When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I like this design, it is nice to be able to see everything through the Lexan. You have a good idea when the cell is nearly full to avoid spilling fuel, and if your pumps and surge tank are visible you can spot leaks much earlier. But if you are planning on running ChampCar I am pretty sure this design is specifically forbidden by tech, it was asked about for another car, a CRX I think, and he was told no way. He even proposed a mostly metal bulkhead with just a Lexan window to look through and that was shot down. doesn’t necessarily make any sense, but that is the ruling I have seen from tech.
I like this design, it is nice to be able to see everything through the Lexan. You have a good idea when the cell is nearly full to avoid spilling fuel, and if your pumps and surge tank are visible you can spot leaks much earlier. But if you are planning on running ChampCar I am pretty sure this design is specifically forbidden by tech, it was asked about for another car, a CRX I think, and he was told no way. He even proposed a mostly metal bulkhead with just a Lexan window to look through and that was shot down. doesn’t necessarily make any sense, but that is the ruling I have seen from tech.
Yea...I can believe chumpcar would say that. One of the many reasons we stopped running chumpcar. It is very nice to be able to see everything. For us, chumpcar doesn't run in the PNW as Lucky Dog is a far superior series so we don't need to worry about them. In our opinion, even though they changed the name...they're still chumps...
Oil cooler - engine oil temp postmortem
Tested the gauge using a tire pyrometer (probe type) and some hot water. Determined that the temp gauge is likely not the issue.
Next I pulled apart the coolers and verified several things:
The coolers are dual pass - there is a baffle between the in and out ports on the coolers
These coolers are the no-name ebay OE knock-off coolers that sell for $75-100
The top cooler was not full of oil
The bottom cooler was full of oil
The conclusion we reached is that oil was not being distributed evenly between the coolers. The oil coming out of the engine was likely going to the hotter of the two coolers because was the path of least resistance because hotter oil has less viscosity. So once one of the two cooler started performing poorly, that is where most of the oil went.
This phenomenon was confirmed by a friend that has experience with multi-radiator/multi-oil cooling systems on gas-turbine generators. Flow balancing was a constant issue and eventually had to be computer controlled to make it work.
I believe this problem came about because where I am currently splitting the oil lines coming out of the engine. In my latest setup, I am dividing the oil between the two coolers at the input to the top cooler. I went to this design to simplify plumbing. In the past, I had a tee fitting at the engine that split the oil immediately so the viscosity of the oil was a constant. However, this arrangement meant running two separate lines to the coolers.
Currently I am investigating a single cooler solution using an aftermarket cooler from several different companies. The benefits would be an easier installation and use of a cooler from a recognizable source that use known cooler construction. Cost wise, the cooler will be more expensive but plumbing costs will be lower. I'll follow up with the choice I make.
How the two coolers are arranged. Bottom cooler was doing all of the work The single input line connected to the parrallel plumbing spliter
Interesting. I wouldn't have thought that as a possibility. Question, would it to to run the coolers in series? Output of the first to the input of the second? That would force all the oil through both coolers right? I had previously assumed that's how they were set up. Would that be too much for the pump to push through?
Running them in series would eliminate this issue. A local racer has two cars, one is plumbed in parallel and one in series. He said the one in series has low oil pressure until it warms up then pressure is acceptable. These are both street ported engines. I think it depends on the pump being used and the regulators in the engine.
In the past, I plumbed a pro-built 12A IT engine in series and it worked just fine and had good pressure. That engine had a mazda racing rear regular and a shimmed front regulator. When that engine died the stock engine I replaced it with had scary low oil pressure on start up with the same coolers plumbed in series. At the time, I didn't think about what would happen when the oil warmed up. Since then I have always used a parallel plumbing setup.
So as a result of my recent oil cooling issues, I spent allot of time researching coolers. I reached out to several manufacturers hoping to talk with someone in engineering. My goal was to find a single cooler solution.
Fluidyne was my first call based on a recommendation from a famous racer and some posts on this forum. I called regarding their DB-30618 cooler but the engineer said that wasn't their best option for me. However he never followed up and I didn't have time to wait. Next I called Mishimoto and spoke to someone I would characterize as a salesman at best. I was interested in their MMOC-DP-L but I really don't like that it is powder coated and information regarding tube construction was sketchy. Then I called AFCO regarding their 80421 cooler. I love the radiator I have from them, but the person I spoke to could not provide me with the actual dimensions of the product and the person "that should know" was not returning calls. I have to remember not to tell a circle tracker that I race one them WAANKEL ROWTAREIES ......
I settled on an MHX-245 triple pass cooler from Improved Racing. https://www.improvedracing.com/mhx-2...il-cooler.html
I was able to speak with an engineer and he suggested this cooler and their MHX-530 for my application right off the bat. He understood that a rotary is a unique situation. He was able to give me hard data regarding pressure loss and flow rates. So I bought the most expensive cooler because sometimes, that is what you do.
Last weekend I got to test it in 94-95 degree weather on the slowest road course I have ever been on. I thought it did well considering the conditions. Oil temps were 220 and water was 200. There was no oil pressure loss over any of the other coolers I have run to date. To accurately judge the cooler, the race track has to be taken into consideration. It is the new 2.0 mile configuration of the World Wide Technologies Raceway (AKA Gateway International) in Madison, IL. The new layout features 4 (YES 4) first gear turns and allot if track sections that I could run in 2nd. This means high RPMs at low ground speed = low air speed through the cooling system.
Is it better than 2 OE Mazda coolers plumbed in parallel? Yes if only because the plumbing is SO MUCH simpler. Also this is a brand new US Made oil cooler and not a 30-40yr part that might still be good but is destined to leak in the future.
As far as the OE knock offs are concerned, there are too many unanswered questions like how are the tubes constructed, is the double pass baffle installed so that it doesn't leak, who makes them, etc.
Last edited by mustanghammer; 06-21-21 at 05:51 PM.
That is an interesting design. I am obviously missing something, because I can't figure out the oil flow path to give it 3 passes or even to use the entire cooler. I am sure it must be, it is just not obvious. Having it in hand (or in car) can you describe the path the oil follows. Unless each header is also divided lengthwise?
The flow is from the bottom. The oil travels 1/3 of the lower tank, then goes up over across the top tank to the 2/3 spot, then down where it goes back up to the top and out a tube that runs through the top tank. The cooler is based on a direct fit C6 Corvette application.
I had to swallow hard when I paid for it. But if you factor the cost of two quality coolers, the fittings and the hose that is required it isn't that expensive. The famous racer paid $1000 for a custom built Fluidyne so I didn't feel that bad.
Last edited by mustanghammer; 06-21-21 at 08:12 PM.
Cool solution to what I assume must have been a packaging problem on the Corvette. It also looks like it is a low pressure drop design (or high flow design), since there are15 tubes per pass, rather than 3 and 4 for the stock RX7 coolers.
I have just been going through the high oil temperature problem on my car. Just finishing up the modifications and will hopefully be able to test in hot conditions (seems pretty easy in SoCal these days) in a couple of weeks. I was at Auto Club Speedway a little over a week ago. Oil temp was creeping up to 265 degF, while water was solid at 190 (air temp was around 95). Turns out part of the problem was my oil temp gauge was reading at least 20 degF high on the top end. Seems that the sender and gauge were not quite calibrated together. I managed to get water to boil at 230 degF according to the gauge in the car! :-) I did some more testing on the kitchen stove with corn oil (and my wife off at the movies with friends) to confirm the miscalibration. A 20 ohm resistor in series with the sender will give me accurate temperature in the 210 to 265 degF range. It will read low at lower temps, but I don't really care there. I am hoping that relocating the oil cooler to minimize air bypassing will pick up the rest of the improvement that I need. In the worst case, I may be looking at the Improved Racing cooler you have.
What helped my high oil temps was running 2 FC coolers. My instillation is not ideal with one cooler in front of the other, but the plumbing was reasonably simplified by mounting one with the ports up and the other with the ports down. It made a big difference in the oil temps, but what is more interesting is that it improved the oil pressure by about 15psi when the oil was hot.
Steve Eckrich had an idea to use 2 Mazda cores, cut the header tanks off and weld on a single header tank to make it a double thickness stock style cooler, that would be nice and easy to install. That could be a good solution for broken GSL-SE coolers with cracked fitting bosses, they are very thin and notorious for cracking over time.
Did you have any other concerns with the Afco cooler other than the guy not getting back to you? I'm just... on some gut level wanting more cooling area than the Improved Racing cooler and the Afco 80420 price is right.
I had to swallow hard when I paid for it. But if you factor the cost of two quality coolers, the fittings and the hose that is required it isn't that expensive. The famous racer paid $1000 for a custom built Fluidyne so I didn't feel that bad.
interesting. i wouldn't say its cheap, but its less than a new FC cooler...
Did you have any other concerns with the Afco cooler other than the guy not getting back to you? I'm just... on some gut level wanting more cooling area than the Improved Racing cooler and the Afco 80420 price is right.
Size was the main issue for me. I also don't remember seeing an oil capacity and it is not a very thick core. It could be a good choice though and yes the price is right.
As it was, I had a limited amount of time to get a new cooler mounted and the one that fit the space I had still took a few days to get done.
What helped my high oil temps was running 2 FC coolers. My instillation is not ideal with one cooler in front of the other, but the plumbing was reasonably simplified by mounting one with the ports up and the other with the ports down. It made a big difference in the oil temps, but what is more interesting is that it improved the oil pressure by about 15psi when the oil was hot.
Steve Eckrich had an idea to use 2 Mazda cores, cut the header tanks off and weld on a single header tank to make it a double thickness stock style cooler, that would be nice and easy to install. That could be a good solution for broken GSL-SE coolers with cracked fitting bosses, they are very thin and notorious for cracking over time.
If only I had two good OE coolers to work with. At one time I had one from an RX2-3 and one from a GSL/SE plumbed pretty much like yours and they worked great. Of course they both developed core leaks. Charlie Clark has a pair of FC coolers on his EP RX7 and they work great. So, if you got them....run them.
Cool solution to what I assume must have been a packaging problem on the Corvette. It also looks like it is a low pressure drop design (or high flow design), since there are15 tubes per pass, rather than 3 and 4 for the stock RX7 coolers.
I have just been going through the high oil temperature problem on my car. Just finishing up the modifications and will hopefully be able to test in hot conditions (seems pretty easy in SoCal these days) in a couple of weeks. I was at Auto Club Speedway a little over a week ago. Oil temp was creeping up to 265 degF, while water was solid at 190 (air temp was around 95). Turns out part of the problem was my oil temp gauge was reading at least 20 degF high on the top end. Seems that the sender and gauge were not quite calibrated together. I managed to get water to boil at 230 degF according to the gauge in the car! :-) I did some more testing on the kitchen stove with corn oil (and my wife off at the movies with friends) to confirm the miscalibration. A 20 ohm resistor in series with the sender will give me accurate temperature in the 210 to 265 degF range. It will read low at lower temps, but I don't really care there. I am hoping that relocating the oil cooler to minimize air bypassing will pick up the rest of the improvement that I need. In the worst case, I may be looking at the Improved Racing cooler you have.
Carl
Carl
If you go the Improved Racing route ask them about omitting the long exit tube and the installation of a -10 fitting on the top/end of the tank on the passenger side of the cooler. Might make it an even better cooler. Again.....time was my enemy trying to get ready for the race at St Louis.
Took a quick look at the surface area of the OEM and MHX-245 coolers. Not including fin surface (fin pitch looks similar for both units) the MHX-245 was 17% bigger at 678 sq-in vs 580 sq-in for the OEM cooler. Seems like a useful improvement, backed up by on track performance.
Mark, are your coolers connected in parallel or series? It looks like there is a tee at the top right. Also, where do you measure the oil pressure? If at the oil filter base, (and the coolers are in parallel) it makes sense that the idle oil pressure when hot (or cold for that matter) would be higher, since less pressure drop through the coolers. I wouldn't think it would make a significant difference at higher RPM though, since I would expect the rear pressure regulator to be controlling the pressure at some level (70psi or so stock, probably something higher race prepped). Or maybe the setpoint on your rear pressure regulator is just higher than the pump can put out? I just measured my oil pressure vs RPM and hot or cold, the idle pressure was 30 psi. That increased to 70psi by 3000 rpm and stayed that way to redline. The engine builder decided that the stock rear regulator made sense. I can't remember exactly why. The idle pressure is also some amount lower than it might be otherwise, because the check ***** in eccentric shaft "squirters" were removed to improve oil cooling flow to the rotors (after somehow warping the apex seals on a pretty freshly built engine).
I just installed an FC cooler using banjo fittings, but I previously had the first gen cooler (originaly under the short radiator and then out in front of everything when I went to a full length radiator). I repaired the cracked bung by welding the crack and then welding an AN fitting to it. In my mind that totally eliminates the problem of the thin cracking bungs. I think the banjo fittings on the FC cooler probably induce less stress on the bungs as well, although as you point out the bungs are a lot beefier. It also makes routing the hoses a little easier.
Did you have any other concerns with the Afco cooler other than the guy not getting back to you? I'm just... on some gut level wanting more cooling area than the Improved Racing cooler and the Afco 80420 price is right.
That Afco cooler does look interesting, 25X10 with a 1.56 thick core, and -12 fittings seems pretty robust.
I used to have some very high-level contacts at Afco, I can check to see if I can get some more information about the cooler.
Took a quick look at the surface area of the OEM and MHX-245 coolers. Not including fin surface (fin pitch looks similar for both units) the MHX-245 was 17% bigger at 678 sq-in vs 580 sq-in for the OEM cooler. Seems like a useful improvement, backed up by on track performance.
Mark, are your coolers connected in parallel or series? It looks like there is a tee at the top right. Also, where do you measure the oil pressure? If at the oil filter base, (and the coolers are in parallel) it makes sense that the idle oil pressure when hot (or cold for that matter) would be higher, since less pressure drop through the coolers. I wouldn't think it would make a significant difference at higher RPM though, since I would expect the rear pressure regulator to be controlling the pressure at some level (70psi or so stock, probably something higher race prepped). Or maybe the setpoint on your rear pressure regulator is just higher than the pump can put out? I just measured my oil pressure vs RPM and hot or cold, the idle pressure was 30 psi. That increased to 70psi by 3000 rpm and stayed that way to redline. The engine builder decided that the stock rear regulator made sense. I can't remember exactly why. The idle pressure is also some amount lower than it might be otherwise, because the check ***** in eccentric shaft "squirters" were removed to improve oil cooling flow to the rotors (after somehow warping the apex seals on a pretty freshly built engine).
I just installed an FC cooler using banjo fittings, but I previously had the first gen cooler (originaly under the short radiator and then out in front of everything when I went to a full length radiator). I repaired the cracked bung by welding the crack and then welding an AN fitting to it. In my mind that totally eliminates the problem of the thin cracking bungs. I think the banjo fittings on the FC cooler probably induce less stress on the bungs as well, although as you point out the bungs are a lot beefier. It also makes routing the hoses a little easier.
Carl
Well I am Mike, but I am sure you were talking to me LOL
In all of the engine iterations I have run, from stock GSL-SE to an engine making more than 2X that power, I have used the same regulator, and same mechanical oil pressure gauge, the regulator was squished a bit in a press and normally gives us 65-70psi hot oil pressure.
I only started seeing lower pressure when I started making much more power, the worst case was a 24hr in screaming hot August weather, with a cracked header. For good or bad in that race the oil temp gauge was also broken so I didn’t have to see just how hot it was getting.
Once I installed the second cooler the pressure was right back to where it always was, and the oil temp was staying below 240. I am sure that the lower pressure was just from the oil thinning out when it became excessively hot.
Hey Mike! Regarding the locations of your two coolers. If you move the one in the rear up to give it access to fresh air, you will get lower temps. Charlie Clark tried it both ways and "stair stepping" the coolers makes a difference.
I have a Mazdaspeed rear regulator and a shimmed front regulator and cold temps on fresh oil is 90-100PSI. Watching in car video when the car is hot, oil pressure drops with RPMs but pegs back up to 90-100 starting around 6.5K. The Mazdaspeed regulator was one of the few things I was able to salvage from the Prather 12A engine that came with the car in 2002. Seems to be worth it.
One other point, when oil pressures get high, I think it is a good idea to look at the burst pressure ratings on the oil filter. I run the K@N Silver filters (the cheap ones without the nut) because they have a thicker can. I get them from Summit Racing when I am trying to fluff up an order to get free shipping.
So this feels like a dumb question but where are you all taking the oil temp reading from? What kind of sender? We had an Autometer sender/gauge plumbed into the side oil pressure port and oil temp there was always really low, like below 180. That's running a GSL-SE under radiator cooler. Now I'm wondering if we just have a super effective cooler or were we just running the sensor in the totally wrong spot? We are currently not running an oil temp gauge as our adapter at the pressure port made for an overly long attachment that was prone to failure.
My oil temp and oil pressure gauges are mounted to a block sandwiched between the block and oil filter adapter. It may not be ideal, but I believe this arrangement is very common on rotaries.
All this talk of multiple or upgraded coolers, is only an issue when you start making a lot more power than a stock rotary. These engines are over 200hp at the wheels when extra oil cooling becomes a problem, if you have a relatively stock engine it very well may be running just fine at 180. Also, stock engine management runs ridiculously rich at wot so there is a lot of extra cooling from running so rich.
Thank you Mike. We are now running a street ported 6port motor that should be making around 200hp we think. We are running a Webber 48ida that does run rich at WOT so maybe that's helping. We do have an available port on our oil filter block so maybe I will hook that gauge back up...
I read oil temps and pressure from the same kind of adapter block shown in the previous post. I use mech. gauges only.
In my case I am dealing with the extra HP of a ported engine in combination with a close ratio 4spd transmission that keeps RPMs constantly above 6K RPMs if the car is being driven hard. This all adds up to a need for better than stock cooling everywhere.
05-24-21, 11:08 AM
