Been loads talked about this recently but no "one place" to find all the info...

From RAVE

The die-cast coolant pump, driven by an ancillary drive belt, is fitted to the timing case cover. It contains the dual coolant temperature sensor and the electrically heated 'map controlled' thermostat controlled by the engine management system.

The map controlled thermostat incorporates a heating element inside a conventional expanding wax thermostat core which enables the engine management system to 'power' the thermostat open when the engine is under full load and/ or high output conditions. This provides sufficient cooling reserve through anticipation of the thermal load whilst allowing the engine to run at higher operating temperatures under part load conditions.

With the engine running, the coolant pump pulley is driven by an ancillary drive belt. When the engine is cold, the thermostat is closed and coolant is prevented from circulating through the radiator. Coolant is able to circulate through the engine and the passenger compartment heater matrix via a thermostat bypass.

As the temperature increases the thermostat begins to open, allowing cool fluid to be drawn from the radiator bottom hose through the pump and into the cylinder block and hot coolant to flow from the coolant pump housing to the radiator via the radiator top hose, where it is cooled by air passing through the matrix.. When the thermostat opens fully, the full flow of coolant passes through the radiator.

Coolant is also drawn through the liquid cooled transmission fluid cooler and the liquid cooled alternator housing by the coolant pump via the coolant circuit.

So as you can see, not only does the coolant cool the engine, it cools the gearbox as well, when BMW decided to use the then pretty old M62 V8 in the FF they had to meet stricter emissions, the only way they could get the engine to pass part throttle emissions was to make it run much hotter than it was originally designed to do, the thermostat actually starts to open around 105 deg C and is fully open at 113 deg C which is way hotter than the 75-80 deg most engines run at. This creates a massive amount of under bonnet heat and cooks everything under there, reducing the life of rubber and making all the plastic hard and very brittle... not to mention the extra pressure generated in the system, one weak spot is the plug to the electrical thermostat, the seal fails and coolant is forced into the electrical plug and, believe it or not, follows the easiest path which is up inside the wires and into the engine ECU in the electrical box in the engine bay, this corrodes the ECU and causes all sorts of problems. This can still leak with the stat removed so don't plug it back in, just tuck it behind facing downwards so any moisture can drain. This does log a fault with the engine ECU but it is a soft fault and DOES NOT illuminate the check engine light (MIL) It is not a sensor, just a switch so it doesn't effect anything else.

As for cooling the gearbox, well at those temps for any length of time, ie in slow traffic or off roading then the heat soak to the gearbox ups the temp and causes even more issues...

I decided to do something about the temp in mine and came across this mod to allow you to use "normal" thermostats..

I fitted the kit available on eBay from sebastian_workshop_2011 from the Czech Republic, the heading for the listing is

80�C Thermostat kit BMW E39 540i 535i E38 740i 735i X5 M62 - Reduce temperature

This is currently �58.98 delivered to the UK and comes with everything you need...

You have to remove the original thermostat and modify the housing to fit the parts...

The thermostat is removed by removing the lower radiator hose from it by prising up the metal retaining collar and pulling the hose off, remove the wiring plug to it and then four 10mm bolts and remove it from the FF

You then remove the rubber "O" ring and cut off the two alloy lugs shown in the picture with a dremel or hacksaw





Grind/file the lugs down until they are below the level of the mating surface, run a straight edge across the face of the part and ensure what remains of the lugs is lower... The two parts on the right are the remains of the old thermostat and they go in the bin... You may have to file/grind a bit more off for the bleed nipple on some thermostats, but this will be obvious when you try to put it together, the one I have in at the moment doesn't have a bleed nipple...

Click image to enlarge

A great write-up Pete.
I've done the mod as well, and can vouch for its effectiveness, and simple fitting. It's harder to understand, without your pictures, so, this shows what we need to know. And we can always return to stock, if we were in any doubt.

Brilliant Pete, that's taken a lot of the mystery and apprehension away for me.

Even though I've just forked out for a new standard thermostat I've just ordered one of these mods as I was never really happy at the strain the higher temps were placing on all of the connected systems.

Thank you Pete

Regards ______________________________
Simon
______________________________

Range Rover Classic 3.5 efi - Gone
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Land Rover 110 3.5 - Gone
Range Rover P38a 4.0 SE - Pleased it's gone
Range Rover P38a 2.5 DHSE - Just sold
Range Rover L322 4.4 v8 Petrol - Current

Pete, you simply ROCK!

thanks l=Oo\________/oO=l l:OolΞΞΞΞΞΞΞloO:l

Current
RANGE ROVER Vogue 4.4L SDV8 - 2013 - Indus Silver, on Almond.
RANGE ROVER Vogue 4.4L V8 - 2002 - ex-2003 G4 Challenge Event Vehicle, Stage 3: Australia
RANGE ROVER HSE 4.4L V8 - 2004 - one-of-one Overfinch
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Previous:
RANGE ROVER Vogue 4.4L TDV8 - 2012 - RANGE ROVER 3.6L TDV8 x3 - RANGE ROVER Td6 x1 - RANGE ROVER Classic 3.5L V8 x1

Yes great info Pete,something I will certainly concider

Hi Pete,

A quick question regarding this mod, do you remove the o ring and leave it off or do you use it in conjunction with the paper gaskets?

I think I know the answer but would like to hear from someone whose been there and done that...

Cheers ______________________________
Simon
______________________________

Range Rover Classic 3.5 efi - Gone
Range Rover Classic 3.9 efi - Gone
Range Rover Classic 4.2 LSE - Sadly gone
Land Rover 110 3.5 - Gone
Range Rover P38a 4.0 SE - Pleased it's gone
Range Rover P38a 2.5 DHSE - Just sold
Range Rover L322 4.4 v8 Petrol - Current

I reused the O-ring. Regarding not using sealant on the paper gaskets, my kit came pre-assembled. Had it not, I would have used sealant. Mine is weeping very slightly at the paper gaskets. Ron B. VK2OTC
2003 L322 V8 Auto
2007 Yamaha XJR1300
Previous: 1983, 1986 RRC; 1995, 1996 P38A; 1995 Disco1; 1984 V8 County 110; Series IIA

Ok, thank you.

I thought to use it as there isn't much in the way of metal on the thermostat housing.

Cheers ______________________________
Simon
______________________________

Range Rover Classic 3.5 efi - Gone
Range Rover Classic 3.9 efi - Gone
Range Rover Classic 4.2 LSE - Sadly gone
Land Rover 110 3.5 - Gone
Range Rover P38a 4.0 SE - Pleased it's gone
Range Rover P38a 2.5 DHSE - Just sold
Range Rover L322 4.4 v8 Petrol - Current

Yep, use the "O" ring again without a gasket at that end, gasket goes between the three leaves and another against the water pump.

p38arover, I would imagine something has been damaged or you have a burr, run a fine file over all the mating surfaces to see if you have some high spots, mine has been off and on quiet a few times and the gaskets are getting very "used" looking but still seal fine..

Nothing wrong with using a SMALL bead of silicon on them if needed though, just be careful you don't use too much and it gets squashed out inside the water way, this can come off and jam the thermostat or get stuck in the smaller pipes that go to the gearbox cooler. A very small bead around 1-2mm is all that should be needed.

You will probably find you need a new gasket if you ever take it apart again as the silicon will stick the surface of the gasket to the alloy and the gasket rips as you remove it...  Pete
__________________________________________________
2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
-Click for Project Fatty off roader-

Good man, thank you very much ______________________________
Simon
______________________________

Range Rover Classic 3.5 efi - Gone
Range Rover Classic 3.9 efi - Gone
Range Rover Classic 4.2 LSE - Sadly gone
Land Rover 110 3.5 - Gone
Range Rover P38a 4.0 SE - Pleased it's gone
Range Rover P38a 2.5 DHSE - Just sold
Range Rover L322 4.4 v8 Petrol - Current

Pete,

I must thank you on 2 counts, first on a great write up that clarify any doubts anyone would have about tackling this job, and secondly for recommending this mod, I finally got around to fitting mine this afternoon and I agree completely with your comment about engine behaviour afterwards. I took mine out to get warmed up properly prior to letting in go cold for a coolant check and it was as you say more 'relaxed' it settled down to a quieter smoother tickover and seemed smoother throughout the Rev range. Below are some pics of mine in progress and fitted.
Luckily no corrosion in thermostat plug.

Yes. it's a weird sensation.... Pete
__________________________________________________
2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
-Click for Project Fatty off roader-

Good find Pete, Got a question though, even at the coldest we don't even come close to single digit temps in centigrade and in summer high 40s or even 50C, it was 45C-ish todayi, and since you mentioned you ran without a T,stat for months, I'm thinking of getting rid of it althoghter, one less thing to worry about.

I know it will take longer to warm up but here in these temps it doesn't take more than a few minutes to reach temp.

So what you think, good idea or .............. !!!!!!

There is the argument that it may effect the flow in the system which "could" cause problems, in reality I don't think it would make much difference, if I were you I'd give it a go, it doesn't take long at all for it to get upto temp in the summer here so I can't see it's an issue there....

Make sure your viscous fan is working properly, stuff a newspaper in it when the engine is fully warm, if you get confetti then it's fine... Also check the elec fan infront of the rads is working OK as this is used by the aircon AND the engine if the temps get high...  Pete
__________________________________________________
2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
-Click for Project Fatty off roader-

Hey Pete why this mod vs just using a 740D thermostat?