Just Discovered Where the V8 Auto Oil Cooler Is!!

keynsham1

keynsham1

Active Member
I have just removed the radiator from my V8 Auto NADA as it is leaking and needs a fix. I have always been interested to know what part of the radiator is the oil cooler for the gearbox and now I know! This might be common knowledge of course but the oil cooler is actually a double skinned tube about an inch in diameter which lives in the offside tank of the radiator, the offside being the cooler side. Oil flows up through it and back through pipes which exit at the bottom of the tank one above the other. I had always assumed that the oil cooler was a part of the finned radiator, like oil coolers usually are, but apparently not!

You learn something new every day!
 
A very common cause of cross contamination between coolant and the ATF, which can become a big and expensive problem.
If you have the radiator out, I'd take the opportunity to get yourself a separate cooler.
 
I went down that road. ie reroute the oil cooler from the base of the radiator to an exterior radiator type that sits in front of the main radiator. An easy adaptation and a more efficient cooling for the g/box. Cant recall the name of the kit, but a quick measurement to make sure it fits between the radiator and the front body and you are away. The kit came with the oil pipes and mounting clips.
 
I have been told the reason failure of an auto cooler can be fatal for the tranny is that the lining on the clutch plates inside the tranny is glued to the plates with a water soluble glue....
 
Trans coolers integral to the rad are common on Yank vehicles, I’ve seen a couple of failures.
 
I recall reading about a transmission cooler failing in the radiator a while back. Did a quick search and found this one.
T

Post in thread 'Water in gearbox'

Ok, gone for a middle ground approach - the radiator was fine prior to starting to leak into the trans cooler section even on warm days and in traffic so I have flushed that area out and plugged off the trans cooler lines to retain the current radiator even with its internal leak. I don't think it leaking into the trans section will impact the flow to any great degree since it was reasonably small rather than gushing out, and the plugs i have used are screw on so can easily be removed if need be.

I've also purchased a decent sized trans cooler and have fitted it in front of the radiator...

Funny that is not the post I was thinking of. Same story, coolant leaked into the transmission. The owner was hopeful no damage had occured but that was not to be.

It is definitely not a wise move to keep using it when there are plenty of alternative coolers available. Running a dedicated cooler with the inbuilt unit disconnected is the best option, then when the radiator needs a recore, have the inbuilt unit removed altogether.
It is a poor feedback design in any case.

Ron.
 
The reason they put the cooler in the radiator tank is because both tansmission and engine run at about the same temperature. There is no need for a thermostat in the oil line in cold climates.

Ron, they may have been my post from a few years ago when I lost all my transmission fluid to the radiator....All fixed now. I didn't go the seperate route as I'm preparing to go four speeder which will require a bigger, seperate unit anyway.
 
mikecoombs said:
The reason they put the cooler in the radiator tank is because both tansmission and engine run at about the same temperature.
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Hi Mike,

I am aware of the theory behind the feedback loop, unfortunately in the case of Australia is just works to shorten the life of the transmission. I recall when I was having the transmission rebuilt in the 1990s (not a great decade for my transmission, it failed a few times), the transmission mechanic said that my transmission had been running too hot. The seals had gone hard resulting in scoring plus there was (I'll call it staining of components from overheated oil). He said your factory oil cooler in the radiator is not worth a pinch of salt and to run another cooler. After that I fitted another cooler running in series with the inbuilt unit. That helped in extending service life but nothing like the longevity that I would ultimately obtain when running a dedicated transmission oil cooler.

Ron
 
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I'll definitely use an external unit when I have the ZF box fitted. i've cooked the BW35 a few times but always from using the car to tow something too heavy up hill...The actual box was rebuilt by Borg Warner with the Taxi pack BW 65 components designed for the P76 and Ford taxis. The very first BW 35 had a second cooler (and rear pump) that used the torque converter fan for cooling but it was dropped very early on
 
mikecoombs said:
I'll definitely use an external unit when I have the ZF box fitted. i've cooked the BW35 a few times but always from using the car to tow something too heavy up hill...The actual box was rebuilt by Borg Warner with the Taxi pack BW 65 components designed for the P76 and Ford taxis. The very first BW 35 had a second cooler (and rear pump) that used the torque converter fan for cooling but it was dropped very early on
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I have heard of the taxi pack but my understanding from what the transmission mechanics said to me over the years was it was all Ford parts. No one ever mentioned the BW65. The fully upgraded BW35 was designated M51, which is what my transmission is.

Ron
 
I'd scored one of the brake drums after the band went down to metal. That writes off the whole gearset, so BW rang to ask if they could use a 65 set as they didn't have any 35 ones in stock... only difference was the hardness and tooth material was better in the 65 box. I think later they just sold the one set for all boxes. The job was done out at BWs plant in Sydney way back in the 80's. The biggest difference between the two is the placement of the piston for the reverse band; on the 35 its a seperate unit bolted upwards onto the inside of the case. on the 65 its built into the side of the case. The former had a habit of snapping off, preventing reverse from working and adjustment required removing the sump.
 
The transmission fluid going into the radiator acts as a heat exchanger which brings the coolant up to temperature quickly to aid engine efficiency rather than keep the transmission fluid cool.
Fit a separate cooler, if your transmission could thank you it would.
I have just stripped down a very low milage BW35 from a 2 Litre engine derived vehicle.
This had no facility for fluid pipes to be fitted to either radiator or oil cooler, it looked as though someone had taken a blowtorch to everything inside which gave it a heat treatment look.
 
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SydneyRoverP6B said:
Out of curiosity, how many miles does your transmission normally cover between rebuilds?

Ron.
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It was 52000 miles and 52 years old when it had the first and only rebuild. There was nothing major wrong with it but it was during Covid and I had nothing better to do than take it out!! It was done professionally and I have to say is smoother with gear changes now. I have only done 1000 miles since and all is still well!!!
 
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