C900 Cooling System Upgrades

[DrewP]

More upgrades to come, as my brother is keen to spec out some actual quality racing radiators for both of our 16V'd 99 builds, and I need to address cooling in my C900 rallycross car as well.

1st super simple question, do the later aluminum / plastic end tanked radiators cool better than the early soldered brass ones? I have a brass radiator in my hopped up '85, and after 5-7 mins. of hard driving when the weather is warm (~85*F+) the temp needle works it's way up and up and up.

I've never had this radiator hot tanked or flushed or anything, it may just need some love, but with Nissens aluminum radiators available for ~$120, if they cool better that's money well spent to me.

2nd - does anyone drill out more passages in the thermostat, or pull the thermostat plunger out for race cars? I have the 75*C fan switch and I think an 89*C thermostat in the car now, and until I've wailed on it for a good few minutes straight it always keeps the temp needle dead center all year round.

Thoughts on thermostats?

[Crazyswede]

More upgrades to come, as my brother is keen to spec out some actual quality racing radiators for both of our 16V'd 99 builds, and I need to address cooling in my C900 rallycross car as well.

1st super simple question, do the later aluminum / plastic end tanked radiators cool better than the early soldered brass ones? I have a brass radiator in my hopped up '85, and after 5-7 mins. of hard driving when the weather is warm (~85*F+) the temp needle works it's way up and up and up.

I've never had this radiator hot tanked or flushed or anything, it may just need some love, but with Nissens aluminum radiators available for ~$120, if they cool better that's money well spent to me.

2nd - does anyone drill out more passages in the thermostat, or pull the thermostat plunger out for race cars? I have the 75*C fan switch and I think an 89*C thermostat in the car now, and until I've wailed on it for a good few minutes straight it always keeps the temp needle dead center all year round.

Thoughts on thermostats?

you dont want to pull the thermostat out...you need some restriction in the head to aid in cooling. If you want to run without a thermostat just punch the center of the t stat out but run the remaining bits to aid restriction.

[DrewP]

^^ That's what I meant, sorry I didn't explain very well. Back at the shop, the owner liked to have the guys drill extra bypass holes in the large mounting flange to "get more coolant flow." That was the part that made me suspicious he didn't know what he was doing, but still.

Does removing the center plunger from the thermostat help with cooling under racing conditions, or does it just remove the possibility of that as a failure point, since there's no way it can become stuck closed while out on a stage?

[Geoff]

From my experience the aluminum radiators cool better. "k" agrees too, aluminum is more conductive than brass.

[DrewP]

I'd heard that they did, but never met anyone who could back it up with numbers.

I do know that the aluminum ones have the end tanks fail eventually, just like every other new car radiator. The brass ones you can't blow up and end tank or have a hose bung break off...

[Geoff]

Mine has held up for ~10 rallies and 50+ rallycrosses (including driving 4-6 hours round-trip to about 35 of those events) in a 99. I had one on my SPG for ~80k miles including a track day at Limerock (where it got the hottest) but never overheated it that I can remember. I think I bought at least one of those radiators used.

[DrewP]

Good to know. Looks like I'll buy one of those Nissens ones for starters and see where that gets me. We used all Nissens at the shop when we could get them, I think the only ones I ever saw explode were from failing head gaskets overpressurizing the cooling system.

[99Super]

Remember, the t-stat is a three-way valve that recircs part of the coolant back through the head (8v) or directly to the heater/water pump (16v).
If you remove the entire unit, the coolant just recircs through the pump and really doesn't push any through the radiator.
When cold, the thermostat pushes the coolant back through the head/heater, when warm/hot, both valves are open, when really hot, the recirc portion closes and all the coolant moves through the radiator.

I'd say, if you want to maximize cooling, the flange-drilling may not be a bad option, but increasing the heater restriction may work better.

John

[DrewP]

It also occurred to me when I was getting the A/C on my '93 900S working yesterday that I might not have the '85 wired so that both fans run whenever the thermo switch in the radiator turns them on. That's to say I am not certain if it runs the "A/C" fan all the time. '85 has all the A/C stuff removed.

Another thing to check out before the SCCA rallycross at Glen Helen next weekend!

[99Super]

I did something similar to my old 86 SPG. I deleted the A/C system, but left the fan wired to the switch so it became my on demand fan.

[Fraser]

I dont have the second fan , I dont have a heater and then I expect things to stay cool when the turbo is peaking at 25 lbs !and its the old brass type ! He he. Just watch that gauge and flick on the fan switch before any WOT stuff.

[hutch]

I did something similar to my old 86 SPG. I deleted the A/C system, but left the fan wired to the switch so it became my on demand fan.

Do you have a link or a quick how to for this mod?

My old SPG was wired this way and it was very helpful to be able to turn on the second fan when I knew it could use some extra cooling. I did some google-fu and lots of talk about the 'cooling fan mod' to have both fans turn on to cool the radiator, but being able to just push the a/c button to turn a fan on was very helpful. Or is it as simple as leaving the wiring for the a/c system intact?

[Mezzanine]

Drew, if you guys are going to get a run of 99 radiators made, I'd be interested in one too... assuming you're going over to a cross-flow style that relocates the cold side discharge at the bottom of the radiator similar to the 900 style. Getting one of these made has been toward the bottom of my to-do list for years now. Keep me in the loop.

[Mezzanine]

Is there a suggested water pump for 900s? I've had a Hepo brand pump running for a few years now, and it has worked out fine. I wasn't sure if this was an item to go after OEM on or not. Suggestions?

[Chouan]

Drew, if you guys are going to get a run of 99 radiators made, I'd be interested in one too... assuming you're going over to a cross-flow style that relocates the cold side discharge at the bottom of the radiator similar to the 900 style. Getting one of these made has been toward the bottom of my to-do list for years now. Keep me in the loop.

I will also need one of these.