Thread: D3 TDV6 overheating on sand?

Originally Posted by Blknight.aus

thats because its a normalised gauge......

if the engine is within the acceptable operating range then the needle points to the middle, once it goes up then you're still not in trouble its still got some ways to go before its dangerous once its in the red your doing damage, fortunately for d3+ the engine derates and shuts down before it gets critical.

The main reasons that normalised gauges with massive swings once the normal operating range then the safe operating ranges are exceeded are because of nufty dipwitted incompetent drivers that wouldnt watch the gauges and wouldnt notice a slow climb of an over heated engine and also because of idiotic drivers who dont read manuals and dont comprehend that an engine has an ideal operating temperature and an acceptable operating range. Yes the engine is going to run up near 105 degrees C (and higher) if youve got a trailer on the back and your hauling it over stocktons and your in high range and you have high tyre pressures its not over heating, its just working harder, you know in the same way that you feel hotter and sweat more If I make you do a run carrying a 30KG pack up a sand dune in summer compared to taking a leisurely stroll on a fine autumn evening along a nice boulevard watching the sunset.

Theres a lot of people who I like to call "you idiot" I'm slowly becoming convinced that people who buy expensive electronic diagnostic tools just to use them as a temperature gauge because the factory normalised gauge "doesnt work" deserve their own special place, much like the special place in hell for child molesters and people who turn their phone to vibrate but still answer it then have loud conversations on it in the movies.

I get thie sinking feeling that in the very near future there will be a spiel on this very topic in the book.

So what I'm hearing is that only the bottom half of the guage works, cos I know it creeps from cold up to normal operating temp?
I get why it might not be linear, so there's higher sensitivity where it matters, but surely to give you no feed back on how hard you're working the engine and then jump to emergency is a bit daft? They could have just had a red light and saved space on the dash...

only the centre of the gauge is Normalised..

So there is a say 10-20c operating range where is sits nice and still...

Over that, it begins to move again, giving warning.

Of course it cant do it for catastrophic failure, only gradual overheating.

Any vehicle under a catastrophic overheat just flicks straight to Red (unless it dumps coolant, then it often doesn't move). Had this in several street cars...

Originally Posted by Stuart02

So what I'm hearing is that only the bottom half of the guage works, cos I know it creeps from cold up to normal operating temp?
I get why it might not be linear, so there's higher sensitivity where it matters, but surely to give you no feed back on how hard you're working the engine and then jump to emergency is a bit daft? They could have just had a red light and saved space on the dash...

no it moves..

(keeping it simple and working from water only numbers in a cooling system that can pressurize to 14psig)
there are generally 4 spots in the gauge... (and potentially many more in the engine management system)

cold-minimum normal here the gauge moves pretty much like an old school temperature gauge (lets say 0-75)
minimum normal-maximum normalHere the gauge does not move it just points to one position, normally right in the middle of the gauge sweep (lets say 75-105)
maximum normal-maximum permissible here the gauge moves very quickly as in a modern ally engine this is a very very short temperature range (lets say 105-119) (119 degrees is about the boiling point of water @14psig)
maximum permissible-overheated. (120+)this is the last bit of the gauge, the little red bit.

The most basic version (without getting into the thermodynamics of fluid phase changes and heat absorbsion) is.

The needle moves very quickly through the max-norm to max permissible range because its the smallest temperature bracket of the 4 and has the largest movement per degree of the system. It can take less than a minute for the engine to get from max normal-overheated. How often are you scanning your gauges?

The slightly more complicated version that deals with heat dissipation is

The whole engine forms part of the cooling system, if your bogging down in sand and are making big power demands from the engine the block+head+ sump get hot, the vehicle speed goes down so airflow through the radiator decreases, simple.

Theres more to it than that however. the block, head + sump all play their part in cooling the engine with more heat coming out of the radiator and less air to move it the whole engine bay starts to heat up. Once this happens the block and head are no longer as effective at getting rid of heat into the engine bay because there is a lower temperature differential between engine bay air and block temp so more load is placed onto the cooling system more load on the cooling system means more heat in the engine bay because of the air being drawn through the radiator.

Dont forget you also have the exhaust (+Turbos) in there heating things up as well the harder and hotter you work the engine the hotter these things get adding to heat load inside the engine bay and in the case of the exhaust direct transfer of heat to the head.

Pile onto that if your digging through sand youve also now lost a significant portion of the airflow out of the engine bay so not only is the fan shifting less air because of loss of forwards speed of the vehicle but its now got less space to push the air it can shift out of the engine bay. Add to that youve now got less clearance to the sump and you start to get radiated heat reflecting back from the sand into the engine bay, oh, and how hot was that sand to start with, that heat wont be helping you any.

now all this extra heat also begins to punch up the cabin temperature so now the aircon works harder, so more drag on the engine to add more heat to the engine bay and just for poops and giggles the condensor for the AC is in front of the radiator so now on top of the extra load from the AC and all the other factors Ive mentioned the air thats coming into the radiator is being preheated by the condenser.

I haven't had the D4 in sand yet so can't comment.

In the D2 when doing a lot of very soft sand work,particularly in hot weather the auto was the first thing to overheat,the engine temp guage never moved.
Then you just let the vehicle idle in neutral,as per hand book recommendations,until the red light went off & then kept going.This didn't happen very often,only occasionally

This is also what happens with a mates late model Paj,but more often than the D2.

Originally Posted by Blknight.aus

The slightly more complicated version that deals with heat dissipation is

The whole engine forms part of the cooling system, if your bogging down in sand and are making big power demands from the engine the block+head+ sump get hot, the vehicle speed goes down so airflow through the radiator decreases, simple.

Theres more to it than that however. the block, head + sump all play their part in cooling the engine with more heat coming out of the radiator and less air to move it the whole engine bay starts to heat up. Once this happens the block and head are no longer as effective at getting rid of heat into the engine bay because there is a lower temperature differential between engine bay air and block temp so more load is placed onto the cooling system more load on the cooling system means more heat in the engine bay because of the air being drawn through the radiator.

Dont forget you also have the exhaust (+Turbos) in there heating things up as well the harder and hotter you work the engine the hotter these things get adding to heat load inside the engine bay and in the case of the exhaust direct transfer of heat to the head.

Pile onto that if your digging through sand youve also now lost a significant portion of the airflow out of the engine bay so not only is the fan shifting less air because of loss of forwards speed of the vehicle but its now got less space to push the air it can shift out of the engine bay. Add to that youve now got less clearance to the sump and you start to get radiated heat reflecting back from the sand into the engine bay, oh, and how hot was that sand to start with, that heat wont be helping you any.

now all this extra heat also begins to punch up the cabin temperature so now the aircon works harder, so more drag on the engine to add more heat to the engine bay and just for poops and giggles the condensor for the AC is in front of the radiator so now on top of the extra load from the AC and all the other factors Ive mentioned the air thats coming into the radiator is being preheated by the condenser.

It's even more complicated than that. Your "runaway scenario" assumes no change in the cooling capacity of the vehicle, which in a correctly-functioning vehicle such as a D3 is incorrect. The vehicle starts employing various techniques to control the build-up of heat, such as (in a D3) increasing the fan rate + the volume/rate of circulating water. In almost all cases, this will interrupt the thermal negative feedback loops you're describing.

A correctly-functioning D3 has more than adequate capacity to keep the engine within the normal operational heat range when driving in most sand conditions. Far more so than previous LR's.

Cheers,

Gordon

Hello
I had the same worries, loss of power, alarm and red on the temperature gauge.
I cut the contact and instantly restarts, everything is normal ...
I change the temperature sensor, everything is normal now!

Could be the water outlet housing. It is plastic and will sometimes leak before actually failing. Common fault with many vehicles with plastiv cooling bits.

so in your opinion the auxiliary transmission oil cooler Davis Performance recommended for towing my CT and sand driving and which I got installed will not be of any benefit ?