Overheating on fwy with AC on during hot weather

[NaM3]

I have been experiencing both my water and engine temp rising above normal during hot days with my AC on. If I turn off the AC, the temp will drop back down to normal after a few minutes. Is this normal?

The background of my car is that I have replaced the water pump, thermostat, fan clutch, and fluid with all genuine OEM about a year ago (8k miles ago). The radiator have been replaced maybe 30-35k miles ago with also an OE unit (Nissen branded).

I ran the pusher fan test via INPA and it turns on as it should.

Is there anything else I should be looking at? Is it my radiator that needs to be replaced?

[heinzboehmer]

Is this when standing still or when moving? Might help narrow down the issue. Also how high is "above normal"?

Regardless, no this is not normal. My temps are stable and stay "normal" with or without AC on.

[Arith2]

We need some numbers and parameters to help. Give us data and we can probably help you pinpoint it being abnormal or not

[Obioban]

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

[cozmo kraemer]

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

I thought it was Baer, or something like that, as OE. I think that is what came when I ordered from BMW. I can check.

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 have since never installed the clutch fan again and never had an over heating issue.

Edit: I see you said you replaced it.. but that is what sounds like the issue. Or your aux fan isn't running correctly (which is super rare on this car, but could happen - I had it happen on an e30 I had...same issue..overheat with AC on in super hot PHX weather).

[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.

[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]

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.

[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

[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]

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 +

[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.

[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.

[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.

[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?