I am having a transmission rebuilt right now (it was rebuilt then failed right away so the tech is fixing it under warranty) and while i am waiting i decided to buy a large transmission cooler rated for 22,000 gross lbs and i got it for $40. I was also planning to use synthetic ATF this time but when talking the mechanic he said there is no reason to install a cooler if you use synthetic (Amsoil) since the synthetic lowers the temp anyway and it would just be a waste.
I don't really care, for $40 i think it's worth it especially in summer when my step van gets hot, the engine runs hot and i sometimes carry a lot of weight in it. But i wonder if it could actually cause the trans to run too cool in cold weather to have both a cooler and synthetic fluid - is this a valid concern? Any problems with having both?
thanks,
Paul

I have never seen synthetic fluid lower temps. I think it is great stuff and use it because it will lubricate better under extreme heat. Transmission cooler is the only significant way to lower temps in the trans. Your mechanic is wet behind the ears.
mike

I have never seen synthetic fluid lower temps. I think it is great stuff and use it because it will lubricate better under extreme heat. Transmission cooler is the only significant way to lower temps in the trans. Your mechanic is wet behind the ears.
mike

:exactly: What Mike L. said.....he's a top tranny guy. The syn fluid can tolerate higher temps without breaking down, but just because the fluid can work at those temps doesn't mean everything else in the trans will. The cooler is the way to go + it will add a bit more fluid capacity, and speakin' of that, a larger trans pan can help some too.
JP
Oh on edit: if you don't have a trans fluid temp guage, that might be a good addition also. Put it in the trans-pan that's the temp of the fluid going into the trans itself.

MikeL,
does having a large trans cooler in front of the radiator affect the engine running temp in summer? IN other words, does it block the flow of air to the radiator, affecting it's ability to cool down?
thanks,
Paul

MikeL,
does having a large trans cooler in front of the radiator affect the engine running temp in summer? IN other words, does it block the flow of air to the radiator, affecting it's ability to cool down?
thanks,
Paul

It can if the cooler is too large and radiator too small or fan too small. There are a lot of variables here. Generaly you will want the cooler spaced away from the rad. at leat 2 inches and the optimum place is either upper or lower portion of the stack so that you get the optimumair pull from the fan blades. Remember that the center of the fan pulls no air, but sometimes you don't have a choice.

Totally agree with Mike. I switched to synthetic AmsOil for the tranny and I had gauges and saw no drop in temps with the switch. Major, major improvement with an added tranny cooler. The Hayden I had installed keeps the temps so low..........well I took a trip the other day and it was in the 60's and the temps barely got above 100. I have gauges on both lines so I know what's coming and going. I feel like this will do the trick as I was hitting 160+ on average without the cooler, especially when towing my fiver.

Mike, I respectfely disagree and agree. Synthetic fluid does lower fluid tempeture but not much, 4 to 5 degrees. Results from tests running up and down a mountain all day with different coolers and fluids.
Grease, synthetic fluid and external cooler is the way to go. I have that combo on all my vehicles.