Using E36/M42 rads on M20? Edit - M20 expansion tank height?

[Brian28]

We've converted a couple of 4 pots to M20 2.5 for race cars and fitted the E36 328 rads for convenience (the type with expansion tank alongside the rad similar to M40/M42 but a bigger/deeper rad) as don't have anywhere on the shells to mount the M20 type expansion tank.

Had overheating problems yesterday at Brands, not sure if it was down to the rads or not. Both cars were fine on the road, but very hot on track. Anybody else used these on track and were they Ok? If not the rads, need to start looking for other problems. Thanks.

[DanThe]

Do you still have the oil coolers fitted? Makes a big difference on track

[Brian28]

Thanks Dan. Set up pretty much the same as we used to do the 320s in PBMW. Oil coolers fitted, thermostat inner gubbins removed leaving the outer ring in place, rear bonnet line raised slightly with rubber seal/trims removed, decent oil (Valvoline 20/50 race oil). Temps towards (and into) the red after 10/12 laps. The symptoms are what I would expect with a partially stuffed up rad (fine on road and only heating when under pressure at constant hight revs) but the rads were new and logically should have similar surface area/water capacity as the standard M20 ones, so I'm stuck for ideas.

Edit - Running with the heaters on full to try and help a bit

[DanThe]

I would get the rad swapped in that case.
I started out with an E36 aircon rad on my M52 track car and it would get too hot after a while, now changed to an S50 rad/separate header and oil cooler and the fan doesnt even come on anymore.

[Brian28]

Thanks Dan. Do you now offhand if the E30 header will work with the E36 M3 rad? I found a diagram online and it looks like the extra pipework on the E36 expansion tank is only for the cannister. Cheers.

[DanThe]

Pretty much any header tank will work, but yeah if you use the E30 its easier. You will need a different top hose too. The S50 rad is very similar in size to the E30 tropical spec rad which is another option. The core is much thicker which makes all the difference, I find my road car with M52 rad gets hot very quickly when stationary/slow traffic, no viscous either which doesnt help

[HairyScreech]

Strange, i would have expected the 328 rad to be more than man enough considering its normal application.

Is the core the same dimensions?
Is the tubing of the rad a different shape to the m20 rad?

[mrLEE30]

IIRC the tropical rad is not thicker, its just bigger (ie. goes further down toward the floor) its still a two core rad and its the same width.

for info all my E30's have run over here in 50C plus heat with Ac running with no issues, even in traffic.

you could also try some water wetter perhaps but i think a bigger rad will help

[DanThe]

IIRC the tropical rad is not thicker, its just bigger (ie. goes further down toward the floor) its still a two core rad and its the same width.

for info all my E30's have run over here in 50C plus heat with Ac running with no issues, even in traffic.

you could also try some water wetter perhaps but i think a bigger rad will help

Yeah but if your viscous stopped working you would know about it! Most race/track cars have the viscous removed. An elec fan in front of the radiator can also work against cooling as it blocks off some air flow

[Brian28]

Thanks for the input all. Chances are these would be absolutely fine tootling around the highways in Bahrain as well, but wouldn't do five minutes on track there.

I don't have an M20 rad for comparison but thought that the 328 would have been similar in surface area, but perhaps not. May well be less water capacity as well. Most likely plan of attack now is to use the standard M20 expansion tank with M20 aircon rad and see how it goes.

[Jhonno]

Have you tried a new oil cooler.. They are a service item like a rad also!

Also, raising the rear of the bonnet, doesn't work.. It is a high pressure area iirc, so will just force air back down into the engine bay.

[Brian28]

Another thought I had. Two of the front water pipes have a curve that sits above the level of the top of the radiator, so a possible spot for air locks causing poor circulation. The radiator top is the same height as the standard M20 rad. Does the standard M20 expansion tank sit higher on the bulkhead than the M20 radiator height? Wondering if it makes a difference having the expansion tank side by side, as the M40/M42 that use this type of rad both have lower water pipes that don't come above rad height.

[Jhonno]

Water pump new?

Good new coolant mix?

There is no reason a standard spec M20 should be cooking on track like that imo..

Have you got an oil temp gauge?

[HairyScreech]

You might be right with the air locks issue, the header tank does sit above the radiator height on the m20, even with the facelift tank.

[Brian28]

Thanks chaps. New water pumps and coolant mix on both cars, no oil temp guage. I'm thinking rad set up as both cars behave the same so would be odd to have a similar fault on both cars, the rads are the common element. Like you said Jhonno no reason really why they should overheat, the rads are the same area as the M20 ones (reading Nickphine 328 build thread) so the expansion tank height may be the issue. Building an engine for mine this week (the engine in it was bought from a breaker on here as a stop gap until I got mine built), when it goes in will likely revert to the M20 set up and weld on brackets/tabs or whatever is needed to position the expansion tank.