Installing a bigger radiator


What drives this is that cool is fast. Based on experiments I watched Chuck Baader and Jim Levie conduct, hp starts dropping at about 204 deg. I’m told that this is a product of the DME retarding ignition timing.

It’s easy to find bigger radiators. They are available from circle track suppliers for $200ish. Pick a rad based on it’s dimensions, port locations, and inlet port dia. The outlet port is almost sure to be too big. The frame rails limit the radiator’s width. The design of our hood will allow a little more radiator height.

Location of the outlet. Early model cooling has the outlet at bottom left. Late model at bottom right. You’re going to find lots of triple pass radiators that match the early config, and double pass radiators that are similar to late config.

I settled on early config. 2x I set up a late config big aftermarket radiator, but each time it was kinda a pita. The OEM late model rad has the outlet at bottom right. But the big doublepass aftermarket rad has the outlet several inches above bottom right. This required cutting the late model steel coolant tube that is in front of the engine, a bit short. I also played around with modifying the rad outlet, and I screwed around with hoses a bit trying to make it all work well.

I’m not saying the late cooling config can’t be done, if you were smart about it, you could do it just fine. Much of my problems here was that I ended up with a rad outlet modified (pointed) in a direction that didn’t work as well as I’d thought it would, so I monkeyed around a lot trying to make the kludge work. Do better on how you mod the rad outlet and it will go easier for you.

It’s important to point out that having a coolant pressure switch is a huge comfort. With a coolant pressure switch wired to a huge light right in front of your face, you can take your car on the track with a solution that is less bulletproof than the fabulous solution we’d all hoped for. Don’t monkey around with your cooling system until you have a coolant pressure switch. Then test your mods well before your next event. If your happy-ass mods spew water all over the track, you’re going to have some upset buddies.

The early cooling solution, for an aftermarket rad, doesn’t require the dicking around described above.

Modifying the outlet port. All solutions require this. IIRC you’ll find all sorts of rads with a 1.5" inlet port which works for us. But the outlet ports are all 1.75". Measure your shit to make sure I’m remembering these #'s right. So the outlet port is too big for our hose. I poked around looking for hose dia. adapters but I never found one that I liked. So what I ended up doing is modifying the AL hose outlet itself.

Welding the outlet port to change it’s dia. and orientation. Each time I took, with the rad, a 1.5" AL tube. For the late model attempts I had the welder not only cut the 1.75" port off and use a piece of tube to make a 1.5" port, but also change the length and orientation of the port. As mentioned above, the OEM port is lower so I was playing around with port orientation such that I could make the rad port play nicely with that late model steel coolant tube. For the early model attempts were easier. The 1.75" port just had to be swapped out with a piece of 1.5" tube.

What I finally settled on was JBWeld. I know that seems crazy, but it’s important to understand that the radiator outlet is not really under any pressure at all. The radiator outlet is a lot closer to the pump’s intake, then it is the pump’s outlet. As a result, the pressure at the radiator outlet is either 0 or a bit negative. So the only real stress on the outlet is vibration, unless you do something dumb with the hose. So I cut the 1.75" outlet down a bit so it wasn’t too long. Then I globbed some JB Weld on to a piece of 1.5" AL pipe a couple times, letting it dry, to increase the pipe’s dia. until it was starting to fit snugly inside of the 1.75" stub. Then I put a final coat of JB Weld on to the 1.5" AL pipe and stuck it in the 1.75" stub. Once that dried, I slathered more JB Weld on to the outside of it all.

So this last time I didn’t need any AL welding done at all.

The difference between early and late model coolant systems. It’s all about the water pump. The early pump has an extra port on it that goes to the reservoir. With a bit of cleverness tho, you can make a “T” that will connect an early reservoir to a late pump. Chuck Baader made a couple of these for me, over the years.

Note that “it’s all about the water pump” depends on whether or not you have a hose between the back of the head and the thermostat housing, because that’s where the new model reservoir connects to the system. At least, I think that’s right, me never having owned a late reservoir. For me, that coolant line is blocked at the head and the tstat housing, reducing the # of places my coolant system can fail.

One time I had a late water pump and I had problems with Chuck’s T. So my early reservoir wasn’t going to work and I didn’t have a late reservoir. So after doing some thinking about “just what is it that the reservoir really does?” I tried no reservoir at all. The aftermarket rads come with a radiator cap, so there’s a place to add water.

The “no reservoir” solution seemed to work fine, but it didn’t seem “legal”, so that kludge didn’t last long. Also, I read that the reservoir did, in fact, have a purpose. Apparently cooling systems were more efficient if there was a “still” volume where dissolved air could come out of solution.

Radiator cap. OEM rads have no cap, only a small hose to the reservoir. Aftermarket rads do have a cap, and altho they have a hose port there, the port is designed to go to over-flow, not to the reservoir. It took me years to finally figure out how to fix this.

The problem is that a radiator cap is designed to seal unless the pressure gets too high. If that happens the cap will open up and allow water into the over flo hose. If you install the rad in your car and connect that hose to the reservoir, water will come from the reservoir and exit the rad at the cap. This is because the cap’s seal is a spring loaded thing BELOW the port and you just brought water to the cap ABOVE the seal. It probably won’t be a crisis, but you’ll find yourself adding water between events.

One solution was to weld on a plate to seal the radiator port. I tried a number of different rad caps, some with the conventional spring loaded lower seals, some with (what looked like) only an upper seal. Nothing stopped the slow leaking. Hell, it took me prob 2 years to figure out that the leak even was the at the radiator cap. It only happened when the engine was at operational temp and at high rpm. By the time I came off track the little bit of wetness had dried up so there was nothing to find. Diabolical.

What I finally did was JB weld an AL plate instead of a radiator cap. Much cheaper then having the welder do it. That was 4yrs ago.


I am not understanding your cap seal issue. There are blank caps out there. Look for nissan 2005-2015 xterra or any nissan V6. They have a blank cap to on the radiator and the radiator "overflow is connected to a pressurized reservoirs just like our cars.



I tried 2 radiator caps like that. Neither would stop the little leakage when the rad was hot and at high rpm. Sure seemed to me like they should have worked. I did not understand why they didn’t. Maybe the next guy will get it to work.


Have you tried putting a normal cap in there? Just to test it out?


I tried all sorts of cap types. I also modded cap types trying to fix what I perceived to be reason that cap type didn’t work at first. Nothing worked until I JB Welded the SOB on.

Don’t let the fact that I can’t explain why one idea failed and another worked weird you out. I’ve all sorts of examples of that kind of stuff. I had some crazy oil pressure problems an Accusump in 2009(?). If I told folks the details of the crazy symptoms of that problem, and with 4 oil pressure gauges I could see what was happening everywhere, folks would either have to accept that the cause was the existence of alternate dimensions of time and space, or Sauron of Mordor, or that I was an idiot, or that I was a liar.

So I don’t talk much about that particular story.


I don’t believe you need a bigger radiator, I believe you need a better radiator.

93-99 BMW E36 M3 3.2L CSF 2 Row High Performance Aluminum Racing Radiator 98 97 93-99 BMW E36 M3 3.2L CSF 2 Row High Performance Aluminum Racing Radiator 98 97: Automotive


I bought this last year, beautiful, efficient, fits and is not going to add a shit ton of weight over the front of my car


Is this one also a good choice? I have always heard good things about Mishimoto, and it says it fits E30/E36 6-cylinders. It costs about $42 less than the CSF, when shipping is considered.


Mishimoto radiators have been a common upgrade for us, but I don’t know anything about their models nor fitment. I looked at the Amazon link and it says that it will fit an E30.

This isn’t really a precision issue, so you should be good. As long as a radiator isn’t too wide or too tall, you can make it work. The charm of the rad in your link is that the outlet is prob the right dia and the inlet is prob exactly right for a late model cooling system. Therefore you shouldn’t have to do any modding.

Looking at the pics, there’s a port near the outlet that looks a bit big, but that should be easy enough to deal with.

The E36 rad has an expansion tank on the rad itself. That’s the box looking thing on the side of the rad. Not necessary for us, since we have an external expansion tank, but not a problem either.


It seems most aftermarket radiators are designed for the late model.

Here is from a company I usually buy my radiators from.