We have a customer that brought us his 99 miata with LS6 swap, swap was done by someone in another state, and appears to be done well. He complained about it running pretty hot, and temps not wanting to come down. It has a thing dual pass radiator and 2 10" puller fans with shroud, chinese no name. I installed a 160 degree thermostat and bled it properly. The temps still get up pretty high but will come down a bit. I noticed that IAT was getting very high and built a fully sealed air box for the car and the IAT have dropped over 30 degrees and coolant temps are a bit better, but still high, 220-230. I think it needs better fans and relays on each fan, but this should not be a factor while cruising. The only thing I have been told is this problem started when the splash sheild and fender liners came off at the road course, but I dont think the splash sheild should have that much of a effect on it but I could be wrong. Are these engines common to have water pump problems? the pump is pumping, but maybe it has a problem with the blades and is not efficient anymore? Looking for a little insight into the problem.

 

Oil temps good?

I know the splash shield under the car does make a difference, and is not expensive to replace. Might want to try a Stage 2 Flyin Miata airflow kit and crossflow radiator...

 

I've got an LS6 in my '01 and have no overheating problems even in the recent 90+ heat here in Maryland. The fans aren't doing the cooling at cruise anyway.

If he is having overheating problems at cruise he has air in his system still. Bleeding these LSX cooling systems has always been problematic for many of the swappers. I had no issue by installing a petcock valve in the upper radiator hose at the highest point of the cooling system.

This is what I use in the upper rad hose. It has the steam venting fitting and a valve to make bleeding way easier.

http://jagsthatrun.com/Pages/Parts_Cooling_LSI-tee.html



Also, having the shield and blocking the sides of the radiator is very important to get air flowing through the radiator (and through the nose opening) and NOT around and under it.

I used a simple aluminum sheet under the radiator and attached it from the bottom nose opening to the bottom of the radiator with some sticky heater shield tape. My radiator is wide so there isn't much room for air to get around it.

 

I drilled a 1/8th hole in the flat top of the waterpump housing and installed a close nip to a brass T. Then hooked that to the steam vent tubes under the intake. When I filled the collant I took the plug off the top of the T to let air out. When the rad wouldnt take any more, I poured a little more in and installed the plug again. It helps to have the front of the car raised a bit. My car runs 210 all day long with only one stock fan running.

 

Might want to try a Stage 2 Flyin Miata airflow kit and crossflow radiator...

 

Concur. I've never even seen a V8 Miata up close (yet), but I've dealt with airflow and cooling issues in numerous other situations. The idea is to give air NO OTHER CHOICE but to go where you want it. In this case, directing the air in such a manner (blocking alternate paths, adding a chin spoiler/scoop/whatever of some size, etc.) will pay huge dividends.

Remember, if air can go in some direction other that that which you desire, it will. Just because it can.

HTH,

Lynn B.

 

It does sound like some air in the system. Is he running 50/50 coolant and water? Might want to use a little more water and less coolant OR all water with some water wetter. I had some cooling issues with my 5.0 swap and when I switched to running straight water it helped it ALOT! The problem that I had was when sitting in traffic the temp would climb and then drop back down when cruising.