Adding transmission oil cooler

How much do you want to tow? What would call for the extra cooling capacity?

No need if you are towing an ultralight trailer and a couple hundred pounds.

 

i would be more worried about the inverter coolant being cooled.

i waited to change the psd fluid and there really wasn't any missing. i've loaded down my car with people and camping gear (heavy stuff... even cast iron pans) for trips around 3,000 miles.

i've towed cars on several occasions more than 30 miles.. some over 3500 ft gains through the mountains.

i'd also worry more about the ICE oil being cooled. if i tow things or i'm going on long trips, i need to add oil.

 

I've been trying to figure it out for a 2006. I doubt that the existing oil pump is adequate to feed the extra plumbing to a radiator even if there were a place to attach the lines. The best I've come up with so far is to run a line from the drain plug to a pump, on to a small radiator, and back to the fill plug. The pump at Remco lube pump repair parts | replacement parts for Remco products is designed to lube an automatic transmission while pulling the car (wheels down) behind an RV. It might do the job. The extra plumbing from the drain plug is going to be exposed, and I'd feel a lot happier if there were a skid plate protecting it. Any other ideas?

 

Perhaps the first step is to monitor and measure the oil temperature:


03 Prius Transaxle Temperatures

First make measurements showing there is a problem:


Bob Wilson

 

Bob,

Could you make an educated WAG about the value of a transmission cooler on a Gen2/Gen3? Assume towing 1600 lbs uphill at maximum power long enough to exhaust the traction battery capacity (there are such reports). My assumption is that this is just so far beyond the design specs of the standard system that something is going to overheat. Standard towing packages generally include a transmission cooler, and perhaps a larger engine radiator. Now maybe MG1 will fry before anything else, but some extra transmission cooling sure sounds like a good idea to me!

Would Mg1/MG2 temps be a useful proxy for oil temp?

 

The first step is instrumentation and testing in controlled environments. This replaces guesses with facts and data.

You might start by reading some of the Dept. of Energy reports on the NHW20 transmission. They pretty well studied the heat transfer characteristics. Google will return the links.

Those are key power units and I would recommend keeping them under 100C. The oil helps cool them as well as providing lubrication. We don't know the exact failure point of the 'potting' plastic although the Dept. of Energy reports suggest it is higher than 100C. Just I'm conservative and prefer to keep MG1 and MG2 under 100C. When they reach 95C, I begin to soften the power applied.

Bob Wilson

 

One of the what? My 2006 doesn't have any transmission oil lines, and I doubt that the 2010 does. That's why I thought up the jury-rig method of modifying the drain/fill plugs as a way of accessing the oil. An oil cooler is cheap, but a pump to move the oil is considerably more.

 

I'll accept that as a usable WAG

Now I just have to figure out how to read MG1/MG2 temps on a Gen2. Apparently it's known on Gen1/Gen3, but I haven't seen any xgauges for MG temps on a Gen2. Anybody?

 

Perhaps you might start with buying the Toyota maintenance manual(s). I would recommend Volume 2 that covers the major systems including transmission.

Bob Wilson

 

Just in case you guys weren't aware, the transmission fluid is already liquid cooled by the inverter coolant and radiator.

Just another idea if that's not enough; perhaps simply increase airflow to the existing inverter/transmission coolant radiator with an extra fan?

 

How so? Is there some sort of heat transfer radiator between the inverter coolant and transmission oil? It would sure be easier to increase the inverter cooling than the transmission oil directly.

 

They have a subscription service that allows access to all of the maintenance data. However, I understand the web interface could be better. I just buy the paper manual and know it works as long as there is light.

Bob Wilson

 

Yes, there is a heat exchanger integrated into to the transmission casing. It is a small labyrinth of coolant channels in the casing, strategically located where a lot of transmission fluid flows past it.

I don't have a drawing handy, but I found a picture of the one from the hybrid Camry in a 2008 report from the U.S. Department of Energy, EVALUATION OF THE 2007 TOYOTA CAMRY HYBRID SYNERGY DRIVE SYSTEM, Prepared by: Oak Ridge National Laboratory. I assume it is similar to the Prius, but no guarantee. (anyone with the right drawing or photo please post!)


(from hybrid Camry, not Prius!)

There is a nice drawing posted by Ken1784 that shows the coolant loop. It goes from the radiator --> inverter --> expansion tank --> pump --> transmission --> radiator.

Image from Ken1784 's Album. ^^


(Caution: There is danger of inverter overheating if air gets trapped in the inverter heat exchanger)

 

I plan on getting a trailer 5x10 cargo from Ga bringing it back to Louisiana It should be raining the day I bring it back and with the cooler weather should keep the temp down. I plan to tow around 55 60 mph tops. If Interstate too fast I will take it on the B route I should not have any issue going 60 trucks do it all the time. I figure if I carry an ice chest full of ice if it gets warm I can dump it on there it should aid it in cooling some.