Cooling questions – seeing conflicting info

[IamFODI]

For these items…

1. Engine oil cooler
2. Main radiator
3. MTF cooler
4. PSF cooler

…Are there any aftermarket options that are proven to work better than good-condition stock coolers, assuming a stock engine bay and underpanels? If so, how much better?

I know credible people swear by do88 and CSF. But I’ve also seen posts (sometimes from the same people) suggesting there’s not much improvement to be had vs. stock. That lines up with my understanding of cooling system theory, i.e. bigger radiators won’t help much if airflow is the limiting factor, which it almost always is. So, it’s hard to know what to think.

I’ve also read that the oil diverter valve mod helps a little, and higher octane fuel can help fairly significantly. Bimmerworld also apparently likes to control oil temps with engine oil choice.

What else is out there that has a track record (pun intended) of improvement vs. just replacing everything with new OE?

[davidinnyc]

Bumping this. I’m probably going to need to upgrade / refresh my oil cooling system and am curious of the options. The BMW system refresh kit on FCP/ECS is $1,800 and when I see a CSF oil cooler for $550 I get curious.

[IamFODI]

Bumping this. I’m probably going to need to upgrade / refresh my oil cooling system and am curious of the options. The BMW system refresh kit on FCP/ECS is $1,800 and when I see a CSF oil cooler for $550 I get curious.

Thanks for the bump. I've done some learning since this. Long story short, I'm leaving everything stock, replacing the main radiator and oil cooler with new OE pieces whenever it’s time.

There are many types of radiator construction; here are two:

1. Tube-and-fin – more efficient at rejecting heat into the airstream, thus better for sustained cooling capacity; also lighter

2. Bar-and-plate – able to hold more heat due to more thermal mass, thus better for short bursts of heat; also less expensive and more durable

The stock main radiator and oil cooler are tube-and-fin. CSF and do88, like most aftermarket options, are bar-and-plate. Presumably this is why CSF and do88 radiators and oil coolers don't unequivocally reduce temps even though they’re bigger than stock (with the occasional fitment challenges that come with that) and heavier. Sometimes people find them effective, e.g. for drag racing or the first half of a track session – or when “upgrading” from failing original coolers. Sometimes they don’t, e.g. in terms of peak temps at the end of a full track session.

So far I’ve seen only one aftermarket brand offering larger-than-stock tube-and-fin oil coolers for this platform, and that’s Litchfield. Haven’t seen any feedback on those.

I’ve repeatedly heard informed people say the most important factor in the cooling system usually isn’t the size of the cooler; it's the airflow. Air needs to get to the cooler, through it, and away from it. This is why the factory oil cooler has a duct behind it that connects with the factory underpanel, which is shaped to provide a low pressure zone at the duct's exit. All of this is the main reason why I’m still on the factory undertray. I have yet to see an aftermarket option that takes that airflow aspect seriously, let alone implements it with credible competence. Happy to be corrected if I’m wrong.

I have yet to see hard evidence suggesting the stock MTF cooler isn’t enough. I might remove the factory block-off plate but I have no plans to replace the cooler.

There’s more of a feeling that a bigger PSF cooler can help, but… has anyone actually demonstrated that these power steering systems have a real problem other than leaking out the vent hole in the reservoir with hard use? There doesn’t seem to be consensus that a bigger cooler moves the needle on that. So, I’m not touching that either.

Hope that helps.

[bigjae46]

Thanks for the bump. I've done some learning since this. Long story short, I'm leaving everything stock, replacing the main radiator and oil cooler with new OE pieces whenever it’s time.

There are many types of radiator construction; here are two:

1. Tube-and-fin – more efficient at rejecting heat into the airstream, thus better for sustained cooling capacity; also lighter

2. Bar-and-plate – able to hold more heat due to more thermal mass, thus better for short bursts of heat; also less expensive and more durable

The stock main radiator and oil cooler are tube-and-fin. CSF and do88, like most aftermarket options, are bar-and-plate. Presumably this is why CSF and do88 radiators and oil coolers don't unequivocally reduce temps even though they’re bigger than stock (with the occasional fitment challenges that come with that) and heavier. Sometimes people find them effective, e.g. for drag racing or the first half of a track session – or when “upgrading” from failing original coolers. Sometimes they don’t, e.g. in terms of peak temps at the end of a full track session.

So far I’ve seen only one aftermarket brand offering larger-than-stock tube-and-fin oil coolers for this platform, and that’s Litchfield. Haven’t seen any feedback on those.

I’ve repeatedly heard informed people say the most important factor in the cooling system usually isn’t the size of the cooler; it's the airflow. Air needs to get to the cooler, through it, and away from it. This is why the factory oil cooler has a duct behind it that connects with the factory underpanel, which is shaped to provide a low pressure zone at the duct's exit. All of this is the main reason why I’m still on the factory undertray. I have yet to see an aftermarket option that takes that airflow aspect seriously, let alone implements it with credible competence. Happy to be corrected if I’m wrong.

I have yet to see hard evidence suggesting the stock MTF cooler isn’t enough. I might remove the factory block-off plate but I have no plans to replace the cooler.

There’s more of a feeling that a bigger PSF cooler can help, but… has anyone actually demonstrated that these power steering systems have a real problem other than leaking out the vent hole in the reservoir with hard use? There doesn’t seem to be consensus that a bigger cooler moves the needle on that. So, I’m not touching that either.

Hope that helps.

People forget that these cars could take the punishment of a summer track day when new. A fresh radiator and oil cooler performs very well.

Correct, it is about airflow vs getting bigger radiators. The one change that made the biggest difference on my E46 was removing the fans. This significantly improved performance at speed and dropped peak temps by 15 degrees.