Hi,

I think I might know the answer but just thought I'd check with the knowledgable collective here.

L322 M62, driving along 80 mile journey mixed roads, gear changes felt a bit wrong and then I pulled out onto a roundabout car accelerated, then seemed to get stuck in 3rd gear. Couldn't change it in manual either.

Stopped the car, checked icarsoft reader and no errors. Checked transmission oil temperature and it was reading 135c. (no idea if that's accurate or not) Turned the car off, restarted and drove the last few miles home taking it easy with all 5 gears back again.

So my guess is it's not getting coolant through the transmission oil cooler.

Engine coolant temperature is sat exactly where it always sits, dead centre of the dial, so I assume that's fine.

Last year I changed the main thermostat to a lower rated temp, and one thing I noticed but didn't really click was how the lower radiator drain valve was less than useless and draining very very slowly.

From a quick Google, I'm reading that the main radiator might be the culprit.

Does that sound right?

Cheers.

The transmission cooler is an oil-to-water type that receives its coolant flow from the bottom eight rows of the main radiator (controlled by a thermostat). When the bottom of the radiator (or the water side of the oil cooler) gets blocked the cooler has nothing to cool the transmission fluid with, so the fluid overheats.

We had the exact same thing happen on our previous 4.4V8 Petrol L322. I had some information somewhere about it.

The oil cooler is fed from the bottom six cores of the main radiator. Within a certain VIN Range, it was a known issue where the bottom six cores collapsed internally and restricted the flow of coolant to the Oil Cooler.

Fix is to replace the main radiator (we also changed the oil cooler) and never had a problem again.

It restricts to third gear to keep the engine revs high and thus push more coolant through the oil cooler.

I'll see if I can find the range of VIN numbers.


FOUND IT!!!

This is the data from Land Rover.

Land Rover issued a Technical Service Bulletin in September 2007 for "High Engine Speeds and/or Transmission Shift Problems" which stated :

"The customer may experience high engine speeds and/or transmission shift problems after driving for 25 minutes or longer. There may also be the possibility of the transmission overheat message being displayed on the instrument cluster. High transmission fluid temperatures may be the cause of the problem"

In other words the transmission is selecting 'cooling strategy' mode as the bulk oil temperature has exceeded 140 deg. C.

The fault is caused by a partial blockage in the lower eight tubes of the (engine) radiator which supply coolant to the transmission oil cooler - supposedly caused by "depletion of the coolant corrosion inhibitor".

The bulletin states that it's not possible to clean out the partial blockage and that the radiator must be replaced.

LTB00080 - 15 Aug 2007

VIN Numbers 100042-175505

This is one of the forum threads

http://www.fullfatrr.com/forum/topic27376-15.html

http://www.fullfatrr.com/forum/topic2438.html

I wonder why it’s not triggering a fault code Des

2005 (2006 MY) L322 4.2sc Java Black, 2010 facelift conversion
1965 Lenham Lemans GT 1310 , Gulf Racing blue, FIA spec and road legal
2018 F56 Mini JCW, Thunder Grey/Black, Mulgari St2 tuned, FMIC, short shifter and Eibach springs

Hi Everyone,

Thanks for responding and confirming what I was thinking. I'll get a new rad, and then monitor temps, then change the oil cooler too if it still reads high.

Phil, yes agreed I'll also do a transmission oil change etc too. sucks thought as I only did it a couple of years ago, so it's only done about 10k miles since, but agree if it's been as high as my cheap reader says then it's ruined.

Really appreciate everyones feedback

So I changed the main radiator this morning, got the engine up to full temperature to make sure it was bled ok, and then took it out for a 20 minute drive.

The transmission coolant temperature was reading up to about 106c once up to full temperature, and stayed around there, does that sound about right?

I did take the temperature when the car had been sat overnight the other day and it read 20c even though ambient temperature was 4c, so I'm guessing there's a bit of finger in the air with the temperature sensors or the reader I'm using?

By the way I've not changed the transmission oil yet, still waiting for that to come in the post.

Cheers

That all sounds right. The transmission fluid temperature should be around the same as the engine coolant temperature (maybe a few degrees lower). The engine thermostat is nominally set to open at 105ºC. Edit - incorrect information: but the coolant temperature can exceed this at part loads as the electric thermostat heater is employed, to improve fuel economy & emissions.



I frequently measured engine coolant temperatures of 117ºC and the graph below shows the engine coolant and transmission fluid temperatures I measured on my commute to work after an overnight stop. I concur that there was definitely an offset in the transmission fluid temperature at the start of the journey relative to the ambient temperature.



Phil

Last edited by RRPhil on 9th Mar 2025 12:21am. Edited 1 time in total

Thanks Phil, that makes sense except that I replaced the electronic thermostat last year after it failed with a 88c thermostat, however even with this lower thermostat the engine temp still reads 101c, and transmission 106.

I believe that the measured coolant temperature (i.e. temperature at the sensor) is higher than the thermostat opening temperature because the coolant has circulated through the engine by the time it reaches the sensor, but whether that would explain the 13ºC difference I’m not sure.

As for the transmission fluid temperature being higher than that of the engine coolant, that doesn’t sound right. There’s a thermostatic valve for the oil cooler, whose job is to prevent engine coolant passing through the oil cooler until the transmission fluid temperature is up to 80ºC. I guess if that was stuck ‘closed’ then the engine coolant wouldn’t be able to do its job or maybe, as previously mentioned, the water side of the oil cooler is partially blocked.

It sounds like the replacement radiator has partially sorted the problem (transmission fluid down from 135ºC to 106ºC and no longer activating cooling strategy mode), but maybe there’s still an issue with the oil cooler?

Phil

Actually, thinking about it, the difference between the maximum coolant temperature I measured (117ºC) and the standard thermostat opening temperature (105ºC) is also around 13ºC, so maybe that is the normal difference between the two? The electric thermostat heater is activated by the engine management system when the engine is under higher loads to force the thermostat to open at a lower temperature.

Phil

Thanks again Phil.

I'll keep an eye on transmission coolant temperatures, as if I'm reading it right your transmission coolant temp was around 110c after 26 minutes of mixed speed driving and you say that's fine, with mine reading 106c.

When I was monitoring the trans oil temp on my journey yesterday, there didn't seem to be any rapid jump in temperature it was a steady climb after warming up and driving. (by the way what diagnostic tool did you use to collect the data and create the graph?)

I will also carry out the trans oil change due to it getting so hot, hopefully next weekend after it's delivered and I get some time.

If there's any further issues then I guess I'll change the oil cooler thermostat, and then cooler if that still doesn't fix things.

Quote:

(by the way what diagnostic tool did you use to collect the data and create the graph?)

Back in the day (15+ years ago), the diagnostic kit to have for the L322 was the Blackbox Solutions Faultmate MSV-2 Extreme, which cost around £925 (& that's when £925 was a lot of money ). This was the kit that I used for my Range Rover diagnostics and it produced .csv files for live data which could then be plotted in Excel.

Phil

Wow that's an investment, very nice

I think I'll stick with my icarsoft for the time being

AFAIR there are three coolant sensors and you have to know which one your reading is from...

When I publicised the lower water thermostat mod it reduced my gearbox temp to well below 100c...

At the bottom of the main radiator is a manifold for the gearbox cooler, what it doesn't say in the manual (well I never found it) is that there is another thermostat within the manifold which controls the temp of the gearbox oil...

From the workshop manual.

The fluid cooler is located at the bottom right hand corner of the engine. The cooler is cooled by engine coolant which
flows in a water jacket around cores within the cooler body. Transmission fluid enters the cooler and flows through
the cores where it is cooled by the engine coolant. The fluid leaves the cooler and is passed back to the transmission.
The transmission fluid is pumped through the cooler by the transmission fluid pump.
The fluid cooler has a thermostatic valve which is opened by transmission fluid temperature. The thermostatic valve
is opened at a transmission fluid temperature of 80°C (176°F) and allows engine coolant to flow through the fluid
cooler.


I had a similar fault to yours so I ended up replacing the main radiator, the lower temp mod, the manifold, the trans oil cooler and lines and the gearbox temps dropped...  Pete
__________________________________________________
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Thanks Pete.

I was thinking about changing the thermostat next, (I assume it's this part you are on about PBM000010) that links to the housing that the oil cooler pushes into as that's the next cheapest part at around £60.

Or even perhaps removing the thermostat first, then putting it into a pan like any other thermostat and seeing what temperature it opens, or if it's stuck? If I did that and it works then the money could go to a new BEHR oil cooler instead.