Simple question, but not obvious to find an answer on the web.

Does the 6sp 6hp26 have a built in thermostat for its oil. i.e. does it re-circulate oil whilst warming up, then open a thermostat to run oil out to the cooler to keep it cool

or does it always flow oil forward to the cooler regardless of oil temp? (i.e. no stat )

any one know? V8 or else ...

As far as I know it works like the 5-speed system. All the transmission’s lubrication flow goes through the cooler all of the time and it’s the water side of the oil cooler which is controlled by a thermostat, depending upon the temperature of the coolant.

This is from the workshop manual :

The liquid cooled Transmission Oil Cooler (TOC) is mounted to the fan cowl. It is fed coolant from the sub-cooled section of the radiator, which is controlled by the Oil Cooler Mixer Valve (OCMV).

The liquid cooled Engine Oil Cooler (EOC) is fed coolant from the sub-cooled section of the radiator, which is controlled by the OCMV. It is also mounted to the fan cowl below the TOC. Both the TOC and the EOC are connected in parallel.

The OCMV is a 2-stage valve which controls the heating and cooling of the engine and transmission oils. The operation of the first stage is to warm up both oils from cold to improve emissions and driveability. The second stage is fully operational once the coolant temperature reaches 91° C (196°F) and allows cooling of both oils (starts to open at 84°C (183°F)).

Click image to enlarge

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Interesting, thanks Phil.

The reason I ask is that whilst I understand that there is the suggestion that the quicker-heated coolant can be used to heat the engine oil from a cold started engine, this doesn't actually happen. Beside the engine oil filter, there is a thermostat in the housing that won't open up the engine oil cooler lines until the engine oil itself reaches a certain temp. So no heating comes from the coolant in the early stages. ( This is from lying under the car feeling the various pipes as the engine goes through a cold start )

So it made me wonder if the transmission oil was the same, in that a stat prevented flow to the cooler until upto temp - but it doesn't seem to.

This is me coming back to the idea of an additional oil cooler for the transmission - a possible mod I had thought about for my previous L322. The fitment of such would depend on knowing the flow of the oil. V8 or else ...

If I remember correctly the SCs have an additional engine oil cooler (driver side RHD cars) in front of the front wheel. That may be the reason the engine warm up is different.

I also understood that the two oil/water cooler/heater units are used to aid warm up of the transmission and engine to reduce emissions (and wear).

By the by, NEVER EVER put pure water in the cooling system as these units can corrode very quickly (early years only) as happened to my 4.2 (didn't know the bloody mechanics put water iso proper coolant in). Both failed a month from each other after about 6 months. I didn't notice anything like a thermostat in/near the units. MY 2010 5.0 SC Galway green and sand interior!!
Have the Faultmate MSV2 Extreme to be tinkering with the settings etc. !!

Yes, mine has the radiator cooler on the rhs, which is why I temporarily disconnected the heater/cooler on the lhsas I knew I would still get engine cooling for the oil.

As I say I'm toying with adding a transmission cooler for towing and just trying to understand the flows of oil and their temp changes V8 or else ...

Another cooler on that system would need to be on the return to transmission side of the flow, otherwise you create a push pull sort of situation. ie you are cooling the fluid only to have it re heated and I think the engine side of the equation is going to win that fight.
A bigger cooler on the return side maybe, instead of another cooler.
Is the whole system (oil, trans, coolant) not a closed loop? its all running at the same temperature when at operational temperature?

Lowering engine temp is most likely the easiest route to take.
Have you got an ID2 tool to monitor trans fluid temp?

I have done the stat mod on my V8 and its running around 15c cooler at all times now, thats a pretty good amount of cooling capacity in reserve over the standard set up.
Going on the temps quoted by Phil that means my trans stat is open (just opened) I run around 92-93c when on the highway or normal driving, it will fall to about 89c on a long down hill (off the gas) run.

Building more capacity into the system by way of more coolant is another option.
If you go down the extra cooler on the trans side get something rated for the pressure, Phil can most likely confirm, but I think the ZF cooler is rated at 150PSI.

I think the coolant stat in the Jag engine is lower than the BMW systems. At a hunch its around 84degC from other forums. Although not definitive, i think thats about right from just the smell of the engine after being worked - it definitely doesn't smell as hot at the BMW unit used to when it ran with the higher temp state.

It does all appear to be closed loop with the 3 systems inter-mixing their temps, and all relying on the main radiator to do the actual cooling. I'm fine with that for the most part, and it seems to be a system that works.

But

Even the engine oil has an additional cooler for the supercharged ... implies to me that there is a need for cooling beyond that which the normal radiator system can provide to the engine oil. If thats the case for the engine oil, then could it be that the transmission oil could reach a point where it needs the same additional cooling? I personally think so. We are looking at getting a horse/utility living trailer that realistically will be 2.5t and as aero as a brick. Part of the idea is that we would use to as a caravan type setup and take it long distances up north. With the hills and roads, I don't want to be feeling that I'm cooking the transmission - I'd rather build in that extra cooling capacity and have peace of mind.

As for flow of an additional cooler ...

If I plumbed a cooler in series after the heat exchanger, then i'll always be cooling the return flow, and in theory I could be potentially over-cooling the fluid in some circumstances ( as it needs to be warm to work properly, just not too warm).

So I think I would need to involve a thermostat which would valve the flow to the additional cooler. Easy found off the shelf parts. This thermostat would then only flow oil to extra cooler when the oil was upto temp, and so would also close if I was over-cooling.

Would it then be better to add this in series with the existing cooling?



or to be in parallel with the existing circuit ...



I think if it were in series, then in situations where the trans oil is getting too hot, I'd be first dumping that extra heat I want rid of into the radiator system and the rest of the engine.

If it were in parallel, then I'm dumping the excess heat outwith the other parts and into the air. But if it were in parallel, is there the potential that when the stat is closed, I'm creating a short circuit for the oil to flow, and this would prevent oil getting to the normal heat exchanger ??? V8 or else ...

I think I like the idea of an air heat exchange.

The P38 has a neat air trans cooler.
I dont tow with my P38 but even on the hottest of summer days I have not seen over 78c on my trans pan.

Thermal regulation within an optimal range can really only be achieved with a thermostat arrangement.
Its looking like you are well into the design stage, it will be interesting to see how it works.

Reading up a bit more, suggestion is that parallel is the better way. This is cause the flow from the heat source is halved across the coolers. With half flow the oil spend more time in the cooler being cooled. It also mean that both coolers get the highest temp fluid going to them. Heat transfer works faster where the temp differential is graeatest, so the hotter fluid each cooler gets the better transfer. So longer time in cooler and better temp differential is the way forward I think.

It's early design stages as you say, but I plan on keeping this car for a long time, and want peace of mind with it. V8 or else ...

Use pipe work as much as possible, especially around any exhaust components, hose connections are fine at the ends.
Trans fluid burns furiously, failure of trans hoses burn out lots of unloved D2s.

Get your components where you want them and get someone like Enzed or the hose Dr in to make all the connections for you, pretty sure Enzed must be in the UK. They just show up on site in a Van they have all the fittings and swageing tools with them.
Or you can just measure up and get the hoses and connections made to order and do the fitting yourself,which it seems you will be.

Well there are short rubber sections near to the heat exchanger, and the run back to the box is metal pipe. If I tap the rubber, then I only have to run another rubber hose round the edge of the main radiator to the front area. Probably able to do it with about 12 to 18" of hose at most.

My current thinking is that I should in the short term install a couple of oil temp gauges which would tell me the current running temps of the oil going to and from the existing cooler. It could in theory be that the trans temp is always below the engine/coolant temp and I have nothing to worry about. V8 or else ...