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I have Scotts oil cooler kit, but my oil is running too cold I think. Around 150F while cruising, measured at the oil filter (which I believe is after the oil has been cooled). I am confused because allegedly these oil coolers have a 175F thermostat, but it never gets up that high unless it's summer time and the temperatures are very high outside. I don't know if I have a thermostat failure or what... I replaced my coolant thermostat with an OEM temperature one, which brought coolant up to around 165F, which is better than the 150F it was before. But it didn't do much to increase oil temperature, at least not enough.
It's my understanding that 150F is too low for oil to lubricate efficiently, I was considering blocking off one oil cooler, or maybe half of both oil coolers. I'm not sure if it matters, or which solution is best.
The thermostat is on the hot side of the cooler so logically 150 measured on the cold side should make 175 or more on the hot side. Definitely wouldn't block off coolers based on this information. Your engine and all fluids inside it are at ECU indicated coolant temp in most situations.
The thermostat is on the hot side of the cooler so logically 150 measured on the cold side should make 175 or more on the hot side. Definitely wouldn't block off coolers based on this information. Your engine and all fluids inside it are at ECU indicated coolant temp in most situations.
Where are you measuring coolant temp?
Coolant temp is being measured at the heater core, the most accurate spot for it afaik. I'm just having a hard time understanding oil temps are 40-50 degrees hotter in the engine than the oil pedestal.
I mean the pedestal sees oil that hasn't been in the engine yet since it was cooled so... What temperature would you expect it to have?
I don't know about the heater core being the most accurate, why not simply read OBD which is read from where the thermostat is located directly in the hot side coolant exit?
The heater setting, the exact location on the heater core (before or after the core?) and the long run of pipe to get to the core would all give you a different temperature reading than what's in the engine. 10F loss for 3 feet of pipe is not even that much.
I mean the pedestal sees oil that hasn't been in the engine yet since it was cooled so... What temperature would you expect it to have?
I don't know about the heater core being the most accurate, why not simply read OBD which is read from where the thermostat is located directly in the hot side coolant exit?
The heater setting, the exact location on the heater core (before or after the core?) and the long run of pipe to get to the core would all give you a different temperature reading than what's in the engine. 10F loss for 3 feet of pipe is not even that much.
I read somewhere years back that the heater core is the best due to coming straight off the engine and it's always flowing, whether the thermostat is open or not. I could be wrong, but it makes sense to me. It's why I chose that location to monitor temps from. And it's reading about 165 under full load, and around 160 cruising, and this is after installing an OEM temp thermostat and removing the colder one that I got from mazmart.
As far as expecting certain temps, I would expect oil to be closer to the ideal temperature, around 165-175, or even higher. I'd be happy with 185. Cold oil doesn't lubricate as well, nor does it burn off condensation.
I'd compare what your heater core gauge reads to what OBD says. The built in temp sensor is immediately in the thermostat housing for the reasons you described. I don't think an rx8 is capable of maintaining 165F coolant at full load even if there was no thermostat at all, so your gauge is misleading you IMO.
For the oil: you really want to measure the hot side to draw any conclusions. That 150F cooled oil will get up to proper temp pretty quick once inside the engine. If it came in at near engine temp, the engine wouldn't be able to transfer any heat to it, making the coolers useless. You can get a used oil analysis to see how your oil is holding moisture, fuel, depleting additives and potentially indicate bearing problems. What you don't want is to block off coolers and have oil temp higher than normal, based on a misleading gauge reading, and compromise your oil life and lubrication when it's warm.
I'd compare what your heater core gauge reads to what OBD says. The built in temp sensor is immediately in the thermostat housing for the reasons you described. I don't think an rx8 is capable of maintaining 165F coolant at full load even if there was no thermostat at all, so your gauge is misleading you IMO.
For the oil: you really want to measure the hot side to draw any conclusions. That 150F cooled oil will get up to proper temp pretty quick once inside the engine. If it came in at near engine temp, the engine wouldn't be able to transfer any heat to it, making the coolers useless. You can get a used oil analysis to see how your oil is holding moisture, fuel, depleting additives and potentially indicate bearing problems. What you don't want is to block off coolers and have oil temp higher than normal, based on a misleading gauge reading, and compromise your oil life and lubrication when it's warm.
I shouldn't have said "full load" I mean cruising at highway speeds, 65-85 MPH, I'm getting 165 at the heater core. It will go higher for a brief amount of time if I'm getting higher in revolutions and really giving it the beans.
I get what you are saying, but it's not an OEM radiator. It's a ron davis style dual pass radiator. The oil coolers are not factory either, they are much bigger. I guess I should have led with that. These oil coolers don't have the 10 or 11 rows the OEM ones do, they have 23.
But I do recognize what you are saying. I am not measuring it at the hottest point. I don't currently possess a way to read OBD2 data, I have a code scanner but I don't think it has the functionality to read live data.
Well I blocked off one oil cooler and it made... pretty much no difference at all. Still hovering around 150 F at cruising speeds, with 37 F ambient temperature. Oh well, I don't really feel comfortable blocking off both, I've got some very hilly areas I have to climb on this trip I'm about to embark on. But I did take note of when the radiator fan kicked on at idle, which is supposed to be around 205 F, and my gauge is reading 195 F when this occurs. So one could assume if the temperature difference is constant, that instead of being around 165 degrees at highway speeds, it's closer to 175. Which is colder than ideal, but acceptable.
I think in due time I will try to take oil temperature from somewhere other than the sandwich plate, as I'm not sure measuring temp there is all that useful.
Last edited by Killawatts; 01-07-2024 at 10:29 PM.
if the cooler t-stats are working then it means little/no oil is passing through the cooler and as a result blocking them off accomplishes nada
try blocking off half the radiator instead maybe …
or as I suggested on here before, get rid of and block off the crappy oil cooler t-stats and install a proper t-stat (with or without an integral remote oil filter) between the two engine oil cooler lines at the engine, with a temp sensor on the line going back to the rear iron pedestal, and it should then be regulating whatever the t-stat temp is there instead.
Which doing it this way bypasses the entire oil cooler line loop completely. This not only reduces the pressure drop of that oil cooler line loop, but eliminates it from acting as a heat loss source as well that might be contributing to low temp.
but even then, if the oil is still not getting up to temp then blocking the radiator in some fashion is the only other choice. Because the load on it has to increase to the point that energy will need to be transferred to the oil as well.
If the coolant t-stat is barely open, the coolant discharge temp exiting the engine may be at the t-stat temp rating, but the coolant temp entering the engine from the radiator could be dead cold and cooling off whatever is bypassing the radiator back into the engine.
In summary, if the heat loading in general is vey low, there likely is a differential temp from the coolant entering the engine to what is discharging from the engine, rather than it being the same temperature all the way from inlet to outlet. This, along with the air inlet temp being low into the engine, is going to result in less energy being transferred into the oil system.
Or at least that’s what my sad excuse of a man assessment today is vs. the past …
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The heater loop for me was a bad place to take temp. It has a very high and not proportional delta from the OBD, the higher the ambient and the higher the power, the worse it was. It was so wonky I tried 2 different gauges/senders, to rule that out. RB had no answer, saying it was inaccurate, but acceptably so. I thought differently, and use OBD temp only. There is no other good way to get accuracy on the Renesis in my opinion.
The stock oil coolers maintain 180 in 30 degree temps here in AZ, with FD thermostats in place of factory. Never had an issue overcooling. Temp taken at oil output line, so sump pickup was less, but not by much. Warmup was quick also, I could see thermostat action on the gauge. You may have a thermostat or gauge issue. I think if you were able to read OBD, you might find your coolant is too cool, and that is actually your problem.
Hope that helps.
Last edited by kevink0000; 01-08-2024 at 04:02 PM.
The heater loop for me was a bad place to take temp. It has a very high and not proportional delta from the OBD, the higher the ambient and the higher the power, the worse it was. It was so wonky I tried 2 different gauges/senders, to rule that out. RB had no answer, saying it was inaccurate, but acceptably so. I thought differently, and use OBD temp only. There is no other good way to get accuracy on the Renesis in my opinion.
The stock oil coolers maintain 180 in 30 degree temps here in AZ, with FD thermostats in place of factory. Never had an issue overcooling. Temp taken at oil output line, so sump pickup was less, but not by much. Warmup was quick also, I could see thermostat action on the gauge. You may have a thermostat or gauge issue. I think if you were able to read OBD, you might find your coolant is too cool, and that is actually your problem.
Hope that helps.
Yeah that's interesting, because in theory the heater core should be a great place to measure temperature. And based on when the fan engages, my gauges are actually reading about 10 degrees lower than ECU indicated temperature. That could be an issue with the gauge itself or the sensor, or the location, who knows.
As far as the oil coolers go, there's too many variables at play for me to know what exactly is going on. It's no longer a factory set up, even all the stainless lines have some effect as a heat sink. And measuring from the cold side is just not all that useful. But to be fair, I'm not sure oil temperature in general is all that useful of a measurement....oil can get really, really hot and be just fine. Oil pressure and coolant temperature seem to be the key ones.
Assuming the oil temperature is also higher in the engine than being indicated (which should definitely be the case due to where it is being measured), I should be around 165-175 oil temps now, which I think is fine.
I ordered an OBD dongle and will pull data from that to find out what the ECU is seeing in due time.
You wanna measure oil temp, measure it at its hottest. Which happens to be a pain to do because that would be in the pan, somewhere close to the main return passge out of the rotors. I've been through this... but with you running diff. oil coolers with god knows what thermostats if any at all, there's no telling.
it will likely be just as hot on the engine discharge line, which is immediately after the oil pump spitting it out of the pan … since it already has aftermarket braided hoses then install an AN adapter between the engine discharge fitting and the hose end fitting. It doesn’t get any easier for adding a sensor.
saw another comment that needs clarifying; the coolant going from the water pump to the heater core hose discharge pipe on the LH side of the rear iron is only traveling 1/2 way through the engine to that point. Rather than traveling all the way back up to the front where the coolant temp sensor and coolant t-stat are. So the temp going to the heater core is most certainly lower than the coolant temp sensor is indicating.
I found it to be sometimes hotter and sometimes colder that the OBD ECT. Under power in AZ temps, it got a lot hotter. At 210 ECT it was showing almost 250 IIRC. More than 240 anyway.
But definitely not biased to cold. That is the hottest side of the coolant flow.
Last edited by kevink0000; 01-12-2024 at 03:39 PM.
I could be assuming too much. Seeing that I never actually attempted to physically verify how those flow paths are configured. Having only seen and trusted various diagrams as posted above. And also assuming there aren’t other issues like combustion gasses getting past seals or other irregularities. Because it does appear in the diagram to quench the induction and combustion/spark plug side first. Possibly I hadn’t considered that it may actually be hotter there and then distributing that heat to cooler parts of the engine. My expectation being that it’d be hotter on the combustion cycle proceeding to the exhaust cycle. Which is shown in the diagram above to be on the return path back to the thermostat.
I just happen to have a full set of new REW irons and housings sitting here though. I’ll try to take a look at them to see how those flow paths are established. I’m curious now …
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My understanding was that the hot side heated coolant then went to the cooler side to try to equalize temps within the keg. The rear iron being the hottest single part of the engine coolant flow.
your understanding doesn’t jive with the flow direction arrows on the keg coolant diagram posted above, which comes directly from the Mazda literature.
Because as you describe it, if it were true then coolant would be heating up the intake compression cycle side of the keg
the diagram shows the cooler coolant being sent down that side instead to the supply pipe for the heater core and then coming back along the combustion and exhaust cycle side of the keg to the t-stat. Which goes back to my post suggesting the heater core temp would be lower than the t-stat discharge temp.
but I’m going to verify this on the iron plates …
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That’s exactly how I understood it to work. The unwanted heating of the intake took a back seat to the constraints of the metal, since there is such a big temperature delta in a small area of aluminum on rotaries.
Plus, all heater loops I have seen on cars I have worked on, have the tap located in the hottest part of the system or the most convenient/hottest part of the system. This is why, I believe, the heater tap is on the LH side, ( not because of JDM RH drive).
Last edited by kevink0000; 01-15-2024 at 05:04 AM.
01-07-2024, 05:48 PM
