Gearbox Oil Cooler for BW35

[Peter Mueller]

Dear All

The replies to my recent inquiry about spark plugs have digressed a little but have yielded some information that I thought might be interesting for others as well. So this info can be found more easily I'd like to post it here separately.

As I am in the process of having the gearbox rebuilt, the question of adding an oil cooler for the 'box has emerged. I have heard voices against and for it. However, those supporting the idea seem to be in the overwhelming majority, citing better maintained viscosity, no risk of coolant leaking into the gearbox, and general benefits for the longevity of the gearbox as the most prominent advantages.

I have had a look around and found the following:

• Sets (including all fittings and pipes) for the Borg Warner BW35 and 65 can be had from Kenlow (Product #: AT13LTA) or from ThinkAuto (Product #: AT/7) ==> careful, on their website it says AT/8 but that is wrong! )
  
• The cost (correct for September 2006) inclusive of all fittings, pipes, VAT and delivery is: Kenlow £90.72, ThinkAuto £133.16. One might say that one gets what one pays for but a.) Kenlow is a well-known manufacturer and b.) the price difference is even more peculiar, as ThinkAuto claims that Kenlow buys the components for their oil coolers from them. How that can create a price drop of almost 50% between parts manufacturer and end-supplier is anyones guess, and looking at the specifications they should be more or less identical twins.
  
• Neither the Kenlow nor the ThinkAuto kit come with thermostats (helps to warm up the oil more quickly and then maintain a more even temperature range). But ThinkAuto supplies individual thermostats for this application that are push-on versions for easy in-line installation. The product # here is OT/1B and it costs £22.45 + £6.95 delivery and 17.5% VAT. I have checked with Kenlow and they say there is no reason why it should not fit and/or work.
  

My choice will be the kit from Kenlow combined with the thermostat from ThinkAuto.

However, there are alternatives, of course, which could result in some savings on cost. I know that Dave Cole (for contact see under Regional Meetings), for example, found a Mocal cooler (also sold by ThinkAuto) on E-Bay and then bought the individual fittings etc. separately. According to him it works a treat. So you don't have to feel tied to a ready-made kit should you be interested in installing a cooler.

Peter

[Smallfry]

You do not need a thermostat on an auto transmission. There are no combustion products to disperse which is why its needed on an engine oil cooler.

The requirement for a clutch band type auto is to keep the oil from getting too hot. You will only have a problem with the oil being too cool if you either live in an arctic environment, or you have installed the incorrect grade or type.
The oil will only get too hot when either the gearbox is working too hard.........towing a caravan up the Stelvio pass for instance........or sitting in traffic, and its sitting in traffic that is by far the biggest problem you are going to have in this country.

When the car is sitting in traffic there is no airflow through an oil to air cooler (an oil radiator) so it will be of absolutely NO USE ATALL ............but the cooler in your water rad will be helping provided you have a decent (16 inch) electric fan fitted, and it will also be improving matters when you are towing too.

Engines incidentally work the other way round, they cook their oil much more when they are thrashing down a motorway when airflow is obviously good.

As the chances of water contamination are not very high in the grand scheme of things. and a small amount of water contamination will be noticed when you check the oil ( I take it you do check it) and is only really harmful if it is left standing for a long time.

If you are worried about the oil, go synthetic. For the rest, keep the cooler in the rad and spend your money there, and on a big electric fan.

[Phil Nottingham]

There you are then - even Smallfry agrees with me! While I accept there is a risk of overheating and contaminated ATF this is very low after all a lot of these cars have survived without an air cooled caller. The DG box had none and Rover did put a separate one in front of the rad with the Mk3 when the BW35 was used.

Its inbred in me to assess risk and return on money invested and unless I intended doing many thousands of mile per annum or towing a heavy trailer regularly its clear to me this would be a very poor investment and you would be better spending it on a Kenlowe rad fan even.

There is clearly something wrong with you box and you had tried everything possible without removal

[Smallfry]

Well there you go then Phil, it had to happen sometime !

I guess I assess things from a different angle than you. I do not worry too much about the cost versus benefit when making changes, although of course value for money is an important factor. What concerns me more, is that any modifications, changes, or accessories should actually do the job for which they are intended, AND actually be of benefit, AND an actual improvement, rather than just a perceived one.

In this case, even taking into account the "risks", I feel that this would be a retrograde step.

[harvey]

If you dont think a seperate gearbox coller is doing anything when stationary, see how close you can put your hand to it. Then remember that all that heat would be going into the coolant.Without this extra heat you probably wouldn't need such a big Kenlowe.
As for the coolers in the rads they dont give the number of problems they used to because the milages covered are less. Have a problem with it that you don't notice before the winter lay up and see what a gearbox performs like after being sat for 6 months with water in it.I worked on the cars when they were used as everyday transport and we did plenty.At the end of the day you make your own choice

[Phil Nottingham]

I've used mine every day for including towing but I suppose there is always a first time!

[harvey]

That's right, and if it does happen and it's not noticed the cost can be high.You can only speak from your own experience, and that would appear for it to not be a problem, and long may that continue.I can only speak from mine, which is mostly P6 related but in this case all the same things apply, and having worked on those day in and day out for over 20 years, and reconditioning gearboxes as req'd, I found coolers in rads to give problems.
After finishing with repairs I have done recovery work for six or so gearbox specialists, and they've all had problems on various vehicles to a greater or lesser extent as well so it's not isolated instances.

[Phil Nottingham]

By definition though you only see the ones that actually have gone wrong? Hardly representative? However I agree if it does fail the damage caused would be fatal to the box.

[harvey]

That I can't argue with! I do only see the ones that have gone wrong and there have been many.If I was still doing repairs , I would not champion my current point of view quite so vigourously (is that spelt correctly?) As it is I only have a point of view. I NEVER saw coolant in the transmission of a car with a seperate cooler. (unless you count a mini auto with a blown head gasket!)

[DaveCole]

I’m sorry Smallfry I disagree. A separate BW35 cooler must surely make a difference. The built in cooler tube passes one hot fluid through a chamber containing another hot fluid, I’m not a scientist but that surely can’t be very efficient. A separate cooler dissipates the heat to atmosphere, which even in stationary traffic is cooler than inside the water radiator. Also remember that one heat source passing through another heat source ‘recycles’ the heat already generated, where as a separate cooler removes the heat from the source and vents to air.

I have a 9-row oil cooler fitted to the radiator using the same pull through ties as the Kenlowe fans etc. It has a small but efficient surface area so does not affect the performance of the main radiator and has made noticeable improvements. Firstly it will prolong the life of the slush box and fluid. Secondly, you get a much crisper and smoother gear change. Thirdly, when in traffic queues and the water temperature increases, the fluid is heated by the water and loses its viscosity, which means when you can accelerate the car won’t because the box can’t change gear and possible damage occurs.

I would recommend fitting a separate cooler as part of a ‘reliability improvement program’ (sounds posh but I made it up!!) electric fan, electronic ignition etc.
As far as cost is concerned, if you feel competent enough to do it yourself it can be done for about £30 (I bought mine off E-bay)

David

[Smallfry]

I maintain that standing in traffic, when its most needed, an oil radiator will have negligable heat loss, whereas an oil to water cooler will be giving a steady reduction, and when a correctly set electric fan kicks in it will still be doing this, while your oil rad will still be doing next to nothing.

At the end of the day, one must make ones own choice, but I would not recommend this for a BW35, and I would certainly not fit one myself.

[harvey]

I'd be interested to know what Borg Warner thought, they supplied 35 & 65 boxes to both Rover and Triumph at the same time and the Rovers had the coolers in the rads, and the triumphs had seperate coolers.

[Deleted]

How come the autobox needs its cooler the most "when in standing traffic"?
It would be doing no work and therfore not generating any heat wouldn't it? Can't see the point of the argument here - or am I just thick?

Please explain in more detail 'cos I have and oil to air cooler fitted!!!!

Adrian

[harvey]

You're pretty much right Adrian, providing you shift into neutral, but it will generate a bit more heat when sitting in drive. But while stationary the cooler can still dissipate the heat built up when driving. Not all boxes have coolers, the BW65 when fitted to a triumph dolomite doesnt, but when the same box is fitted to a stag it does, the only difference being the stag engine is nearly twice the size, so when given some stick the stag has more grunt and so gives the box a harder time generating more heat.
This is another subject that has no right or wrong, it's just a question of making your own mind up, Knowing the advantages and disadvantages of each way, and going with what you feel most comfortable with.