DrPoke

Several different threads here have talked me into believing that I will eventually need an oil cooler. I already have a remote oil filter mounting kit (https://www.rockauto.com/en/moreinfo...190876&jsn=395). Since it doesn't get hot enough where I am, I'm leaving out the AC and installing a coolant reroute and a 180-degree thermostat. It will eventually get a turbo, with a goal of around 300 HP, but right now it's mostly stock.
I've already pulled the engine to deal with a variety of other issues, but while it's out and I'm ***** deep in it, I'd like to get my various coolings sorted.
Is there any reason I shouldn't use an automatic transmission radiator (car is manual) and use the transmission fluid cooler as an oil cooler?
If I did, I'd run the oil filter just prior to the cooler so that the oil was warm when it was filtered, and relocate the filter to near the radiator.

tomrev

For a car that may be street driven a lot, I would plumb in an oil thermostat before the cooler. Mocal makes a nice one that is fairly inexpensive. I have more experience with Porsche, and Lotus and coolers than Miata, but in my present Lotus Elise, I can't get the oil warm enough on the street, and have gradually removed all the factory coolers, tried a single Earls 19 row, and finally removed even that. I have to beat on it to keep the oil above 180. Track cars will be much different, so it depends on what your plans are. Even then, for a much quicker warm up, I'd add the thermostat. I don't like to work the engine hard before min. of 160 deg. oil temps, so it's important to add an accurate gauge, so you know what's going on. If I didn't have a gauge in the Lotus, I'd see 190 coolant, and think it's OK to start beating her, when in fact the oil isn't even 140 yet. You can get a Mocal therm. in -8 thru -12 inlet sizes for under $100.

DrPoke

Mostly street driven with occasional autoX or track use, but I expect the street driving to be far from gentle.
How would an oil thermostat work if there is not bypass line- or does it just have a hole drilled for that function?

DNMakinson

iTrader: (3)

Look Here

Miata needs at least -10AN lines. I would think XMSN cooler would be much too restrictive.

You can see where / how I mounted mine. I still don’t have my oil temp gauge connected so I have no hard data for you.

tomrev

Most therm. have 4 ports: oil in, cold oil back to engine, warm oil out cooler, and cooled oil returning to engine.

tomrev

When you are making the oil lines up for the cooler, you simply run the first line into the thermostat, then the "out" port to the cooler, from the cooler, a line returns to the "in" port on the therm., and the 4th port goes back into the engine, via the sandwich plate you will use to route the cooler lines. When the engine starts, and oil is cold, it enters the therm., gets routed right back into the engine.( 4th port). As the temp raises, the plunger begins to open, and a little oil starts running to the cooler, allowing the oil to reach temp quicker, as in a stock, cooler-less situation. When hot, say at 180 deg., the therm. is fully, and all oil is routed to the cooler, and back thru to the engine. Most thermostats always pass a little oil thru to the cooler, even when oil is cold, and this tiny flow in my Lotus would never let the temps hit a proper heat range, so in that car I had to fully pull the coolers, and therm. out. In the Porsche's, you could watch the oil quickly warm up past the therm. opening temp point, and then a few minutes later, with the therm. open, it would drop back to the 180 deg. opening point, and stay there. This was on the street; on track, it went up to 215ish, and stayed, whereas before the cooler install, it would just keep climbing, getting hotter and hotter till I was afraid to keep driving. If you can mount a cooler, and learn to make up AN braided lines, it will be simple to make the additional lines to and from, and only add the cost of the extra fittings, and the thermostat. I'd never run an oil cooler on a street car without a thermostat, unless I lived in Death Valley, and ran the **** out of my car on a daily basis.

tyhackman15

I'd keep an eye on oil pressure with that remote filter AND an oil cooler. May have to go back to the factory filter location once you add a cooler.

hornetball

iTrader: (4)

Oil temperature is driven by continuous high RPM. The shear forces from RPM in the main and rod bearings create the temperature -- NOT HP. You need it for track use. Anything else . . . install an oil temperature gauge first to see if it's needed.

Do not use an automatic tranny cooler for this application. Motor oil is much more viscous. You need to feed it with -10AN (5/8") lines and you need good flow + good surface contact area. That costs money.

ATX.

So whats the smallest oil cooler we can run and still get adequate flow? Are those 10 row oil coolers too restrictive?

ryansmoneypit

iTrader: (6)

you cant street drive a 300 hp miata long enough to need an oil cooler, IMO. you will die, or be in jail first.

shuiend

iTrader: (24)

This. I think an oil cooler is overkill for about 90% of the people who turbo a miata. It should be one of the last things you do after boosting and sorting out everything else.

Joe Perez

iTrader: (8)

Both true statements.

When I was younger and foolisher, I thought that I would need an oil cooler on a 225 HP car which was often autox'ed and also driven hard through the desert roads of inland southern California. I installed a plate-style cooler, along with a sandwich type thermostat, at the same time that the turbo was going in.

Now, I'd had the temp gauge in previously, so I had a pretty good idea of what my car's oil temperature looked like in naturally-aspirated operation. After installing the cooler, I found that my oil temp was coming up much more slowly in the mornings. On cold days, it never even got to normal during my morning commute.

Turns out that all oil thermostats have some degree of bypass, and this is sufficient to really screw with your warmup.

In the end, I removed the whole thing and went to an OEM-style water/oil exchanger from a 1.8 engine. This was the ticket, Warmup was now even faster than stock in the mornings, and oil temps never got scary when I was blasting up the side of Palomar Mountain on the weekend.


TL; DR- a car operated on the track, at sustained high RPM, needs an oil cooler. A car with street tires, no matter how much of a bad-*** you think you are ripping around through Mesa Grande for fun, you're probably not generating anywhere near enough heat to make one worthwhile.

DNMakinson

iTrader: (3)

This brings up a thought I had sometime back. On the track (only one weekend so far), I turned boost down to be more gentle on the engine, but then ran 5K+ RPM most all the time.

Would the engine be better off if I ran one gear higher, turned the boost up to compensate, and end up with same acceleration potential but less RPM and less oil heat? I suppose the answer would depend on the FMIC and water cooling strategies, as it all interrelates to some degree (pun not intended).

Anyway, I have the oil cooler already installed, so could well be OK either approach.

Thoughts, anecdotes, opinions (valid ones are best).

hornetball

iTrader: (4)

All of the oil thermostats I've seen are always open to the oil cooler but open up a second, bypass port back to the engine block when cold. Thus, they are failsafe.

Even a 1.6 Spec Miata with 100HP will drive oil temp to 300F+. But the boost will drive water temp as you heat up the head. So, I dunno'. Personally, I'd find it really difficult to control my urge to wind up the engine on track. Especially when chasing down that GT3.

Joe Perez

iTrader: (8)

Man, you're about to get bombarded with opinions. If you're lucky, maybe one of them will come from someone who is an actual mechanical engineer with experience in lubricating films.

This is a sufficiently complex question that I'm not even going to hazard a guess.

DNMakinson

iTrader: (3)

Hornet did me good. I will stay with my present approach. 175HP on track with 7200RPM limit. Conservative; and I will just enjoy that.

Joe Perez

iTrader: (8)

And yet I appear to have found a fairly good answer: https://core.ac.uk/download/pdf/4396460.pdf

The above is a thesis paper written by two MIT mechanical engineering students. It explores the various factors which affect heat rejection into an internal combustion engine, and specifically looks at RPM vs. load. The paper's summary contains the following:

Savington

iTrader: (31)

Correct

Not as correct. The valve springs and pistons/rings contribute more heat than the bearings do.

hornetball

iTrader: (4)

Valve springs? R U serious?

ATX.

in for the truth