I am surprised but i've never seen anyone else around here talking about how the RX-8 OVERCOOLS the oil in cooler conditions with gentle to moderate street driving. i have always used oil temperature gauges on my RX-8s and i almost never get up to "ideal" oil temperatures during street driving, short of 75+ mph cruising on hot summer days. one common piece of evidence is the "oil foam on dipstick" phenomenon, where moisture in the oil fails to get warm enough to bake off in cooler weather. there's a simple solution that i highlight in this video. i think proper oil temperature will help your rx8 run better (including a hair better gas mileage) and last longer by keeping the oil and engine healthier. I've used this solution on both of my RX-8s, which have both gone on to live long lives with good performance and oil pressure. I would NOT use this solution without a functional oil temperature gauge but i believe it might be very helpful to those living in a colder environment.

EDIT: Apparently this is discussed in the UK RX8 owner's club forums, where many owners also experience low oil temps and developed something similar called the "mouse mat mod".

 

I live in Jamaica. I have a 2008 JDM RX-8 with a single oil cooler. I bought a second cooler, but haven't installed it as yet. I live in Jamaica, so its hot. I don't track my oil temps currently. Do you think based on me living in a hot climate and doing a lot of traffic driving , that I should just keep my one cooler or install the 2nd?

 

if you're in jamaica i doubt the second oil cooler will hurt you that much. probably helpful if you do high speed cruising in summer. it's more an issue in climates that get close to freezing, or below.

 

Personally from some experience, even in a very cold climate a stock Rx8 shouldn't see oil temps that low unless theres something wrong with the OEM oil thermostats. I've tested my stock thermostats and they were keeping the bypass open even up well above 200° .

I wouldn't be surprised if there could be a failing thermostat like its stuck and constantly keeping your bypass blocked or something. Oil cooler thermostats should be treated IMO the same manner we treat coolant thermostats, and be replaced at similar milages to one another. There is mechanical movement, therefore a wear and tear item.

That said, below a point the oil does see passive cooling by being in an environment that also has coolant, which cools the block, which means less workload on the coolant to reduce engine temps, and lowering the coolant temps as the rest.

What you highlighted is very cool. It should also be a message to the owner of any Rx8 experiencing the same conditions of either very high or very low to inspect their thermostats.

Sorry, i just figured it would be helpful and a good follow-up video to this one to highlight maintenance advice.

 

Thanks for the feedback. Both my white car and blue car have always behaved the exact same way. i am wondering the chances that BOTH cars had one or more oil cooler thermostats that were already failed when i bought the cars. but on facebook someone else mentioned that they get oil temps fine in cooler weather too. where do you measure oil temp? it might not be the "best" place but i measure at the oil filter with a sandwich plate. if you're just cruising around town in winter neither of my rx8s ever got much temperature.

as a test, i could touch my oil coolers by hand when it's cold to see if they're warm/hot, implying that the thermostat is stuck closed and forcing all of the oil through the cooler (vice letting it bypass). better yet maybe buy an IR gun and measure actual oil cooler temps.

Thanks for the recommendations, i have a few things to test. it's easy enough to pop them out and inspect.

 

FYI.

Not a cost effective solution but Mazda did address this "foam" issue through a TSB in 2006. Mazda calls it a "milky substance" and provided a part to address this. I explored this repair option but decided there was no "real harm" to this issue. My 2004 has 126,000 miles with original engine/owner.

 

If memory serves me right (and someone correct me if I am wrong)

-Post oil cooler temps can be measured using a sandwich plate at the filter pedestal. This is the most commonly used method and can read a little lower sometimes since the coolers already lowered temps but is helpful because you can see if theres something wrong with a cooler and a temp is too high going in. In my personal opinion, this should be fine for most people. Casual driving you may have temps on the low side but with a proper engine oil selected it shouldnt be too much of a concern. You can simply watch the temp and make sure to get it warmer from working the car up to spirited driving if you want/need to with earlier shifts till it warms up further.

-Pre oil cooler temps can be measured using a modified banjo bolt to accommodate a temp sensor being threaded into it either at the banjo on the front of the block or the banjo that goes into the lefthand side oil cooler. This can give good information of engine oil temps that reflect internal engine oil just as its leaving the block and just how hot the system is running within the engine. Many people have pointed out however that engine oil temps can follow engine coolant temps pretty closely, so theoretically measuring the temp of your coolant via a sensor in your upper radiator hose should put you in the ballpark of where your pre-cooled oil temps are.


YES, there is the concern of "milky oil" due to condensation in the system that can occur. Our oil system does see some contact with air, that said it shouldnt see excessive amounts of moisture getting into the system unless its starting to come in from other places (like your cooling system getting moisture into the oil inside the oil pan as an example). In most cases any slight milky appearance is nothing of significant concern, and once at a proper temp should evaporate out and make its way up and out the oil neck either into the intake (where it can gum up valves) or a dedicated oil catch can either recirc or vented to atmosphere. If there is an excessive amount of that milky foam, the engine should be inspected and it might not hurt to send some oil off for testing to check for any contaminants like coolant or fuel in the oil which would point to other engine concerns.

 

thanks for sharing! i think this eliminates the symptoms of oil overcooling but doesn't address the real issue.

126k miles is no joke - good luck continuing to rack up the miles!