FM oil cooler

[Magpie]

I'll go through some of my data and post a selection. I have oil temp, RPM, ambient air temps, speed, engine bay temp, EGT's etc that I can use.

[greenMachine]

Watching my oil temps this weekend, idling the car would bring it up to 70 fairly quickly then 80 after a while of sitting still waiting for my run. On the track, warm up lap with some load would lift it to 90 and after 3 full speed laps the max I saw all day was 105 degrees.

I think this is fairly ideal for a track car... I don't know if oil temps would drop below 80 at cruise but I doubt it.

My oil cooler sits 80mm in front of my radiator.

Good data point, but to be useful need to know is this a turbo (ie rwkw?), and what was the ambient.

Oil temp is way more affected by rpm than rwkw..

Hmmm ...

Oil heat, like water heat, is a function of the combustion process converting fuel into heat, and what doesn't go out the exhaust pipe with the combustion gas, mostly goes out through the water and oil. The more power generated, the more waste heat has to be dealt with. Since high power is usually a function of high revs, you are correct as far as it goes. To put is simply, at 8000rpm, there will be twice as much waste heat from a 200rwkw engine as a 100rwkw engine., not the same amount in both. Power might be accompanied by increased revs (almost certainly), but it is the power generated that is key to heat generation.

Managing the oil temp is easy without a thermostat - just blank the cooler airflow off in winter, or when oil temps persistently fall below your minimum operating temperature, the operating range is probably pretty broad so that a precise temperature is not as important as keeping it in the specified range. If it gets too far north, start opening up the cooler. Don't forget to make it part of your track setup checklist though!

[Apu]

A bit more data as I drove Apu to work this morning. Apu is turbo'd so oil temps will be a bit higher.

~20degC in traffic...traveling about 40kmh most of the way.

Oil temp maxed about 105degC - coming off ANZAC Bridge it did creep past 105 as it gets jammed up there. Most of the way in start-stop traffic moving at 40kmh, I was sitting on about 100degC. If it did get to 105degC, a short run to about 60kmh would see the temp drop to 100degC or lower.

I pulled over for petrol and when I restarted, oil temp was 100degC. I decided to see how much I could drop oil temp when I get the water spray fitted, so I trickled about half a cup of water over the oil cooler (which is mounted behind the firewall where the Nopro tank would fit). Oil temps dropped to 95degC whilst pootling along at less than 40kmh. Those who drive past Birkenhead Point in the morning will know what I mean.

More info!

Drove home this evening...probably about 25degC, and took the highway so was able to hit 100kmh for good stretches. Oil temp sat about 80-85degC. Didn't get past 90degC.

[Magpie]

This was with the car being run in last week. The EGT's were around 600 degC
Red - Oil Temp
Green - Water temp
Blue - Engine bay temp
Olive - Ambient temp
Purple - RPM
Grey - Speed


Oil Temp New Head by Eipeip, on Flickr

Lakeside - EGT's were around 700 on track. The only difference in the car is the engine. Both times were with a PWR water/oil cooler combo. Sensors in the same position etc.
Lakeside Oil Temp by Eipeip, on Flickr

[greenMachine]

Interesting Magpie. Thanks for posting.

If I am reading the Lakeside graph correctly, water started moderate, and oil was cool, water climbed quickly and stabilised pretty well, but oil climbed more slowly and kept climbing past the water temp before it peaked and then slowly fell. Water temp behaviour is what I would expect, and the oil temp also until it peaked but can you shed any light on what brought the oil temp and the water temp down - cool down lap?

[Magpie]

Yes cool down lap. You can start to see the engine bay temp start to increase due to heat soak (blue line increasing).

I'll get some more data when in Sydney, hopefully the E85 may make a difference as the EGT's will be a little cooler.

[Dweezle]

Thanks everyone.
All super useful information.

I think my temp issue is due to the near enough 8000rpm.
If I keep it below 7400 I don't seem to get anywhere near as high oil temp.

Highway, I stabilise at about 105.

If I just drive around town I am usually around 85 degrees.

I really like magpies oil cooler incorporated Into the radiator.
Is that a PWR item ?



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[NitroDann]

The oil cooler in radiator is an okay idea, but you are of course simply loading the water cooling system with more heat, and even if it worked to keep the 2 temperatures identical, this is far from ideal, it doesnt just happen that your oil should be the exact same temp as your water, your oil should be the exact same temp the manufacturer has designed it for... So while ignoring the -water is now very hot- issue its still no better than an oil thermostat, or cooler behind the radiator, etc.

In general when I am tryin gto figure out the right way to do something I read the data sheets and manufacturers engineering papers when available, and then I go and look at very high end racecars and see how the pro's do it. In almost every case the Pro's use external adjustable oil pressure regulation and thermostats, dedicated oil heat exchangers, correctly ducted using the 1/3rd opening area rule, and you will find the coolers mounted in every location at every angle and every height relative to the engine (ie a foot above everything on a rear wing mounted 'upside down' is ok).

Dann

[Apu]

I tend to get excited by 2-in-1 products...toaster and kettle, remote controls (damn you Logitech!)...but somewhere down the road, it always screws me over. One part fails...and you have to replace both.

I don't know how much the radiator / oil cooler combo costs, but my guess is "not cheap". So if you get a hole in one, you'd effectively be replacing three items.

[NitroDann]

yeah its like 1200 dollars for a radiator and an oil cooler.

[Apu]

That's nearly double the cost of buying both items!

[Magpie]

Yes it is the PWR item. Yes it has an oil thermostat as well as external oil pressure control.

Yes there would be heat soak both ways, however as the data shows on the track the two temps are independent. This is also shown in normal road conditions.

The 2 parts are well separated but there is the potential for one part failing and rendering the whole system stuffed. If that ever happens it will be replaced by something similar to make use of the space for the ITB air intake.

Overall I'm happy with the setup.

[rascal]

To put is simply, at 8000rpm, there will be twice as much waste heat from a 200rwkw engine as a 100rwkw engine., not the same amount in both. Power might be accompanied by increased revs (almost certainly), but it is the power generated that is key to heat generation.

I disagree.

Real world example. My daily is a turbo golf. It has an oil temp gauge so I can monitor oil temps as needed. It's maximum power is at 5000rpm, after which power falls away to the cutout at 6700. I can drive at 5000rpm (max power) and the oil temp slowly climbs. If I then sit the revs at 6500 the temp soars, and when I drop the revs back down to 5000 the temp reduces again. So running a higher rpm but lower horsepower heats the oil more than the lower revs but higher horsepower does.

[madjak]

My understanding is that there are two main factors heating oil in an engine.

Temperature from combustion.
Temperature from shearing the oil (friction).

Engine load affects the heat generated via shearing the oil which is a large factor of oil temps in race cars. Temp transfer from the combustion which is linked to rpm depends on how effective the water coolant is and the total engine temp.

This is why you can generate heat in the oiling system at lower revs by loading the car. Also why transmissions like autos get hot whilst towing as they are basically shearing the oil in the torque converter.

In magpies graph the big spike in oil temp is from the shearing which drops rapidly once the engine load is dropped during the cool down lap. If it wasn't for the temp caused by shearing friction, oil temp would trend towards engine temp which is pretty close to water temp.

Edit: minor tweaks

[Magpie]

Lets keep this simple.

As RPM increase the volume of air that is consumed and burnt with the fuel increases. This will lead to an increase in the volume of exhaust gas as well as a proportuional increase in temperature (sorry for treading on your toes here Dann).

As an explanation at 8,000 RPM (and 700 EGT) the volume of air increase from 7,200 to 23,344 ltr/min due to combustion. It is possible to claculate the extra heat etc but this is keeping it simple. However drop the RPM (and EGT) down to 5000 and 600 the values change to 4,500 and 13,091 ltr/min.

The engine heating up is a product of RPM, Intake temp, EGT's etc therefore the more RPM the greater the heat increase (simple version). This also explains why having cooler air is important. Using the first example 8,000 RPM (and 700 EGT) by dropping the intake temp down by 7 degC the volume of exhaust gas increases by 2.4%.

Correct me if I'm wrong here Dann but in a turbo engine the EGT's are higher than a normally aspirated engine? If this is the case and EGT's increase to say 900 degC the combined effect would be an increase of 23.4% in exhaust gas flow, just what a turbo needs..

Sample calcs.
RPM____________8,000
Displacement_____1.80
Intake Volume____7,200 ltr/min

Intake Air Temp____27
EGT______________700

Intake Rankine_____540
EGT Rankine______1,752

Ratio Volume Increase_3.24

Exhaust Gas Volume 23,344 ltr/min

Sorry madjack posted at the same time as yours. I have not taken oil friction into account. I can post EGT graphs vs oil temps for discussion if needed.