Overheating on fwy with AC on during hot weather

[Cisco Kidd]

I replaced the mechanical fan with the mishimoto and kept the oem AUX fan. This combination has kept my temps perfect.

I have the same setup mine moves a bit still if im burning down the freeway and temps are 100+ in the summer but as stated in the manual its normal for our cars to jump a bit. ive had the setup maybe 4-5 years now with no real issues aside from adjusting the fan control here and there cause they tend to run for longer than need be.

[Johnvu]

So a single mishimoto fan had a better result than the 2 fans(engine fan + aux fan) that come stock?

I replaced the mechanical fan with the mishimoto and kept the oem AUX fan. This combination has kept my temps perfect.

[yhp2009]

I had this same issue on hot Houston summer days. I ended up getting Mishimoto electric fan kit and it solved all of my overheating issues. My water temp gauge never goes beyond the center now.

So a single mishimoto fan had a better result than the 2 fans(engine fan + aux fan) that come stock?

[cozmo kraemer]

What I noticed today after driving some more is while driving up hill at a constant 75mph on the fwy, both the engine temp and water temp rises as well. I had to ease off the throttle and slowly go up hill at 65 to get the temps back to normal. At this point it seems like my radiator cant cool my engine sufficiently. Should I replace it with a genuine OEM radiator which I usually buy from FCP or are there any brands that will perform better than stock?

Most people on here will recommend stock. It is sufficient, even for track use. There are not very many aftermarket options that improve upon it.

[Johnvu]

I had this same issue on hot Houston summer days. I ended up getting Mishimoto electric fan kit and it solved all of my overheating issues. My water temp gauge never goes beyond the center now.

[NaM3]

What I noticed today after driving some more is while driving up hill at a constant 75mph on the fwy, both the engine temp and water temp rises as well. I had to ease off the throttle and slowly go up hill at 65 to get the temps back to normal. At this point it seems like my radiator cant cool my engine sufficiently. Should I replace it with a genuine OEM radiator which I usually buy from FCP or are there any brands that will perform better than stock?

[cozmo kraemer]

I dont run a clutch fan at all. I just run the stock Aux pusher fan. I never have any problems with overheating even under load going up hills in 110* heat, nor stop and go in 100+. Lucky enough for me, I don't see days that hot anymore after moving to the coast.

[nogoodname]

Mine would heat up like that and I heard nightmares of the clutch fans letting go (local cars). So I went with an electric fan with an adjustable fan controller. No problems now. Original Tsat and water pump.

[0-60motorsports]

I have the exact same issue going on for 2 years now. I am for the first time, lost. One last thing to try is a genuine BMW Fan clutch which was ordered a week ago and will be here in a month i think due to issues with BMW supply.

[NaM3]

Ah! I didnt think about my coolant mix ratio. I have been using a 50/50 mix.

On a hot day to me is around 90 degrees +

[Icecream]

Thanks for all the info. As for my car, the temps would creep up to almost 3/4 for the water temp and a little less for the engine temp. This would happen while driving in traffic on the fwy, the temps would climb while I am not moving and would drop if I turn off my AC

What is your coolant mix? Going 30/70 coolant/water, if your climate allows will help. If that doesn’t work, I’d look at your nissen radiator and compare to OEM if everything else has been replaced. May be just slightly different in size/construction to make a difference. Also, how hot are we talking? If this is happening on 110+ days, I’d not worry so much to be honest (other than adjusting coolant ratio, maybe add a bottle of water wetter if you want to experiment).

[NaM3]

Thanks for all the info. As for my car, the temps would creep up to almost 3/4 for the water temp and a little less for the engine temp. This would happen while driving in traffic on the fwy, the temps would climb while I am not moving and would drop if I turn off my AC

[old///MFanatic]

OP basically what’s happening is the AC has its own mini heat exchanger “radiator” in front of the main engine radiator. When both need to exchange heat off, (like when AC on in hot weather)the cooling system should take care of it. Constant hot air makes it harder to accomplish.
Now when all fans, pump and t-stat work. Often this is a main radiator issue being clogged or having dirt and debris in fins inhibiting it from performing fully. Since you replaced that and other things, the first I would do is bleed the system again. Next the temp switch in lower radiator hose is something I would look at. The 2 o-rings on the metal sleeve from water pump get pinched on occasion. And if anyone put any type of “stop leak” in system before your new parts were installed that’s always a fun load of crud that messes with the system.

[old///MFanatic]

OP... I would guess this is your fan clutch. Once it starts to die it obstructs air from traveling through the radiator at speed. I had this issue in Phoenix summers. Funny enough, I removed the clutch fan completely to help while the new clutch was on order, and never had the problem again.
I see you said you replaced it.. but that is what sounds like the issue. Or your aux fan isn't running correctly. I had it happen on an e30 I had...same issue..overheat with AC on in super hot PHX

Wow that’s an interesting story it being your vis-fan. At frwy speed it really shouldn’t be engaged anyways. For it to hinder the air from the front from coming through AC radiator and then engine radiator is surprising. Good to know.

[old///MFanatic]

I don't believe Nissen is the OEM for the e46 M3 rad (not 100% certain on that, but pretty sure).

Correct MODINE is OE for the E46 M3 radiator.

Nissens is a legit radiator too. Think it’s OE on the non-M E46.