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Cooling your m30

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    Cooling your m30

    Just wanted to throw this out there for all you m30 swap guys. I know we're coming towards the end of summer heat waves but hopfeully this will be of use so some people.

    Cooling the m30 is always an issue. Deleting the stock mechanical fan means there is ZERO airflow over the radiator when doing anything less than 10mph. So in stop-and-go traffic, you'll be overheating within minutes. One possible solution is to rig up and auxilliary switch for your aux fan so you can flip it on either low or high when things start to heat up. This works great but can be a pain in the ass to turn it on every time you come to a stop light, then turn it off when you get up to speed. So I started looking in to other solutions.

    First off you'll need a lower-temp aux fan switch. All e30s, e28s, e34s, etc. came with 90C/92C switches that turn the aux fan to low at 90 and high at 92. The problem is that the OEM thermostat for an m30 is 78C! Which means you'll be getting pretty hot by the time that thing kicks on. So, after some searching I lcoated this p/n


    It's an 80C/88C switch from the e36 318ti. Switch it out, throw in a bottle of WaterWetter and you'll probably be OK for most days under 90F.

    But for those of you running a/c like I am, that stock aux fan is not enough to cool the rad and condensor, even on high. The air picks up too much heat when moving over the condensor, and therefor cannot remove enough heat from the radiator. And even if you aren't running a/c the stock aux fan sits about 1.5" away from the radiator, which kind of acts like a big wall when it comes to airflow. It's much easier for air to go above, below or around the rad than it is for it to pass through it. I'd bet only 10-20% of the air coming off the fan makes it through the rad to actually remove heat.

    The solution is, of course, a better fan. I settled on a Spal 16" curved-blade pusher.

    It fits perfectly in the stock aux fan location and is cake to install. It also pushes over 2000cfm, more than double what the stock fan does.
    Note: If you're not running the stock a/c condensor, you really want this think sitting ON the rad, not 1-2" away from it. So either re-do the mounting mechanism so it sits closer, or check this out: It might work but I haven't personally tried it.

    e30 aux fans are 2 speed; high and low. You'll want your new fan to be high/low too to match your fancy new switch. You can do this by either removing the resistor from your stock aux fan and attaching it to your new fan, or with an aftermarket resistor. Spal used to make one that I bought back in 2010, but now it seems to have been discontinued. Any aftermarket resistor should work as long as it's good up to 30amps.

    Now you've got a nice, big fan that'll cool your car no matter what. It'll come on automatically, shut off automatically, and make your drives much more enjoyable with no fear of overheating!

    Last edited by CorvallisBMW; 03-13-2014, 08:42 AM.

    Excellent post! This can also be applied to 24v guys very easily. I know I'm not running a mechanical fan. I can only think of one or two people who were willing/able to keep theirs.


      EDIT: After 3 years running on this setup I found that I always had issues running the m30 + A/C on + stop-and-go traffic + 90F ambient temps. The 16" Spal fan just wasn't cutting it for airflow with all the heat coming off the condenser added in. Why? I'm glad you asked!! Time for... SCIENCE!

      Essentially you're facing 2 issues when trying to run A/C in your m30 swap. If you live in a hot climate (SE or SW USA, Australia, etc) READ THIS!:

      1) The high-side pressure of an r134a A/C system (which most of us have converted to at this point) at 90F ambient is around 275psi. The saturation pressure or r134a at 275psi (i.e. the temp at which the gas condenses to a liquid) is 158F. If you're running an 80C/176F thermostat this results in a delta-T (temp difference) of 18F. Which means that you're doing essentially zero cooling. The air coming off your condenser is nearly the same temp as your coolant, and therefor cannot absorb any additional heat!

      2)The standard e28 535i radiator has frontal (2-D) surface area of 408 square inches (575x558mm). A 16" fan has an area of 201 sq in, or less than half of that. And if it's mounted on your condenser it means that 100% or nearly 100% of your forced air will be hot as balls (technical term) when it hits the radiator.

      You need to find a way of providing forced air to a larger area of the radiator, specifically the parts which are NOT behind the condenser.
      My first task was to find out just how much fan I could fit on the engine side of the radiator as a puller. Using the excellent drawings that Spal provides on its website, I made a cardboard mockup of several sizes until I finally settled on a curved-blade 10" model. It will fit right in front of the alternator in the upper left-hand corner of the rad which, conveniently, is also where the 16" pusher doesn't have any overlap (meaning that when I'm not moving, that part of the rad is doing 0 cooling).

      In the photo below you can just see the 16" fan off to the left, and the area on the right which doesn't see any air movement. The 10" fan sits directly behind this area, providing sweet, sweet cooling air.

      Once the fan arrived I was able to test fit it and confirm the clearances. Talk about a tight fit!

      Next up was to mount it permanently. I found a great type of zip-tie at the local Napa auto parts. They're listed as parts for an automatic transmission, not sure why :shrug:

      Then I had to decide on how I wanted it to be triggered. The 16" pusher is on the 80/88C aux fan switch with a manual override switch in the center console, so I knew I wanted it on the same system. But rather than fork over another $50 for another Spal resistor I decided to only have it run on HIGH and come on at the same time as the other fan. So I ran a new 12V source:

      Wired up a relay I had laying around:

      I tapped in to the stock aux fan wiring for a trigger, and boom! The 16" pusher comes on at medium speed at 80C, and at 88C both fans come on at high speed. Hopefully this will take care of the issue!

      Alternatively, if you REALLY wanted to go balls-out fancy, you could stick a 90C fan switch in the 2nd spare radiator port (all e28 535i radiators have 2 ports) and have the smaller 10" fan come on at 90C. Then each level of cooling is triggered at truly different temps, making all females panties within a 2 mile radius instantly wet with joy. Or you could invest in one of the new variable speed fans that many companies are making now days. They allow a fully programmable speed ramp-up from 50% to 100% over any given temp range you want. Very cool, very sexy, and surprisingly affordable.
      Last edited by CorvallisBMW; 03-13-2014, 08:43 AM.



        The timing of this post is uncanny. I actually just ordered a Spal 30102047 last night to replace my Permacool "Finger-Chopper". I was having all kinds of low speed overheating problems which, after some creative testing with some 500 mph tape (don't ask), seem to be because of extremely poor ducting. The Permacool has absolutely no ducting at all, not even a ring around the blades to direct the air forward. For reference here's the Permacool unit:

        I will have to follow suit and post a little write up when I get done with my latest additions.
        $500, Diamantschwarz, and a Dream


          excellent post. subbed for later use.
          Originally posted by LJ851
          I programmed my oven to turn off when my pizza was done, should i start a build thread?



            good post. I agree with all you said. However another problem that so many e30 m30 users face is air in the system. I don't know about you but it's always a bitch bleeding air from the lines. A negative effect of that, other than bursting hoses is the fact that sometimes the coolant never reaches the sensor hence the fan never turns on automatically.
            Recent Rebranding!!
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              Thanks! I'll order 61-31-8-361-787 as I have my spal fan on at all times, keeps it nice and cool :)
              Mtech1 v8 build thread -

              OEM v8 manual chip or dme -


                Originally posted by FrankM E30 View Post
                good post. I agree with all you said. However another problem that so many e30 m30 users face is air in the system. I don't know about you but it's always a bitch bleeding air from the lines. A negative effect of that, other than bursting hoses is the fact that sometimes the coolant never reaches the sensor hence the fan never turns on automatically.
                ahhh yes, that damn thing. Honestly I think I cracked the bleed screw 2-3 times every day for the first week I drove the car, and every time some air came out. I can see how the sensor would not trigger the fan if some air was trapped in the top of the radiator.

                Again, it's all about proper bleeding. Raise front of car, raise expansion tank, squeeze hoses and bleed, bleed, bleed!

                Also i don' know about everyone's e28 radiator, but mine has 2 ports for sensors. I made sure to locate mine in the lower port.


                  Thanks you all the info, about to drop motor in and Im going to be needing this soon.
                  E30 M30B34 Mounts Available


                    When I did my swap I used one of the Hayden fans from the local auto store. I just had it wired up to a toggle, but you can get the relay kit with the temp probe that is inserted into the radiator. Not sure how reliable those are though. Which is why I had mine on a toggle. Never had any problem with air though. Probably because when I first put coolant in it the front end was on ramps so it was definitely elevated plenty!


                      Awesome. I've been searching for a while for a decent fan and a lower temp switch!
                      '86 E30
                      '05 E53 X5
                      '72 Firebird
                      '10 Prius
                      '03 Tundra


                        I just saw this little gem on the Spal website, so fucking cool!!!


                        If I ever have a need to replace my current setup I'm going this route.


                          I drove mine for the first time tonight. 14mi to the exhaust shop and it was all over the place. It would always cool back down to almost half but then go right back up again. I have let a ton of air out and it keeps coming. Still waiting to put the water wetter in, need to do that soon. I did it on my sloping driveway heat on and still has air.

                          At the moment I am using an E34 Aux fan. Need something bigger though.



                            where are you guys putting the switch/sensor?

                            Need Illustration or Design work?


                              It goes in the radiator