Cooling System Rule Clarification


First post on here, so hello! My brother and I are building up what will be our first “Spec” racer, and coming from more unlimited time attack car builds, I am having to get used to what I “may”, “shall” and “must” do.
So the question: I am fabbing up a dual pass radiator and am wondering if I have to retain the oem configuration for the cooling hoses? I noticed most use some combination of the early or late factory hoses depending on what single, double, or triple pass radiator is being used. I’d like to put both the radiator inlet and outlet on the drivers side and eliminate the tube that crosses the front of the engine all together (I have a later car).
My second question: Overflow catch cans are a must but do I have to use the factory expansion/fill tank? I’m going to guess this is a “if it doesn’t say I can change it, than I can’t” thing but on my other cars I’ve used a swirl pot expansion tank with a fill cap in that location and it made bleeding and air in the system a non-issue. Something I’d like to do in the e30 if I can.
Thanks in advance, really looking forward to getting this car out and running with you guys.


The final word on all of this is Shawn’s, not mine. Also, you should discuss these issues with your regional class director and get their take on things. The paragraphs below are good for SE region. Outside of the SE, if you tell someone that “Well, Scott Gress said that…” they’ll just wearily roll their eyes at you.

You can mix and match early and late cooling hoses to make the outlet config of your radiator work. The weakness of late cooling is the tube across the front is a little inelegant. The weakness of early cooling is the alternator can hit the rad return hose.

Note that early and late use different pumps. Early pump has outlet for reservoir. Late pump has fastening point for steel tube. With a little cleverness those can be mixed and matched too.

As you prob know, early and late use different reservoir’s and different hoses to link the reservoir with system. With a little cleverness, as above.

All that’s cosmetic BS tho. IMO what’s important is eliminating what hoses you can, and installing a pressure switch to a huge light on your dash. The hose from the back of the head can go, as can the ones associated with throttle body warming. The pressure switch is a big deal because we lose engines each year needlessly because of unnoticed coolant leaks.

The factory reservoir (expansion tank) needs to be in place. You’ll note that the CCR doesn’t have a paragraph that allows it’s removal, therefore you can’t remove it. It does not, however, necessarily have to be functional. If your heart is set on an alternative to the factory reservoir, I think you’ll be good, as long as the factory reservoir is also in place.

For a while I didn’t use a reservoir at all. I had it in place, I just didn’t any hoses connected to it.

Bleeding the system is a non-issue if you drill a tiny hole at the top of your thermostat. Then you can bleed the system w/o having to wait for the engine to heat up. Very convenient.


Allowance for dual pass pretty much guarantees crazy hoses. I have a fancy overflow tank that came with my car. I put a Vitamin Water bottle on Dad’s car. Powerade and Gatorade bottles work too, just don’t use the yellow Gatorade because it’s gross.


I will give the ole Keep It Simple Stupid side of this argument. The OEM BMW cooling system is more than adequate at keeping a SpecE30 cool even without the OEM clutch fan. I will agree with Scott about installing a low water pressure switch and protecting that radiator hose near the alternator on early model cooling systems as I was one of the victims of the hose being slashed and not noticing it quick enough to save the motor from damage.


I appreciate the responses, nice to hear what’s working and breaking from the guys out in the field already.
Scott- Thanks for the info on the parts interchangeabilities and week spots. Sounds like I should have no problem making something work with the oem stuff and my radiator. Trying one of the new afco lightweight radiators :). I like the idea of a low pressure switch.
Brian- Agreed about the yellow gatorade. I like using the water-wetter bottles for overflows, course that stuff’s pretty gross too.
King Tut-Definitely, regarding the KISS and how it works well in racecars. Although I’m German, so I like spending a bunch of time up front over engineering and building it to be as simple as possible, so when I’m at the track I get to enjoy it working overly well, reliably, and being easily to service. Probably not at all that necessary, but I enjoy it nonetheless.

I forgot to mention we are also building the car to hopefully run 25 hours of Thunderhill in a couple years as well.


Having run my SE30 in the 25 hr race, I can tell you this much…The E30 is at a big disadvantage in it’s stock form. Now, with a few changes, it can be a mild threat.

Feel free to hit me up for more on this. I don’t want to take away from the topic, which looks to be pretty much covered. I will only add this…it looks like you are over thinking this and would suggest you simply make sure it is functional, not overly stout.


If you need a new radiator for the late cooling system I would suggest the Mishimoto e36 radiator. My street car now has one since a water pump bearing failure caused the mechanical fan to cut a ring into the back of the factory Behr radiator. The Mishimoto has fully welded aluminum ends where the oem radiator can leak around the crimped on plastic ends. Also if you retain the heater core you should replace it with a brand new unit or the end caps will most likely blow out.


Fooshe- Message sent.

Turbo329is- yep, I have previous experience with the mishimoto radiators and am a fan, good bolt in quality for the price. I have a c&r racing radiator in my other car I like as well, although the application specific ones are $$$. I’ll be welding up a universal afco for the e30 and seeing how that works.
Thanks for the tip on the heater core, that’ll be something to put on the list of things to look at.


reply just sent.
Sorry for the delay


Here is another KISS suggestion. Double pass, both on passenger’s side. “e” top hose, “i” bottom arrangement so so everything is OEM, and away from the alternator pulley. Drill a 3/16" hole in the top of a 176 degree thermostat and use the OEM overflow tank. Route the overflow hose to a catch can and basically forget about cooling, except for the water pressure switch. Be sure to use a rust inhibitor in addition to water wetter as the cooling system will rust in a couple of days without it. Good luck!