an example, the US Army’s Armored School Handbook states "The engine depends upon its lubricating oil to carry away at least thirty-five percent (35%) of the heat created, hence, the oil circulating system of this engine has a very important part to play in cooling the engine". Obviously, the BMC B-Series engine of the MGB does not undergo the strain that the engine of an armored fighting vehicle does, but this serves to prove that the oil does indeed perform a significant function in the cooling of the engine. This being the case, a thermostatically-controlled oil cooler can be considered to be a wise move for a car that is going to be kept and run for many years.

By means of the use of the oil hoses (flexible pipes) and the 10-row oil cooler from the 1974½ -1980 model MGBs (BMC Part #ARH 185, Moss Motors Part # 235-990), it is possible to relocate the oil cooler to a new position behind the front valance in order to permit an unobstructed airflow into the matrix of the coolant radiator, while mounting the vented front valance (BMC Part # HZA 4812) from the 1972 to 1974½ models along with a venting duct to the oil cooler that will, in turn, provide adequate airflow to the relocated oil cooler. The heated air will escape better if it exits under the car as opposed to through the coolant radiator and then through the engine compartment. As an additional benefit, this vented front valance was originally introduced as an aerodynamic improvement in order to reduce the tendency of the front of the car to 'lift' at high speeds. Moss Motors here in the USA can supply this later Chrome Bumper front valance with its two front vent holes (Moss Motors Part # 457-115) for $199.95. Victoria British can also supply it (Victoria British Part # 9-918) for $189.95. Our British cousins can get it direct from the manufacturer, British Motor Heritage (British Motor Heritage Part # HZA592), which can supply this later Chrome Bumper front valance with its two vent holes for £94.73. When installing, hook up the hoses (flexible pipes) to the oil cooler while it is hanging loose under the car, and then bolt on the oil cooler with its four mounting bolts.
Stephen Strange

Stephen, this is why I posted my V8 enquiry here, so I could get feedback like yours, Allan's and Paul's. Thank you for your comprehensive explanation. Yesterday I ordered a 13 row cooler and the pipes to mount it under the radiator duct (BHH1612 and BHH1613 for the V8). I already have the vented front valence on my car, and the reg. plate is mounted higher up on the front face of the bumper so it doesn't obstruct the vents. I should have it all kitted up ready for summer. Thanks all.
Mike Howlett

All good, every v8 conversion I have done has had an oil cooler so I can't really comment on one without but to me it sounds like you have a cooling system problem if you have to be over 40 mph to keep the temp down

If normal air flow will keep it cool above 40mph there must be a problem with the efficiency of your cooling fan(s)at lower speed- Might pay to check that the fans are blowing wind in the rearward direction
William Revit

No Willy the fans work well and are blowing in the right direction! In fact you can feel the heat coming out from under the wheel arches when they are on. There is so little space around the V8 in the MGB engine bay that it is hard for the hot air to escape, even though I have RV8-type headers. Added to this is the barely adequate radiator size.

Maybe I have the fan thermostat set too low. My water temp gauge is calibrated in degrees F and is plugged in below the water thermostat in the head. I have the fans come on at a reading of about 190F, but by then the temp increase will continue until the gauge reads about 210F when the fans start to make a difference. It's never going to boil because of the 15 lb cap and the 4-Life coolant which they claim doesn't boil until 180C or 356F. (

Does anyone know anything about 4-Life coolant? I begin to wonder if it's heat transfer properties are as good as conventional water/glycol mixtures. I can't find any info on it on the web.
Mike Howlett

"Originally I did have a "Special Tuning" fibreglass valance with an air dam, but the thing kept cracking, and it got knocked on high kerbs"

BT, DT more than once :o)

Incidentally when I'd done the cooling fan mods it was during a period when the ambient temperature was 30C. I shut the car in the garage (exhaust piped outside) running at a fast idle (throttle wedged, not choke). It got up to 41C in there, but the temp gauge didn't get more than 2/3rds the way from N to H.

One thing I did notice when peering under the car was the heat haze. With the bonnet shut apart from a small amount of air flow that can escape down the tunnel, the majority of the air that is blown through the radiator has to escape downwards. Much of this does come out from under the wings, but there was a significant amount that was coming forwards and being drawn up by the fans and recycled through the radiator!

I've seen this effect stopped in traffic with a following breeze at the end of a classic car run at Brighton when we were being interviewed. People were beginning to panic, and they had to curtail the interviews.

Put the cooler behind the grill and in front of the two fans - I have run this arrangement on my V8 for 20+ years and I never see other than 40 psi on the gauge. idling, running, hot, cold, whatever.
Chris at Octarine Services

Paul - check ! Several miles of jam in S. London at 41C. Oil pressure at idle 10psi. Fans running continuously. Temp guage 2/3 its range and well short of max. The fuel-injected 3.9 with blockhuggers did not miss a beat. The sole casualty was the leather back to the drivers seat which could not cope with my discomfort !
Stephen - the luboil is indeed the primary coolant for this engine and regular oil change is the key to long life but the lube system depends on proper circulation rather than constant high pressure. 10psi at idle doesn't harm this very robust Buic design so long as the pressure leaps back to 40 when the light turn green !
Mike - the factory fit was right from the start - (can't remember what Costello did)- it can't be wrong to copy.
And for those who haven't driven a B V8, this is still the best car that MG ever made by a very long chalk !
Roger Walker

"Mike - the factory fit was right from the start"
Yes it was on the BGTV8, but the RV8, which has an identical engine to my conversion, has no oil cooler. Why not? I have never had any oil pressure worries, even when the engine is very hot. However, I am going to fit an oil cooler.
Mike Howlett

Mike, maybe it has something to do with a difference in the airflow over the sump in the RV8 which provides most of the oil cooling.

Never worked on an RV8 - is the sump the same as the 3.5 litre used in the original BGT V8?
Chris at Octarine Services

Agree with Chris
Mount the cooler as far forward as possible so that air can still get around it to all the radiator surface
This photo shows where I believe is the best place to mount them
The cooler needs to be off to the side like this to clear the bonnet safety catch and the support post
Sorry I don't have a closer / clearer pic

William Revit

I think the factory engineers thought they had cracked the heat problem in the RV8 by putting the exhaust out through the inner wings. I am sure Willy's arrangement with the luboil rad immediately in front of the main water rad will work but it is sitting where the factory fans should be. A single electric rad fan will do the job but it won't give you any redundancy when it fails. Without a fan you are stuffed!
Roger Walker

With reference to Mikes post on 03/02/17,you mentioned about the police Range Rovers, running with no readable oil pressure when hot, I spent most of my working life working on these, and we never had any with oil related problems, we had a great deal overheating which caused warped heads and blocks, head gaskets, some of these had 110v generators on running off the crank pulley and would sit for hours running at between 2000rpm and 3000rpm and they would always lose the coolant due to one of the above, before they had oil pressure issues' there is no comparison between how these vehicles were used and how people drive there V8 Bs we had one once do 165000 miles in 15 months and another that I put 3 clutches in, in 5 days, and on the Monday of the next week put a crank in, as the original had snapped,
Andy Tilney

If you have a good look at the pic.--
The bonnet slam panel is an original V8 item with the holes for mounting the electric fans down behind the cooler and in front of the radiator-There's plenty of room there for everything-
However on this particular car it didn't get electric fans, I mounted the radiator as far forward as possible and used a viscous coupling fan driven straight off the front of the crank---worked faultlessly
I've gone off electric fans since
William Revit

This thread was discussed between 02/02/2017 and 06/02/2017

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