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Here's the question! I have a turbo 400 in a big block chevy v-drive day cruiser. It is set up with a tranny cooler that only runs water through the cooler when the boat is moving through the water. When the boat is setting still at idol running the engine will the tranny build up enough heat to ruin the tranny? I have had the tranny rebuilt a couple of times and am wondering if heat build up from the transmission not having cool water running through the cooler at idol and cooling the fluid is causing the thing to go south. There is no torque converter being used which I beleive is where most of the heat from a transmission comes from under a load.

If some of you could shead some light on this subject I would grateful.
 

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Here's the question! I have a turbo 400 in a big block chevy v-drive day cruiser. It is set up with a tranny cooler that only runs water through the cooler when the boat is moving through the water. When the boat is setting still at idol running the engine will the tranny build up enough heat to ruin the tranny? I have had the tranny rebuilt a couple of times and am wondering if heat build up from the transmission not having cool water running through the cooler at idol and cooling the fluid is causing the thing to go south. There is no torque converter being used which I beleive is where most of the heat from a transmission comes from under a load.

If some of you could shead some light on this subject I would grateful.
I'd be looking for a new tranny builder if it was me...had a "monster transmissions" tranny in a car that had twice the power they rated the transmission for and it held up very well and i think it was only about $1000 shipped. try giving them a call and asking how much to build your trans for you should be even cheaper. my buddy turned me on to them because his rock crawler has one in it and lasted through 3 motors already.

Rebuilt Transmissions | Torque Converters | Transmission Parts & Much More
 

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Here's the question! I have a turbo 400 in a big block chevy v-drive day cruiser. It is set up with a tranny cooler that only runs water through the cooler when the boat is moving through the water. When the boat is setting still at idol running the engine will the tranny build up enough heat to ruin the tranny? I have had the tranny rebuilt a couple of times and am wondering if heat build up from the transmission not having cool water running through the cooler at idol and cooling the fluid is causing the thing to go south. There is no torque converter being used which I beleive is where most of the heat from a transmission comes from under a load.

If some of you could shead some light on this subject I would grateful.
I ran the same set up and the trans would build a lot of heat when idleing slowly through the channel at Havasu. The trans pump makes more heat than you would expect. I finally plumbed the water for the engine through the trans cooler and that did the trick. Cool as can be.
 

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I ran the same set up and the trans would build a lot of heat when idleing slowly through the channel at Havasu. The trans pump makes more heat than you would expect. I finally plumbed the water for the engine through the trans cooler and that did the trick. Cool as can be.
Not trying to be a dick, but what do you consider a lot of heat (trans. sump temperature)?
 

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Discussion Starter #7
I don,t have any idea about the degree of heat. All I know is that this is the second time I have had the tranny rebuilt the second rebuilder indicated that heat my have been the culprit. I am considering plumbing the engine coolant water to the tranny cooler just to be safe so I has water going through it all the time.

I would like to thank everyone that has replied to my question! I appreciate it very much.
 

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Not trying to be a dick, but what do you consider a lot of heat (trans. sump temperature)?
I didn't have a temp gauge on mine, but it would get too hot to touch and after I re plumbed the water to the oil cooler (from the engine, with pressure from the water pump) I could touch the trans and not get burned. I thought that was a good improvement!
 

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I didn't have a temp gauge on mine, but it would get too hot to touch and after I re plumbed the water to the oil cooler (from the engine, with pressure from the water pump) I could touch the trans and not get burned. I thought that was a good improvement!
OK, thanks.
 

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Just as a reference, touch pain threshold to heat is 130-140 degrees F in most humans. Oil at that temp is on the cool side as it relates to running temp in engine or transmission. So my point is, if you can't lay your hand on the transmission case, it has no bearing on the oil being too hot.

Excessive heat will cause atf failure, turning it brown and smelling. This occurs up in the mid to high 200ºF range (way above the temp water boils at). This is a level far above human heat touch tolerance. Having built quite a few 400's in a former life I can say with some degree of knowledge that not a lot of heat is generated at idle as it relates to oil running temperature range. There is simply not a lot of friction creating heat going on at that level. Yes the pump is creating pressure heat and the planetaries are creating some friction but there is just not a lot of load. Yes it will be hot to touch, but again 140ºF isn't hot for atf. All just for reference on what is hot and what is not.

Consider that in an average vehicle, the "cooler" is in the radiator. The coolant medium in that radiator is operating in excess of 200ºF (the water). While it may be cooler than that at the radiator return side to the engine after being cooled by the fan and airflow my point is that the atf is still being "cooled" by very "hot" water. Transmissions typically go from 100K to 200K miles in these conditions, properly serviced. I would venture to say if a marine trans is failing at idle conditions, without coolant water flowing, there is a transmission problem and not a heat problem causing it.

I have seen many and owned one ski race boat with force fed trans cooler that sees little water flow at idle. Never seen a trans heat problem due to it.
 

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First thing I would do is install a trans temp gauge on your dash so you can monitor the situation. I believe you'll find, as others have suggested, that idling is not the source of the problem. More likely, your cooler(system) is not be doing the job while you are at speed (a clogged line/cooler, or improper plumbing).
 
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