I only do it if there's no other way-most of the time the cat gets it's normal run around the block to warm up in the normal way

 

My concern wouldn't be direct or immediate destruction of the transmission. Rather, I'd be worried about overheating the fluid with 5 minutes of brake-torquing....and the long term results of same.

Anyhow, do what you like :-).

I must say, though, that describing a technique as "brutal" from one side of your mouth (and adding a "...at your own risk" disclaimer to boot) and then defending it as a perfectly harmless practice from the other side seems a bit contradictory to me!

Cheers
DD

 

Brake-torquing at 1200rpm for 5 minutes on a stone-cold gearbox & engine at around freezing point or below is unlikely to overheat the fluid, as it passes through the transmission oil cooler in the radiator anyway, which then dissipates the heat to the coolant-so you can see by the coolant temperature gauge how fast the temp is rising with the added heat from the transmission fluid, even with the 'dead' portion of the X308 temp gauge in the centre.

Once the temp has moved off the stone-cold blue area & is around quarter gauge deflection, then I gradually drop the engine speed back to idle.

I don't recall describing the technique as harmless-simply that it's not blown up any of my engines or gearboxes. The 'disclaimer' is simply that it's an observation & write-up I made of a technique used on my own car-not a direct recommendation for others to do the same as me

Stall-speed tests are often done to diagnose torque converter/transmission problems anyway-the technique there is to do the test on a fully-warmed up engine & gearbox & is far more 'brutal' as you run the engine up to full throttle against the stationary turbine on a hot powertrain-not just light throttle on a cold powertrain.

Under those circumstances with a hot powertrain & a full throttle brake-torque load, the method is to not to exceed 10 seconds at a time for each 'burst' of power at the stall speed, and then to let the powertrain cool down again for several minutes before any further full-load stall tests.

The thermal load on the powertrain of a fully warmed-up engine/gearbox which is then run up to maximum torque converter stall speed at full throttle, is much greater than using part-throttle with a stone-cold powertrain, yet this is a common technique for diagnosing torque converter faults & is described in many workshop manuals-with the necessary provisos for avoiding fluid overheating.

My method is a 'half-way' house that I occasionally use, as it provides more load to the engine while avoiding the much heavier stress of a full-on stall speed test at full throttle on a hot engine.

I once used this method of measuring converter stall-speed to increase the power of my old BMW diesel by increasing the fuelling & then doing short measuring bursts of full-throttle stall speed tests to check the increase in converter stall-speed, commensurate with increased engine power.

If you think that what I do to the XJR is brutal, you should have seen how I 'tuned' the Diesel BMW for more power

I then did another 60k miles on the BMW, which now has 176k miles on the original gearbox & that is still working fine-the fluid is still reddish-brown with no burnt clutch material.

As before, this is not a 'recommendation' for others to do the same thing-merely an 'observation' & description of a certain method I use on certain occasions to achieve certain results...

That concludes the case for the defence, M'lud

 

Overall, the technique seems to be well thought out and based on a sound knowledge of the systems involved. Some factory manuals point out that one of the purposes of a shared coolant and ATF cooling assembly is to share the heat to bring the ATF up to operating temperature more quickly. Reality sometimes impinges on the ideal and knowing how to deal with it is just one more survival skill.

The only caveat is that the differential is still stone cold no matter which way the car is warmed up, or if the car is warmed up at all. The same applies to the front wheel bearings. So, for the first drive of the day, I like to warm up to the end of the blue zone, and the drive gently for the first few minutes.

The proceedings are hereby stayed.

 

I did a lot of measurements for this technique using certain hidden features of BMW trip computers that I unlocked. One of these hidden functions (used by BMW Technicians) is an instantaneous readout of fuel consumption in Litres per Hour. The following figures show the instantaneous fuel consumption for various powertrain temperature/gearbox load conditions on my 1995 BMW 525tds:


1) Engine idling immediately after a cold start: 1.5L per hour

2) Engine & gearbox fully warmed up & idling hot: 0.5L per hour

3) Full-throttle stall-speed test on a hot powertrain: 30L per hour

4) Part-throttle brake-torqued by gearbox, engine at 1500rpm: 6L per hour


The above approximate figures show that by far the heaviest load comes from the full-throttle stall speed test & the part-throttle method I use only applies around 20% of the thermal & mechanical load of the full-throttle stall speed test.

I only do this 'trick' on rare occasions when it's not practical to take the car round the block to warm it up-yet it still needs to be 'run up' & warmed through if left in the cold & snow for too long. The fully-warmed up engine heats the engine bay & gradually percolates through the bonnet & front wings, heating them up & drying them out.

Most of the time I do take it for a normal drive on the road, but there are odd occasions in winter unique to the parking & climate conditions where I live that mean I use this method instead.

I can assure everyone that I do not make a habit of sitting there every day of the week pouring gallons of fuel in the tank, while the engine constantly labours against a stalled converter turbine for the rest of time while the car goes nowhere

I only use this method on those automatics which can genuinely select a high gear manually from a standing start without defaulting to 1st gear, so the torque to the propshaft & final drive is minimised.

The Defendant has now concluded his speech on the Mitigating Circumstances

 

OK to summarize: Brutal, but not described as harmless, and not a recommendation that others do the same. Got it !





And thoroughly done, I'll have to admit.

There's not enough evidence to convict; no proof that an actual crime has been committed. You're skirting the law at the edges, though.

We'll be keeping an eye on you, mister!

Bailiff, release the defendant!



Cheers
DD

 

Thank you, Your Honour

If my gearbox does subsequently disentegrate, then I'll be re-appearing to plead guilty as charged...

Right, must go & hide those broken cogs quickly before anyone from CSI Liverpool finds them

 

Interesting discussion and quite civil.

Red October- I see you're interested in wide open spaces. Come visit us in Canada were we've got even more land than the US and only 1/10th the population (and no guns).

 

Yup. I love Canada! If you would have preserved the rights of the free citizens to own weapons, I would love to live in some parts of your gorgeous country (some parts are just too cold!),....as it is,...Montana is very close, VERY free, and just as beautiful.

I understand my views are not shared by many, but I am a fourth generation soldier, and a rebel at heart. I speak and shoot straight, and my gun collection is my pride and joy. As long as I can protect my family, my land, and my animals, without depending on ANY government to do it, I feel free. I pay my taxes (we need the infrastructure) to the government, and that's as far as I want them to be involved in MY life.
To each his own.

 

Not interested in getting into a debate about 2nd amendment rights and why someone would want to give bears arms instead of legs, but we most cartainly have the right to own weapons.

Canadian Gun Laws: Weapons Used In Mass Shootings Still Not Prohibited

Just setting the record straight.

 

As Jag owners & enthusiasts, we even like to keep our disagreements civilised

Argument between small hatchback drivers: "I'm going to kick your head in"

Argument between Jaguar drivers: "Sir, I demand satisfaction"


Much appreciate the invite to Canada-I love the wide open spaces, but then I do live in the centre of a small cramped wet Northern English town so I crave space

I go to the Scottish Highlands for therapy in summer-boy, are there some great driving roads there & stunning scenery. Up in the far North, you can drive across the very top of Scotland & on some occasions not see another car for a whole 30 minutes

There's nobody to shoot up there even if you did have a gun-only deer...

 

This is wrong in so many ways, including;
1. heavily loading a cold engine
2. ^^^^^^^^^^^^^ transmission
3. you are straining the engine mounts

Be sure to include this "procedure" in your car's service history when selling it on.

 

Do XJR owners actually sell their cars on? Had mine over 4 years now & no intentions of ever letting it go, unless it gets written off in a crash or goes to the great scrapyard in the sky

 

"I only use this method on those automatics which can genuinely select a high gear manually from a standing start without defaulting to 1st gear, so the torque to the propshaft & final drive is minimised."
You're not mitigating anything as the torque converter and pump are taking the beating, they couldn't care less what gear you've selected. You are less likely to overpower the brakes with less gear reduction but it's no less stressfull for your transmission, etc.
It would also make sense that doing this is also dumping a whole bunch more of that over-rich mixture through your catalysts, another expensive component.
As someone who is sympathetic to machinery this makes me cringe.

 

I had naturally expected this sort of reaction, but nevertheless will add some more technical information to the debate...

Bearing in mind what the XJR powertrain is actually capable of handling when you drive it hard for tens of thousands of miles, year after year, the small amount of 'work' that my quick warm-up method generates for the car is tiny compared to the amount of mechanical work it's done over 12 years & 150,000 miles of hard driving...

I may use this method once or twice a month in the coldest winter months, which may amount to 15 or 20 minutes of 'quick warm up time' every year. As I had explained previously, it's a method I use on just a few occasions.

The XJR gearbox is quite capable of handling the full 387lbf/ft of torque in 1st gear when you repeatedly gun the car away from a standstill at full throttle, year after year, for tens of thousands of miles with hot transmission fluid.

I hardly think that a few minutes of part throttle, low revs on a cold powertrain & fluid is going to amount to a hill of beans in terms of powertrain wear.

Regarding catalysts & over-fuelling, the hotter the exhaust gasses are, the quicker the catalysts warm up to 'light off' temperature & the sooner the engine management system enters 'closed loop' mixture control. Therefore letting the engine simply idle from cold means the catalysts will take longer to warm up & you will be running in 'open loop' fuelling for longer without precise mixture control.

The torque converter 'takes a beating' every time you pull away from a standstill as the engine-driven impeller churns the hot fluid into an initially stationary turbine on the gearbox input shaft, before the car begins to move & the turbine speed starts to 'catch up' with the impeller speed & the stator becomes fluid locked.

Torque converters naturally get hot & take a beating-that's what they're designed to do & that's why the transmission channels the hot fluid to a cooler.

How much of a beating do you think the torque converter takes when it's fed with almost 400lbf/ft of torque from a hot engine with hot fluid & then asked to launch a 1.8 ton car from standstill-year after year, for huge mileages?

A damn sight more than a few minutes a year on a cold powertrain at part throttle...

I have never had problems with cars from working them hard-by far the worst problems have happened when cars are 'pussyfooted' around & not made to work-that's what makes me cringe...

 

While you may very well get away with this you aren't doing the car any favors. As to the cold enrichment; your own experiments indicate a higher fuel flow when stalling the converter on the cold engine. The cats are coping with this.
The other point overlooked is less than ideal lubrication and the different clearances in cold engines and transmissions.
It's your car, sir, do as you please but it is abusive.

 

My own experiments with my BMW did indeed show a higher fuel flow rate after the initial cold start, but the faster it warmed up, the quicker it dropped down to the lower hot engine flow rate.

As explained previously, I do not run the converter up to the full stall speed as I'm aware this would place a much bigger load on the whole powertrain. I run at a part throttle for a few minutes, on perhaps 3 or 4 occasions in a whole year.

After the initial engine cold start, I run at a fast idle with no converter load for around 15 seconds to ensure the oil has circulated properly before applying the load.

The term 'abusive' is a relative one & there's no precise definition. You could choose to define it in terms of the 'fear factor' of potentially damaging something, or define it as an actual measured reduction in the life expectancy of a mechanical component.

Both definitions are hard to define precisely, so I'll go by my own record of countless big-engined automatics which have run to 130k miles, 150k miles, 170k miles & 240k miles without blowing up either the engines or gearboxes...

Whilst a full-on wide open throttle stall speed would indeed put a large stress on a powertrain, I don't come anywhere near that with a part throttle & a low engine speed...

 

Rather than argue degrees of abuse I'll concede that as you describe it this is not drastic.
If you were to measure throttle opening using your method of stalling the converter vs. simply driving off you'll find that you are using a bigger throttle opening, hence more fuel and wear.
I stand by my position there are far better ways of warming up and any competent, credentialed mechanic would agree.
Were this a sound method to either warm the drivetrain or "light off" the cats it would be recommended by the manufacturers as they are behooved to have a brief warm up and lower emissions. Many inhibit gear changes when cold to this end.
Again, you are entitled to do as you wish.
Remind me not to lend you my car.

 

Don't worry-I won't, as mine all work fine...

Most of the time I do just drive off normally, but if you'd read my posts fully then you'll see that this is a method I use on the rare occasions where the car may not have been used for a little while & I don't want to let it sit there all snowed up for too long, while everything ices up & the battery discharges. Due to my location & unique parking situation with my cars, I can't just drive the Jag straight out on the road without first moving one of my other cars from across the driveway.

Now if that's all snowed up as well, then I can't just fire that up for a quick 100m round the block to re-park it while I then take the Jag round the block for a drive, or that will also only be partially-warmed up too.

This quick warm-up method is only ever used on rare occasions when the car's been sitting idle for a long period of time & can't be easily taken out on the road due to the climatic & parking circumstances I've described above.

For the remaining 99.9% of the time, the car does get started & then taken straight onto the road for a normal drive-and I don't come back until the engine has warmed up fully & then been driven at least another 5 or 10 miles on a hot engine, with periods of full throttle & extended rpm.

I'm well aware that the first few seconds after a cold start are where the majority of engine wear occurs, so I run at a fast idle for the first 15 seconds or so before applying the transmission load-and that also applies to when I take the car out on the road.

If we get a winter where there's no snow here, then I don't need to use that method & the car will always be driven straight onto the road & warmed up via normal driving.

I'm also well aware that a 'competent, credentialled' mechanic would not recommend a method such as I use on those rare occasions where I can't easily get it out onto the road to warm it up.

England is a small, cramped country & I for one do not have the luxury of just being able to swan out easily into the wide open spaces with the Jag-I live in the centre of a small town on a busy road where it's quite a procedure sometimes just to get the cars in the driveway out onto the road itself, before we even get to winter & the snow.

Again, I explained this in some detail previously in this thread...

No doubt there may be some in this world who might subliminally hope my powertrain does explode, so the 'I told you so' messages can then be directed my way-but until that moment happens, I shall continue to enjoy my Jag, as I'm sure we all will

 

See post #25 for a summary.

However, the bottom line is that it is his car to do with as he pleases.