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I suspect the first thing to do is verify the temperature being reported.
Then, if found to be out of spec, pursue the "warranty" involved in what
your invoice says was replaced.
Thanks for everyone's input, I really appreciate the help and suggestions. @aquifer has had the same problem and it, too, turned out to be an overheating transmssion. The only difference here is that my radiator and fans are new, genuine parts.
'll be seeing a different transmission "expert" next week, but thought I'd summarise where I'm at for any of you that need something to help you sleep
Background in short:
I've owned the car for over 10 years and have never had this issue.
Transmission Overhaul (11 July 2023)
Radiator/Cooling Fans Replaced with new, genuine parts (16th September 2024)
The first instance of the transmission refusing to upshift was early November in city traffic. All subsequent incidents have been in city traffic, however, anecdotally, there doesn't seem to be a problem on the freeway/highway.
After the first two incidents, I've modified my OBDII reader to display transmission oil temp. When the refusing to upshift occurs the transmission oil temp is over 110*C / 230*F (and has reached 124*C/255*C).
Transmission oil temperature steadily increases (see graph below)
Coolant temperature sits at 95*C/203*F or below (the cooling fans kick-in at 95*C/203*F)
There are no fault codes from the ECU (OBDII) or messages on the dash.
I believe the transmission is overheating, however, I'm unsure as to why, possibly:
The first instance of the transmission refusing to upshift was early November in city traffic. All subsequent incidents have been in city traffic, however, anecdotally, there doesn't seem to be a problem on the freeway/highway.
That bit at least makes perfect sense to me. I used to have a SAAB with very hard shifts between 1st & 2nd when the box got too hot. That'd play up on a 20min drive into town if I was stuck in traffic, but I could drive it for 5hrs to a ferry in Scotland & it was fine when moving all the time so the cooling circuit worked better.
I that car's case it was a known fault with the box where the solenoids wore & caused it, a bit like the weakness of the box in normally aspirated x308s.
The transmission specialists believe there is nothing wrong with the transmission itself - based on what they can check without removing the transmission. They don't believe that the torque converter is faulty as the gear changing, including the reluctant upshift when the transmission oil temp is over 115*C / 240*F, is "behaving" normally with none of the characteristic symptoms you'd expect to see.
...which brings us back to the question, why is the oil overheating when the engine coolant isn't (with a new, genuine radiator in place).
My mechanic, not the transmission specialists, has trouble believing that it could be the radiator as it cools the transmission oil by exchanging heat with the engine coolant.
...so, next step, either replace the radiator or add an external transmission oil cooler.
Replacing the radiator: Jaguar has agreed to refund me for the radiator, they can't exchange it because they are out of stock of radiators :-( So I'd need to get a non-genuine radiator.
External transmission oil cooler: It's just a matter of knowing what sort and if it will fit. This would probably be the best option if, for no other reason than ruling out/confirming the radiator as the source of the problem. And, at a much lower cost.
The only way I’d go with this is to remove both transmission oil cooler lines at the radiator and using an air gun with a blunt rubber tipped nozzle to blow through the cooler in both ports to do a comparison of air flow. If you still aren’t sure, I’d either get an external digital temperature probe down inside the dipstick tube until it’s in the oil pan or get a large bar and plate style TOC and route the lines for externally mounted trans cooler.
The only way I’d go with this is to remove both transmission oil cooler lines at the radiator and using an air gun with a blunt rubber tipped nozzle to blow through the cooler in both ports to do a comparison of air flow. If you still aren’t sure, I’d either get an external digital temperature probe down inside the dipstick tube until it’s in the oil pan or get a large bar and plate style TOC and route the lines for externally mounted trans cooler.
Thanks for the advice. Do you think it's likely that a manufacturing fault has caused a restriction in transmission oil flow through here? I don't know what goes on inside these radiators to understand how a new radiator could be faulty, in particular, the transmission oil cooler pipes - they appear so simple.
Just a quick update. At this point I haven't added an external transmission cooler, I'm this point I'm still resisting this approach.
@aquifer I note that one important difference between my issue and yours is that mine will occur within 40-50 mins or so of driving, so it's much quicker than yours (you mentioned a couple of hours).
My next step is to:
Measure the temperature of the transmission housing (to verify the temperature reported by the sensor).
Measure the flow/return temperatures.
Check the flow through the transmission cooler lines and through the radiator.
Given the transmission oil passes through the radiator and a heat exchange occurs, I can expect the transmission oil to be cooler than the engine coolant - so that means normal operating temperature for the transmission must be approximately 85*C / 185*F to 95*C / 203*F - with bursts up to 102*C / 215*F
Given the transmission oil passes through the radiator and a heat exchange occurs, I can expect the transmission oil to be cooler than the engine coolant - so that means normal operating temperature for the transmission must be approximately 85*C / 185*F to 95*C / 203*F - with bursts up to 102*C / 215*F
Not necessarily. While a heat exchange certainly takes place in the radiator,
the efficiency of the exchange has many dependencies which could reduce
the effective temperature of the "cooler" effluent. There could be restrictions
or built-up solids that could impede flow-through, or other restrictions which
could lead to less than desirable cooling of the fluid.
The only way I’d go with this is to remove both transmission oil cooler lines at the radiator and using an air gun with a blunt rubber tipped nozzle to blow through the cooler in both ports to do a comparison of air flow. If you still aren’t sure, I’d either get an external digital temperature probe down inside the dipstick tube until it’s in the oil pan or get a large bar and plate style TOC and route the lines for externally mounted trans cooler.
This is good advice. It is possible that the internal lining of the hydraulic lines are partially collapsed, or that they gradually collapse as fluid heats up and builds up behind the inner liner. I replaced both of my coolant lines to account for this possibility because I was out of options at the time. But in my case it didn't help. That's when I went with the external cooler and haven't had an ounce of trouble since. I concluded (right or wrong) that there was a restriction in the radiator someplace that slowed down the oil flow just enough that the heat would slowly build up until eventually it got too hot. Like yours, my engine coolant temp was fine the whole time.
I recommend checking the cooler lines. The line on top is a bugger to replace if you end up needing to, but I got it done so it's possible. When I went through this, new OEM transmission cooler lines were available. I don't know if they still are, but checking yours is a good idea.
Edited to add: when you have the lines off to blow through them, you could figure out the direction of flow (I don't recall which line is in and which is out), and then blow compressed air backwards through the factory cooler. Prepare for a mess, but if a chunk or two of crap from the transmission got stuck up against any of the passages inside the cooler, it might blow them back out the port. Just thought of that right now. I don't know why I didn't think of it when I did mine! Can't hurt to try it. Or pump fluid backwards through the cooler maybe? Just thinking out loud here.
Troy, sorry for the delay. To answer your question (sorta) from 1/13, there’s no telling how the manufacturing process and quality control was to make sure everything is as it should be when it left the facility. Who knows if there’s a plastic plug or other material debris (slag?) that could be lodged in there sideways impeding flow. Sadly the only way to confirm is to have some sort of fluid machine to measure flow in both directions. With that being said, I’d bypass it entirely and just get a good quality bar and plate (B&M) TOC to compare with the in radiator TOC.
Troy, sorry for the delay. To answer your question (sorta) from 1/13, there’s no telling how the manufacturing process and quality control was to make sure everything is as it should be when it left the facility. Who knows if there’s a plastic plug or other material debris (slag?) that could be lodged in there sideways impeding flow. Sadly the only way to confirm is to have some sort of fluid machine to measure flow in both directions. With that being said, I’d bypass it entirely and just get a good quality bar and plate (B&M) TOC to compare with the in radiator TOC.
I agree. That will very likely eliminate the problem entirely and the true cause can remain a minor mystery. I had a machinist make two fittings for me. On the female side they were perfectly beveled and threaded to accept the transmission cooler lines with no modification. On the other side was 3/8" hose barbs. Then I ran hoses to the external cooler. I admit that I had an advantage, because I had replaced the transmission cooler lines. Which meant that I had the old lines laying there. I cut the end off one of them and gave it to the machinist so he could create the exact fitting I needed to accept the cooler line. I don't think I would just cut the cooler lines and try to clamp on a rubber hose, because it will leak. Plus, if you ever want to go back to the factory cooler, you'll want to have your threaded fittings intact.
Thanks everyone, I think I'll add "Force compressed air through the transmission flow/return sockets of the radiator".
Pessimistically, assuming none of the above will shine any light on the situation, I'll progress with the external cooler. I'm hoping off the shelf adaptors like these will work (to avoid cutting lines):
If I remember correctly. Cooler lines at the radiator end are quick connect type? It's been many years since I've done oil flush to my car or any ford era jaguar. If they are quick connect. Welding is almost the only way.
That cooler hold capacity is 100ml I don't think it's good idea
Look at Hayden coolers minimum 250-500ml trucks use 1 liter capacity but I'm not sure if there's place to fit large oil cooler in the x308 Hayden very good and way cheaper than that one in the link if you want want something better then greddy or mishimoto
That cooler hold capacity is 100ml I don't think it's good idea
Look at Hayden coolers minimum 250-500ml trucks use 1 liter capacity but I'm not sure if there's place to fit large oil cooler in the x308 Hayden very good and way cheaper than that one in the link if you want want something better then greddy or mishimoto
There isn't a lot of space, I'm looking at 1 inch width.
I may be wrong, but I suspect the fluid capacity isn't as important as the heat transfer rate (BTU/HR)? I believe that the x308 XJR transmission oil cooler capacity is ~300ml (~10 fl.oz) so, while this is only 100ml, it has a heat transfer rate of 15,710 BTU/HR which is the best rating I've seen for a radiator of this width. Annoyingly, it seems many manufacturers rate their products based on vehicle type rather than heat transfer rate, eg.
There isn't a lot of space, I'm looking at 1 inch width.
I may be wrong, but I suspect the fluid capacity isn't as important as the heat transfer rate (BTU/HR)? I believe that the x308 XJR transmission oil cooler capacity is ~300ml (~10 fl.oz) so, while this is only 100ml, it has a heat transfer rate of 15,710 BTU/HR which is the best rating I've seen for a radiator of this width. Annoyingly, it seems many manufacturers rate their products based on vehicle type rather than heat transfer rate, eg.
I wouldn't go lower than 300ml since it came from the factory however if there's no space at all then you have no choice except the one with 100ml capacity then adding spal fan then probably will improve the cooling . Before doing that ask the shop what ATF they put in the transmission it could be wrong atf
