Cooling problems with undertrays?

[fanamingo]

I'm working on an undertray for my car and have come up with some cooling questions for anyone that knows about such things. Both my oil pan and transmission case are aluminum and extend down slightly into the airflow beneath the car. Could blocking with an undertray cause any overheating? The oil temp would be somewhat moderated by the fact that the engine itself is cooled via the radiator. The transmission has an ATF "warmer" that has coolant hoses running to it, but I don't know if it also helps cool the transmission. The "warmer" has two warmer and two bypass hoses running to it, and I've no idea how it functions.

I may be able to tap into the ATF temp sensor with a multimeter, but this will only give me a voltage reading. I wont' have a good idea of how that reading correlates with temperature.

[diesel_john]

Yes, one does have to watch temperatures. I have gotten my oil so hot that it caused the rear main seal to leak. But that was a 95 degree day.

[TestDrive]

On a warm day and a long trip, ATF gets hotter than engine coolant. This fact is derived from working in a service station back in the 1970's. eg. Car Owner: "Fill her up and check the oil." ... Me: "The oil iis a quart low, Sir. And it looks like it's due for a change." Car Owner: "Yeah, I should have changed it before I left, .... How long for an oil change." "We're almost done with the one in the first bay. Should be less than 1/2 hour." With the car on the hoist, the transmissions were always obviously physically hotter than the radiator.

FWIW. In the 1980 I operated a specialized 6x6 20 ton vibroseis truck with automatic transmission. On 100F air temp days, the transmission oil temp ran around 280F-290F. Engine oil temp ran about 220F. Engine coolant temp ran around 200F.

[lunarhighway]

although my undertray doesn't cover the oil pan and the exhaust it would mostely shield it from any direct airflow, because i didn't want to risk anything and because the exhaust would contact the undertray i made a cutout in the trailing edge of the tray to give them both some breathing space....haven't noticed any problems with overheating and such.



i might get away with better aero, but i wouldn't want to find out my mods cause trouble if i'm on holiday for example and my driving is a bit more demanding than on my dayly commute

o the other hand i've wondered if an aluminum undertray wouldn't actually function as an heatsink and improve cooling. if you do a full undertray you might also consider louvers below the parts you want to keep cool they will actually extract hot air at speed

[Christ]

If your tranny and oil pans stick out into the air stream, sacrifice the extra bit of airflow, and clearance your undertray for them...

If you later decide you'd like to chance it awhile, you can always make some nice scoopy kinda things that cover them up, just make them removable until you're sure they won't have any effect.

IF either has vanes on it, it's designed to help cool, end of story. That doesn't mean its' actually necessary, but that's the intention. With Honda cars, it's pretty common that they have more cooling capacity than necessary, especially if you're only using it as a DD and not really working it out.

BTW, temp gauges are cheap... and trans temp gauges arent that expensive either... might be a good investment if you're worried about your trans.

[CobraBall]

"Most ATF can withstand normal operating temperatures of around 200 degrees F for tens of thousands of miles. But if the temperature of the fluid rises above 220 degrees F the fluid starts to break down quickly. Above 300 degrees, fluid life is measured in hundreds, not thousands of miles. And above 400 degrees, the fluid can self-destruct in 20 to 30 minutes!"

Also above 175 degrees ATF life is cut in one half.

You may ask "why the radiator/ATF warmer?"

ATF (depending on individual Brookfield Viscosity rating) can become ineffective at extremely cold temperatures.

If in doubt, a transmission fluid temperature gauge sender can be TEE-ed off the transmission-to-radiator line.
Installing a Transmission Temperature Gauge

[Christ]

I've never seen an ATF warmer... always coolers, where the lines are put into a secondary radiator that is held to or near the radiator, or a part of the radiator...

Those were always used to keep the ATF cooler though, since the engine's coolant doesn't usually go much over 200* (sarcasm) I believe the average thermostat is 190*, correct?

[never stock]

Many Honda's use a warmer/cooler. The warmer/cooler uses engine coolant to warm the atf at low temps, once the engine & trans are at runnig temp the warmer then will act as a cooler.

Tim

[minAirForce]

This is a great idea. I thought about doing this to my project.