Hi all!

As I'm working on my engine, I wondered what the differences in principle are between the full flow oil cooling (as fitted to my UK spec V12 from 89) to the relief flow version (Iirc commonly fitted to the US models!?)?

As far as I can see on the Jaguar Classic Parts site, the relief flow system comes from the oil filter housing and then returns from the oil cooler to under the engine (to the sump) where as the full flow returns back to the oil filter housing.



Are there any other differences? Like funtion or maybe effectivity? Or is the relief flow a better cooling method or is that the full flow?

 

Daim
The world is divided upon this subject! Basically, all XJSs, indeed all V12s, had relief flow until about 1988 when they were changed to full flow. I believe that German market cars had full flow fitted earlier than other markets, owing to the sustained high speeds they Germans are famous and envied for.
The relief (or bypass) flow system is as you describe: The V12 oil pump produces about 3 times the volume of oil that the engine working internals need. On the relief flow system, 100% of the oil from the oil pump get pumped to the filter, after the filter the oil goes to the engine internals; but the 2/3rds excess gets diverted via a pressure valve to the oil cooler. From the cooler it is returned directly to the oil pump inlet (which also takes oil from the sump pickup).
The full flow system takes all the oil to the cooler from the filter, then all of it back to the filter housing, at this point the 1/3 the engine needs goes round the internals and any excess is bled via a valve into the sump. In the event of the cooler line getting blocked, there is a valve in the filter housing that ensures oil can go directly to the engine internals.
There seems to be no actual data available about the relative oil temps each type produces under hot running conditions. My car is a bypass flow engine and I have a project for this summer, always assuming w get any hot weather, to carefully measure oil temps in the cooler, the sump and the cam covers. These I shall note and post.
I have all the bits needed to convert my engine to full flow. In the event of the temps I measure being too high for comfort, I shall convert to full flow and do the same measurements again, and post those too.
Having said all that, my car has done about 125,000 miles and the thing seems in great shape, pulls like a rocket, and is showing no wear at all on the cam lobes. So I shall probably prove there is no real difference! But heck, I am retired so why not!
Greg

 

Cheers Greg! That would be interesting to know. I like facts that are measurable... I guess that there must be a reason why Jaguar swapped to full flow coolers... Maybe their tests showed it ran cooler? Who knows (at the moment at least )...

 

Look forward to reading the results.

 

ditto!

 

Cool all the oil in one pass, or part only a time. Side issue, effect on OP.


Early non Jaguar critters use partial flow filters. It works. Assures plenty of flow to the bearings while filtering some. Eventually all gets filtered. And cooled, sorta.


Early hot Rodders converted part flow Ford V8 Flat heads from part to full. Just drill the block in a strategic place. I opted out not needed.
Worked just fine. Henry and his engineers were/are pretty smart guys.


Carl

 

Regarding relief flow oil filtration, a neat idea is to combine our normal full flow oil filter with an additional relief flow oil filter that filters down to microscopic particle sizes.