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MG MGB GT V8 Factory Originals Technical - Oil Temp Gauge

Advice please. Standard Rover V8 conversion. Thinking about fitting a Oil temp gauge. What is best position for sensible readings? Sump? Or do these in-line sensor housings work, think they are made by Mocal/Aeroquip. If so whats best fit position please? Thanks Richard
Richard Evans

When I built my BV8, I had a second oil drain plug fitted into the sump (because I thought my exhaust was going to obscure the original drain plug). I used it to house the oil temp sender unit. Works great - Autometer brand.
Martyn Harvey


What a gauge, any gauge, is monitoring is not as important as your understanding of what it is telling you. Once your engine has warmed up and reached stable operating temperatures, there will be a range of temperatures in various parts of the engine. You can't monitor them all, so you have to rely on the temperature at a given point to provide a relative indication of the temperature at other points. The sump is a good place to do this, as all the oil will pass through there sooner or later. As a result, the sump temperature will be a representative "average" of the temperature throughout the engine.

Trying to determine what the temperatue should be in the sump is a bit beyond most of us, but we can take comfort in knowing that the manufacturer has designed the oiling system to be adequate for most usage. The important thing for us to be concerned with is any deviation from the norm. After you've installed the gauge, monitor it until you can establish "normal" values under various conditions. From that point on, if you see the temperature change under any condition, you will know that something is wrong, and needs your attention.

Having said that, it would be nice if you, Harvey, and others with an oil temperature gauge would report back to the list with your "normal" values. That would help others to evaluate a new engine installation early on, to eliminate any overheating problem before it does any damage.
Dan Masters

My old roadster had an oil temp gauge & I had a boss welded in the side of the oil pan, low & to the rear of the sump. Oil temps ran about the same as the water temp.

When I built my GT with a 4.2, I found it was a much hotter running engine than the 215. As it was already installed, I did not want to drop the oil pan to install a bung, so I found a spot on the oil pump base that I could drill & tap for a sender. Oil temp runs 10-20' hotter than the water temp now that I have added an oil cooler, but before, it was running 250-270'
Jim Stuart

I concur with Jim, oil temp is about the same as water temp. I don't run an oil cooler and usually (summer) the temperature range is 180 - 210.
Martyn Harvey

I am not at all sure that the oil temp is the same as the water temp and anyway it seems that the temperatures mean quite different things. (On my Landrover, the two temp guages produce quite different readings.)

An excellent article by Shepherd in his book The Vehicle Dependent Expedition Guide - I don't have all the publication details to hand but you can probably find it on Amazon, - describes in great detail oil, how it works, what it does etc and all of the different types and identification codes and what is best for which kind of situation. It is sometime since I read the article but he writes also about the correct positioning of the temperature sender which Shepherd says is the sump and also goes on to say that although oil will last a long time, it is the various additives (he describes them and what they each do) which wear out and this is a big reason why oil needs to be replaced regularly. He also goes on to say that some of the additives only starts working at 70 degrees and that the oil loses its effectiveness at (I think) 120 degrees and that if at any time your oil reaches this temperature then you should stop the engine immediately. (I think that you can take it that if anyone's water temp gets to this level, the car will have stopped itself some considerable time earlier.)
Anyway, I think that this book and at least this article is very well worth reading and if people are going to start monitoring oil temperature then they might as well understand how to do it and what it all means.

Under way I wouldn't be surprised to see the temp gauges show much the same thing, but left idling for a long time in hot weather I would expect the oil temp to go up whereas the water temp would be controlled by the cooling fans. I can see the effect of this on my oil pressure gauge. More gauges is more things to worry about. Why do we need tachometers, oil pressure and water temp gauges for road use anyway? The only time I have had a hose fail while under way it was a slight missfire under acceleration as water sprayed on the plugs that told me, the gauges showed completely normal even over the several miles it took me to get to the next services. Now pressure, temp and level *alarms* are a different thing, I would have stopped immediately if I had known I was losing water.
Paul Hunt

This thread was discussed between 12/10/2002 and 14/10/2002

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