onefastrx7turbo

Hello friends, I decided to share this with RX8 community after some research on cooling system operation and modifications. I want to preface this by saying this might not be for everyone but here in Phoenix, we see 112F+ during the summers pretty regularly and our cooling systems seem to struggle in shedding the heat load. I was disappointed at Mazda's decision to only put one oil cooler on the auto cars. Perhaps their rationale is the lower RPMs put less stress on the cooling system (oil and water) and they would not be pushed as hard as the manual cars. While I generally agree with this, the fact that there is a transmission cooler built into the radiator means that the radiator now has to manage the heat from the engine AND the transmission. This puts a higher load on both the water and oil cooling systems and it's my opinion only having 1 oil cooler on these cars in our hot weather was a mistake. Perhaps in Seattle where it rarely gets over 85F in the summer, this was sufficient, but the Southwest of the United States is a unique environment.

I started researching the oil coolers and lines to add the second oil cooler to my car while I have the engine out for overhaul. I started reading through the posts regarding oil temperatures and thermostats and was somewhat horrified to find the stock RX8 oil cooler thermostat didn't open until 230F!! I understand why Mazda did it, but 230F is unacceptable to me. IRP performance sells a thermostat which opens at 180F. I wanted to see if the FD RX7 and RX8 oil cooler thermostats were interchangeable. I bought two FD oil cooler thermostats and tested them for opening temps and was happy when I was able to verify they did open at 140F! I also tested the RX8 thermostat and despite the water boiling and my stove on high with water temperatures reaching 225F, I could not get the RX8 thermostat to open. I bought both oil coolers and the lines from a junkyard local to me and will install the second one before the engine goes back in. Also, I am going to swap both my RX8 oil cooler thermostats with the FD units and hopefully give my cooling system an advantage of both the second cooler and the lower thermostat opening temperatures! *Note, I posted this in the S2 forum because I am doing this on my S2, but I suspect this would work for S1 as well.

both FD thermostats on top, the RX8 unit is the one with the O ring still on it


Tested the opening temperatures on the FD units and found they both opened by 150F

TeamRX8

iTrader: (25)

There are several threads in the S1 area for the slightly higher temp aftermarket version. Cooler isn’t necessarily better, but the OE t-stats are too high temp for sure. However, I’d rather have the engine coolant a bit on the low temperature side rather than engine oil. The aftermarket t-stats are pricey for what they are though. Those should probably be ok since you live near Phoenix. Might be too cold for Canada.

A couple threads on here to remove and block the factory t-stats to instead use an aftermarket type plumbed into the oil cooler lines, either with or without a remote filter. It costs more and takes more effort to install, yet has some benefits for track/competition or turbo conversion in hot weather. The factory type are known to leak the bypass path around the cooler. Oil still flows the entire circuits with that design too whether open or closed.

The aftermarket plumbed in version always sends a small amount of oil to the coolers during bypass, but the majority being bypassed is short circuited from the entire cooler line path back directly to the engine instead, resulting in less backpressure when cold, being more efficient, adjustable for different temperature setpoints, etc.

onefastrx7turbo

Hi TeamRX8! Good to talk to you. Yea, I read through that other 9 page thread which was sort of what sent me on this path. I am not knocking any vendors with this, I greatly appreciate what they're doing for the rotary community and I wish them all the success, but I didn't want to pay $180 for replacement thermostats if there was another option. I 100% agree with you about cooler isn't always better, which is exactly why I think people need to consider the environment their car is operating when choosing to modify their car. A person living and driving in Alaska won't have the same environmental factors as someone in Dubai, as an example. But for me, in Phoenix where we just set yet another heat record with 50+ straight days of over 111F degrees each day (the previous record being 32 days), my cooling system needs any assistance I can give it. This last summer when driving at low speed with the AC on, I was seeing coolant temperatures in the range of 212-216F and I didn't like that one bit. Now I know that even with oil temperatures likely in the same range, the thermostat still wasn't even open allowing full circulation through the cooler. My intention is to give the oil system an additional oil cooler and lower the operating temperature of both in an attempt to try keep these temps as low as possible here in the Phoenix summer. As I type this, my phone is reporting 116F ambient temperatures outside.

I don't track this car and I think the factory oil coolers are sufficient for normal street driving, so I just wanted to try and improve on the factory system a bit. Once I put this motor back together I can see if there was any benefit to this.

cheers!

kevink0000

Onefast,

I live in the PHX area also, and cooling this car in those conditions is not easy. I swapped out the stock oil thermostats for the aftermarket units mentioned, and that helped to a point.

The best thing I have done so far was to add a second coolant radiator. I used a Chinese Ebay Polaris 900 three-row aluminum radiator. It only has 1" fittings so I plumbed it in parallel with the "high performance" Koto radiator the car came with. It is mounted in front of the AC condenser. I tried different positions, but found this to actually work the best, without its own fan. I know the kind of temps you are talking about, and was not happy with the cooling in either of the 8s I have. Try going up north on a 115 degree day on I-17!! The stock system cannot handle that at all. You literally have to pull over and shut down before you get to Sunset Point.

The coolant gets overly warm and that overwhelms the oil coolers, is what I have found. I was fortunate to buy my 2nd rx8 with gauges already installed, so it was easy to see what is going on with different changes. I have all the foam, under tray, etc to spec. The battery and the airbox is still in place. The airflow to the radiator is not good, but it also has a small size compared to other Mazda rotaries, of less power output. If you compare core size vs output, only the FD is worse.

The added radiator made the biggest difference of any mod, which includes the FAL 480 fans. The fans actually did not help much vs the stock units. In the summer, I run them at high speed all the time. I like A/C. I also use the Mazmart thermostat, FWIW.

I also added small motorcycle fans behind the oil coolers, because they would heat soak under certain conditions and never recover until the car was moving at interstate speeds again, or was shut down for a stop at a store or work, etc. The drive-thru line after highway speeds was a killer! The small fans helped that. It no longer happens.

I am still not 100 percent satisfied, I still cannot run at anything like full power in the heat for a length of time, so on my second 8 which is slowly getting rebuilt, I intend to use a larger second radiator, from an aw11 mr2, with the oil cooler therms and fans. The aw11 radiator can be plumbed in series, which I will try on that car.

With the system I am currently running, the oil will reach a bit over 210 max at the output line before the coolers. The coolant will get to just under 200 in the same conditions. This is running down the highway. That is why I want to go bigger still on the second radiator. By the way, at lower speeds, the system can actually keep temps in check better. The engine output at a given time/temp is the determining factor in my system currently. In sub 100 degree temps, the thermostats are allowed to maintain temp properly, and I get 174 coolant and oil at 195 at the output, rock steady all the time. In my opinion, steady temps regardless of output/ambient temp are a key for longevity for any engine, but especially this one.

I am interested to see what you come up with to cool your car also.Take care!

onefastrx7turbo

Hi Kevin,

Thank you for the thoughtful feedback! To be honest, I was worried someone like you would chime in and say exactly what you said; that despite modifying little things here and there, it's still not enough. I did some limited data logging before the coolant seal went and my observations were similar to yours where at low speed or stopped, the temps with the A/C on continue to climb and heat soak until you start moving again and you reach +40mph and then the added airflow across the cooler and the radiator started reducing temperatures. At one point, I saw 168F intake air temperature and 212F coolant temperature but I was unable to measure oil temperature. Once moving again, the coolant temperatures dropped down to 202-205. I'm still somewhat amazed that Mazda signed off on the cooling systems of these cars during testing. They had to have known about these problems with high ambient temperatures?

A few questions for you, perhaps we can start a data point map and see if there is a good way to solve these cooling issues.

• You mentioned you are running the 180F oil thermostats, I will be running the FD oil thermostats which open 30F sooner. I doubt this will make much of a difference once the oil reaches +180F degrees, but maybe it will help keep the oil temps lower for longer?
• Is your car a series 1 with a series 1 radiator? Same with the oil coolers? I don't know whats different about the series 1 VS series 2 oil coolers, but the P/Ns are different
• I'm using the stock Mazda coolant thermostat, you mentioned you're using a lower temperature unit
• I'm planning on changing the coolant ratio of the FL22 to roughly 60% distilled water to 40% coolant
• What oil do you run in the summer and winter?

kevink0000

The FD thermostats will probably be able to maintain whatever their equilibrium temp is once the coolant heat overload issues are fixed. They will probably be fine to use in AZ.

Both cars in my experience are s1 with mt, therefore dual oil cooler cars.I am not sure what the differences are.

I use fl22 at about 40/60 as you mentioned.

I use GTX20w50 year round, and will continue to do so. I have posted oil analysis results in the Used Oil Analysis thread. I am happy with the results when compared to others there.

My 2007 s1 with 186000 miles failed when an apex seal cracked and the broke completely. I saw evidence of melted coolant seals also when I pulled it apart.It was not leaking yet. It was a car that had spent all its time in the LA area. These engines are allowed to run too hot in my opinion for long life. I share your amazement that Mazda put this size radiator in this car.

kevink0000

Also, Is your car an automatic?

onefastrx7turbo

Good info, Kevin. Yea my car is an automatic so the radiator gets to cool the engine and the transmission. I did change the trans fluid to Valvoline Maxlife synthetic fluid so maybe that will run a bit cooler than the stock fluid did. I agree with the 20w-50, I ran that in my NA FC year round in the valley with good results.

onefastrx7turbo

I can tell you that so far, the coolant will hover in the 200-207F range in traffic with the AC on and the ambient temperatures @ +95F. After getting on the freeway, the temps drop very quickly to 195-197. I cant measure oil temperature, but it seems to cool off much quicker now with the dual oil coolers and the FD thermostats.

TeamRX8

iTrader: (25)

still say the best thing to do is to remove the OE cooler t-stats, block the bypass passage in them, and put a true single t-stat between the supply and return hoses to short cut the coolers in the bypass mode. Some work and cost to doing that though, so not for everyone.



.

.

.

onefastrx7turbo

Absolutely true. For the most precise oil temperature control, this is the best solution. For the RX8 though, I'm trying to keep it simple and OEM where possible just to reduce complexity. My rotary FD and my V8 FC are modified enough to keep me busy haha! I'm using a thermostat like this on my FD, in fact.

onefastrx7turbo

Just periodically updating results from what I can measure. Yesterday I was on the freeway with the AC on and the car indicating 112F outside air. IATs were 122F and the coolant stayed between 195-199F indicated on my scangauge II. I'm pleased with the cooling performance so far. Im not sure how much of it is due to the dual oil coolers + lower temp thermostats or the new radiator and the foam around the radiator, but I'm getting good results.

txbdan

Hey all,

How does one delete the OEM thermostat all together? I'm running an external thermostat so just need the OEM oil cooler to pass through as it does when hot.

Thanks

TeamRX8

iTrader: (25)

I thread tapped the bypass oil passage hole in the cooler and screwed in a low profile allen head screw to block it, then disassembled the t-stat from the outer cap.

there’s one or two threads in here discussing it, but maybe like looking for the needle in the hay stack …
.