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E39_M52b25 Engine Oil Cooler Final Setup

With the entire engine tuning modifications the inevitable core/oil heat would build up in the engine, simply because there is more horsepower to cool down. You can read about what I have altered and change within the engine with other pictures.

When the core heat in the engine rises the heat in the engine compartment rises to, and that leads to amongst other things a warmer intake manifold, ergo, that translates to warmer air when it reaches the head intake itself. Cold air is more dense, therefore we can add more fuel and add a good tuning to the mixture that will hopefully translates to more horsepower and who douse not need more power.


The modifications where relatively simple and straightforward and not that complicated (until it exploded in my face:-(). I bought the 13 row oil cooler from a seller on eBay. The hoses had to be shortened a bit to be fitted snugly. Two holes had to be made in the bracket that hold the water radiator for the new oil hoses. The oil cap was bought separately from another seller.


You should be on your toes when choosing the oil cap, sins there are some caps for sale, that are missing a vital part that goes into the hole at the bottom of the oil filter housing/canister. If this hole at the bottom is not closed the engine will not reach a full oil pressure. This hole at the bottom can have two purposes, one is; when you take of the original cap the oil is drained through that hole to prevent oil spill and the other is in some cases, if you have a pin with two rubber seals the middle pin is hollow and has the capability to bypass oil through it and come out at the top of the inside of the cap to prevent an over pressure. As far as I know, then none of these aftermarket caps have the mesh, that goes inside the filter itself and some of the caps, use the inside part of the original cap in conjunction with the aftermarket one.


:!: If you shorten the hoses, remember to keep as much constant inward pressure on the hose as you possibly can, while tightening the nut it self. Still,  I'm not 100% secure with this setup and need to find a good solution to prevent the hoses to come loos under pressure.

Word of warning, these fittings are not so safe if you do not take time and care :!:



My issues with the fresh intake-air heat in the intake manifold and the engine was, that it reached 62° - 70°c /144° - 158°f air temp. measured inside the manifold, at standstill and idling, with outside temperature at 20°c/68°f. To tackle this heat buildup I had two simple choices. Ether more cold air from the outside or external oil cooler. I opted for both solutions and the results where that the core heat (mostly the heat of the oil) of the engine dropped  from 103°c to 93°c/217°f to199°f, ruffly10% lower and air temp inside the manifold from 62°c. down to 43°c./144°f down to 109°f., or 31%. Now, that might not seem a lot, but then this is measured at standstill and idling. When driving the numbers get much better.


Sins writing this in September 2021 I have deleted the heat that goes into the throttle housing, with even better results regarding the manifold heat, just by deleting the throttle body heater.  After the delete/bypass of the throttle body heater the intake temperature fell drastically down  from 43°c./109°f  down to 24°c/76°f at standstill and idling with outside temp. at 12°c/54°f, that is an additional heat reduction of approximately 44%. without taking intro consideration the difference in the ambient temperature. This heat reduction, gives me much more elbow room to tune the A/F ratio and timing. you can read more throttle body heat wit other picture. All in all, heat reduction inside the manifold from 62° - 70°c /144° - 158°f  down to 24°c/76°f  that is a reduction of 61 - 65% :wub:from the start, with all the modifications regarding manifold temperature reduction.

Summa summarium; Engine heat doped down by 10%,  Air inside the manifold doped by  61 - 65% all measured at standstill and idling.


The original air intake plastic tunnel took the intake air all the way in front of the water radiator from the left middle of the front bracket and actually, partly sucking air from the inside of the engine compartment, where there is a lot of thin warm air.  As you can see, I cut the intake "spout" over, to enable more cold air to flow more freely to the engine intake, in conjunction with an air filter box that has an additional intake from the inner side of the wing that leads to the wheel well.


I am pleased with these results for now, although I'm dabbling with the idea of a larger oil cooler (no, there is no need for larger cooler). Now I can continue with the fine tuning of the partial bin. files, sins all the parameters have changed due to overall, a cooler engine and colder air intake.

After the installation I opted for painting the cooler in mat black heat resistant paint.

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My 523i Conversions and Maintenance

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