My race engine builder was very forceful in telling me to keep the revs and throttle opening down until 80*c. In cold weather (~0*c) with no oil cooler that took forever, and sometimes wouldn't happen without breaking that limit. I then installed a laminova oil/water heat exchanger, which worked well to bring the oil up to temperature, and then stabilise it - without needing another oil cooler to keep the maxT under control. I haven't managed to find a way to fit one to the new car yet, so the best I can do is fit a conventional cooler behind the radiator. That will be much less effective than the laminova in stabilising the temperature, so I'll see how it goes - hence the need to monitor temperature.

No surprise I guess, but your thermostat's 170*f setting is pretty much my engine builder's 80*c.

The oil pump adds more heat to the oil than any other component in the engine. Measuring at a sandwich plate is a fool's errand. Measure at the sump or don't bother.

While I've seen no data to substantiate the claim that the oil pump adds more heat to the oil than any other part of the engine (and have doubts as to whether this is accurate), if this were true, then wouldn't it make sense to measure oil temperature after the oil pump? It is, after all, peak oil temperature which is of most interest.

It would, if the industry did it that way. They do not. They measure it at the sump, so you (the royal "you") should also measure it at the sump, since at the end of the day, the goal is to determine whether or not the measured oil temp in one particular system is acceptable as compared to generally defined industry standards.

e: As far as that claim, it comes straight from an oil engineer who cut his teeth inside JGR's NASCAR engines program, and who now works for Driven, which is JGR's retail oil sales company. Oil pumps contribute the most heat to the system, valve springs contribute the 2nd most, and pistons are third. He described testing rigs where they would spin a bare cylinder head up to speed with no bottom end attached, and hook an oiling system to it, and the oil in that system would reach 180 degrees with no combustion heat whatsoever.

I spent like 30-40min talking with the guy at PRI last year. The main takeaway I got was that oil is fucking weird.

I'd love to see some documentation on this.

Mostly because it's the kind of claim that seems to make a lot of sense if you know a little bit about fluid dynamics, but starts to make less sense as you know more about fluid dynamics. (I'll admit that it's one of those things that might start to make more sense as you get into PhD-level fluid dynamics, because physics can be weird.)

On the one hand, it seems to make sense because the oil pumps is, of course, pressurizing the oil. And we all know that when you compress a fluid, it gets got. This is how air conditioners work, it's why forced induction engines have intercoolers, it's why tire-inflation pumps get hot, etc.

Except that, like most liquids, oil is incomprehensible.

What is it about the oil pump, specifically, that causes it to put more heat into the oil than all of the bearing surfaces and piston rings?

The source is Lake Speed, Jr. You can google his resume. While I can appreciate skepticism of information that does not appear to be obvious on its face, I am not the kind of asshole who questions people like that when they tell me things that directly relate to their area of expertise. :party:

e: -4 props for sharing info about oil provided to me by the R&D director of a NASCAR team's lubrication division. Did I stumble onto Facebook?

If I had to hazard a guess, it's not the actual compression of the oil, because oil doesn't compress (yeah, yeah, I know it does, just not an amount worth caring about), but the shearing effects within the various interfaces of the engine.

Yeah but. Do you vacuum down your oil?

Oil pump is positive displacement with excess oil being throttled through the relief valve, at higher and higher pressure relative to RPM. Possibly that is a contributor.

Turbo is also a contributor that would not come into play on NASCAR - only testing, if that were the case.

Re: Sensor in change plug. This is done on occasion and I have not heard of damage from any that have used that method.

This discussion fits well into the other one on coolers.

If Sav's informant is correct, then yes it is more important (for accuracy, not necessarily for outcomes) to measure T in the sump. For the health of our engines, we are interested in how the oil performs inside the oil passages/bearings/rubbing surfaces. That requires the oil entering the engine to be above the minimum operating temperature, and exiting below the maximum operating temperature. Lets hypothesise that this is an 80-120*c range. So we want the sump T below 120*.

It doesn't matter (probably within certain limits) how high the oil pump pushes the T above 120, providing the oil cooler can bring it below 120, hopefully closer to 80*, to provide a margin sufficient for the oil to be heated to no more than 120* by the time it enters the sump after doing its lubrication thing. Assuming that the excess T above 120* does not do irreversible damage to the oil's lubrication qualities.

Placement of the oil temperature sensor would be less important if the post-oil-pump T never exceeded 120* (or whatever the max operating T of the oil), as that would mean the sump T was less than 120*. However that also means that regulating oil T on the basis of post-pump T would also be safe, perhaps even 'safer', given the sump T is lower than the post-pump reading.

I gave you a :likecat: to try to combat what I admit is a bit of BS behavior here.

I'm still having difficulty with this concept, though. Beyond the simple fact that the mechanism of action for the oil pump putting a large amount of heat into the oil is non-obvious, I keep coming back to the physical properties of the oil pump itself.

It's not very stout, quite frankly. Those gears are sinstered metal, and not large.


I've been trying to pin down exact numbers here, based on the known thermal efficiencies of gasoline engines, the various ways in which "lost" heat energy is transmitted, etc. The problem is that I can't find any meaningful data on the horsepower consumption of an oil pump. We're all familiar with the parasitic crankshaft loss imposed by a supercharger, and the same basic mechanism of action is at work here. For the oil pump to be dong its thing, it must be taking energy from the crankshaft and converting it into a combination of useful work (pumping oil) and waste heat. And the number I can't seem to come up with is how many HP would have to be going into that fragile little gear, and being lost within it, in order to produce a greater amount of heating than the crank bearings, the piston rings, the valvetrain, etc. But it can't be a small number.



I'm familiar with Mr. Speed, and googling "Lake Speed" "oil pump" has thus far returned a bunch of his talking about why his company's oil is the best you can buy, and not a single reference to oil pumps being the largest contributor of heat to the oiling system. I'm not saying that I doubt you heard this, merely that this is one of those concepts which is so far removed from the obvious that it begs for a citation.

I'd also like to see documentation, simply because this sounds interesting, i like to read, and previously on this forum we've hammered home "Miatas are special and not-Miata DPE doesn't matter." Hopefully that doesn't make me an asshole. :giggle:

I'm surprised that the pump puts the most heat into the oil. A pump that size cant draw more than 2 hp, and at worse must be 60% efficient, so at most its going to be putting 0.8HP worth of heat into the oil, that's like 600 watts. That doesnt seem like it would be the largest source of heat for the oil in the engine.

For that drain pul that someone drilled and tapped for the sensor, you know you can just buy a drain plug already setup like that.

Just as a data point for the earlier post about sender location; on my Lotus, which ran much too cool because of the twin stock coolers in the nose, I had first put the sender in the sandwich plate. When the temps were so cool, I doubted the accuracy of that location, so moved it to the lower part of the sump, and got exactly the same temps. At least in this instance, it didn't seem to matter, so for many, who will not have the engine out, or pan off to weld a bung, but do want to begin monitoring oil temps, the easy sandwich plate location probably makes sense.

Thank you!

This thread had gotten me to trying to remember where I mounted the temp sensor back in 2006 when I was just starting into the '92 build. That was it. I found an adapter that was M14-1.5 male x 1/* NPT female. Just do a Google search. Beware that many (most?) of these fittings don't have the flange around the large end, and will thus leak. I thus wound up drilling and tapping an OEM plug.

It was slightly annoying, as you had to unscrew the sensor wire before pulling the plug to drain the oil. After after about two years, something hit it while I was driving on a rough road and broke the stud off of the sensor. Fortunately, the oil stayed in the engine.

I've been searching back through historical photos trying to find a picture of that install. This is the first photo I found showing the gauge in place, but I can't find a picture anywhere near it showing the sensor itself.

https://cimg1.ibsrv.net/gimg/www.mia...013928f98f.png

That photo (and those around it) brought back some good memories. I really loved that car. And also living in Carlsbad, CA, where I really got to stretch its legs.

No arguments there. I didn't spend a whole lot of time doubting him, mostly for the aforementioned "don't look a gift horse in the mouth", but also because right after he said that, he told me the bit about the valve spring testing, and I spent most of our chat trying to wrap my head around that.

In a Fermi-esque way, I would start by figuring out how much oil volume a normal Miata pump is designed to move (or really any gerotor pump, or in absence of that data, any engine oil pump at all), and then look to either the beverage industry (soda/beer/cider) or maybe the petroleum industry for a similar pump with a raw horsepower rating.

Joe, so you’re comment about the sensor being damaged WAS anecdotal, NOT conjecture.

Nice pic.

I'm imagining a thicker oil creating more heat. There's got to be a trade-off between film strength for protection and oil thickness causing drag and heat.

What's wrong with measuring something at its hottest point? If your gauge never goes above 250 or so in the sandwich plate, would it not be safe to say the pan will be the same or cooler? Seems like the same idea as measuring the coolant temp near/in the cylinder head vs in the radiator or something along those lines. Just thinking out loud a bit.

Correct. Thicker oil will run hotter than thinner oil. Too thick and it's entirely feasible to push the oil to a point where a hot 20w50 may not work as well as a cooler-running 10w30, for instance. Ergo, it's best to run the thinnest oil you can get away with given your bearing clearances. I run 10w30 in stock engines and 15w50 in built engines (specifically, in any engine with a non-stock bearing package).