The MGA With An Attitude
Engine OIL COOLER, Theory and Benefit - OF-105E

At 03:46 PM 3/11/2009 -0300, Dave McCann wrote:
>>"I was curious if you'd seen this information:
This guy has mounted the oil cooler below the radiator shelf".

I hadn't see that one before, but it is nothing unusual.

>>"I was wondering if you had any thoughts on how this position might work with the stock valance (i.e. no holes or ducts)".

The final position of the oil cooler is somewhat interesting in that it may take in preheated air from aft of the engine cooling radiator. This article makes no mention of any concern (or knowledge) about the oil temperature. I suspect that most people who buy and install an oil cooler are in the same boat, actually having no idea if the oil cooler is of any benefit at all.

>>"I'm about to put an oil cooler on a 1600 I picked up from George Kress last year and I'm trying to decide where to put it".

Last July (2008) I came very close to mounting my oil cooler below the air pan (still ahead of the radiator). I was fiddling with long bolt spacers to position the oil radiator low enough to allow use of the starting handle, ran into issues of hose length and routing, then ultimately ran out of time on a tight schedule. Since this was not an issue of keeping the car running or not, I put the oil cooler back on top where it has been for more than 20 years. Some day I may have another opportunity to fiddle with it some more.

If this guy had problems with it overheating at any time with sub-freezing ambient air temperature, he has (or had) some kind of problem that is far more significant than any of the things that are shown on that web page. To make it boil in cold weather you either have to stop almost all air flow through the radiator, or stop flow of coolant inside the engine. Having inadequate antifreeze solution and allowing the liquid to freeze can do that.

>>"Considering the amount of back flow (air flowing forward through the radiator) at idle the guy is describing, I'm wondering if a fair portion of his improved cooling is coming from the baffle he added to the hood".

That is quite likely. Closing the ports where hot air can backflow around the radiator is important and very significant in effect.

>>"I suppose mostly I'm trying to decide what the simplest mounting point might be. The driving I did in the car last year indicated that it was "cooling challenged", so I'd like to try to get it right quickly before the big Key West thing in 6 weeks or so. One other potentially complicating factor (i.e. maybe or maybe not) is the MGB radiator on this car".

A stock MGB radiator is identical in size and shape to a stock MGA radiator, mostly only different in mounting flanges. I believe that the original MGA cell core radiator may have been better at cooling than later tube type core units, but cell core radiators are relatively expensive and are particularly rare today.

Most cars will do quite well without an oil cooler for normal driving. The reason I installed an oil cooler on my MGA was because in 1989 I was about to take a long road trip towing a trailer at expressway speeds and through a lot of mountain hills. I also do substantial autocross competition involving periods of full throttle and high speed engine work interspersed with periods of engine off with no air flow. Under such conditions it may be observed that oil pressure can drop slightly, which is a result of lower viscosity of the oil when hot. For most competition use it is of greater concern that oil should not be so cold as to cause abnormally high viscosity and restriction of flow resulting low oil pressure.

In 1989, and still today, I am not absolutely certain that my oil cooler was ever necessary or would ever improve life of the engine. Under conditions that could promote abnormal heating of the oil, the oil temperature is not likely to rise much higher than the coolant temperature. The engine is after all water cooled, and the oil is much of the time in intimate contact with the engine block. Oil in the engine does pick up heat from splash on the underside of the pistons as it cools the pistons. It also dissipates heat by conduction through the oil pan to the outside air.

I can tell you that my oil cooler does work in a noticeable way. When putzing around at low speed in a club caravan (or stop and go traffic) on a hot day the idle speed oil pressure will drop noticeably, like 20-30 psi when I'm used to seeing 40 psi at idle. I can subsequently take a hard run at speed on the expressway with heavy throttle, perhaps even towing the trailer, and the result will then be 40 psi at idle. This tells me the oil cooler is reducing oil temperature when running hard on the highway, which is exactly why I installed it, so I think I will keep it in spite of never having measured the oil temperature.

When I was considering mounting the oil cooler below the air pan, I wasn't particularly concerned about air flow through the oil cooler. A small amount of oil cooling will drop oil operating temperature considerably. A small amount of air flow through the oil cooler will provide significant cooling effect. In fact if you could mount the oil cooler core flat to have vertical air flow with no forced air and no turbulence, then thermal convection alone would move enough air to provide significant oil cooling.

Any small amount of turbulence around the oil cooler will likely move significant flow air through the oil cooler. As such, I suppose that venting through the front valence panel is not needed (except for a no-holds-barred competition car). Advantage of direct venting for the oil cooler is that you can use a smaller oil cooler to achieve the same cooling effect. But before you worry about any of that you have to know the actual oil temperature and how much oil cooling you really need (if any).

An oil cooler will not lower engine operating temperature at all unless oil temperature is kept significantly lower than coolant temperature (which is very unlikely unless you have a very large oil cooler). Oil cooler in front of the radiator may preheat incoming air a little, but obstruction to air flow is likely insignificant. Total air flow space (in square inches) between fins and tubes of any radiator (oil or water) is always much less than air flow space ahead of aft of the radiator. If the oil radiator is placed an inch or more ahead of the water radiator, air flow can bypass around the oil radiator to reach the face of the water radiator. As such, air flow for the water radiator is not much restricted by the oil radiator, and the mix of cool bypass air with heated oil cooler air will result in combined air being substantially cooler than the oil cooler surface before the air reaches the water radiator.

The idea of an oil cooler in front of the water radiator restricting air flow through the water radiator is pretty much nil, or an old wife's tail, although preheating the air as it passes through the oil cooler may have some small effect. The negative effect of this preheating should be 100% offset by the fact that the oil cooler is removing the same amount of heat from the engine.

Considering "that guy's" picture through the MGA body front opening, the 4-inch air hoses would seem to be obstructing air flow to the water radiator. However, the same comment about cross section of air flow space applies here, that even with the large air hoses in that position the remaining air flow space is far larger than the cross section of flow space through the radiator.

For a lot of MGA, especially some wearing a somewhat restrictive aftermarket grille, the grille itself is more restrictive to flow than anything you would see between the grille and the radiator. Competition cars will often have the grille removed, or remove half of the slats in the grille to reduce restriction to air flow. There have been a number of innovative grille "eyebrows" used to improve air flow through the original grille.

You might install your oil cooler in any convenient location with very little affect one way or the other on engine cooling. Practical application of the oil cooler is to lower oil temperature, not to cool the engine.

There is one key question that you didn't ask. Does the oil cooler do anything useful and is it worth the bother and expense of installation? Most people I know who have an oil cooler installed have done so on the basis of a rash assumption to that answer.

No one yet has ever convinced me that any oil cooler installation in an MG street car is proven to have any beneficial effect on engine life or engine operation (including my own installation). There is some implication that the MG factory had an idea that the oil cooler must have some benefit, otherwise they wouldn't have taken the expense to make it standard equipment on so many production cars. As for my own oil cooler, I am willing to admit that it is largely supposition and/or superstition that causes me to retain the installation in spite of some inconvenience in servicing the car. Maybe it falls under the idea that it does no harm, and it may have some beneficial effect, so why not? That sort of thinking can cause lots of people to spend lots of money for no particular benefit, but the parts suppliers love it.

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