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GoNz0

Inline thermostat mod to fix the gearbox heat exchanger write up.

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As a lot of you know I have been trying to fix my overcooling issue due to a knackered gearbox heat exchanger, in the few months of owning my LCI 535d I have got through 7 heat exchangers, the thermostat design at some stage 5 or more years ago was replaced with cheap chinese thermostats that fail the 1st time they open putting you back in the same position you started off with.

Behr make it for BMW, they also sell it under the Hella brand and it is the identical part as confirmed by Steve Hudson who runs the product development of Hella UK, feel free to phone him on 07860 895457 if you had one fail until the guy gets the bloody message!

I had 3 Hella, then had to buy a BMW one for £200 that failed, I had BMW replace it under warranty twice and had to fight for that then they refunded me and left it on the car to wash their hands of the problem. They know the parts have a design flaw and choose to ignore it due to the car not having a temp display, if they did acknowledge the fault it would be a huge recall to sort it but they have no redesigned part to replace it with.

As a last resort I tried a Nissens one, it turns out this was identical to the Trucktec part another guy fitted (yes it failed) and then I found it is the same as a cheap chinese one for £50 so the chance in a working replacement is 0%

 

@Wabby pointed me in the direction of an inline thermostat to work around the problem, the part I used is a VAG part used for 12+ years in various cars from Golfs to the Audi R8. The stat needs to sit just after the heat exchanger to work.

 

The parts needed are the stat, it is part number 4E0121113 and 2 27mm heavy duty spring clamps part number N 90687001

You can either call your local TPS and get genuine parts, the stat costs £26  or ebay it for £20 or £16 for a cheaper part, the clamps will be a couple of quid each, you will need coolant as well, I tend to lose 100-200ml as I clamp the pipes off.

 

I use Irwin vice grips,  a pair costs £8 at the moment at screwfix, great little tool and does a great job stopping coolant pissing out https://www.screwfix.com/p/irwin-quick-grip-6-mini-one-handed-bar-clamp/29139.

 

To get at the pipe to fit the inline stat the car needs to have the front end jacked up on axle stands, the undertray removed. The engine cover off and the slam panel removed to expose the rad and charge pipe.

 

Unscrew the cover on top of the rad, and remove it (5 torx screws) unplug the fan then underneath again pull the coolant pipe off the bottom of the fan shroud and clamp it off to stop coolant coming out the heat exchanger, unclip the charge pipe from the intercooler to the throttle body making sure you take the temp sensor wire off, you can then remove the charge pipe from below, if that pipe has oil on the outside you need new seals from BMW. With the charge pipe off you can lift the fan out from above. You now have room to work.

 

The pipe we are going to fit the stat in is the one running down to the front of the heat exchanger, clamp it off as close to the top as possible then go under the car and pop the clip out so you can remove it, put a catch try under the car as coolant will come out when you pull it off, this is the view from above.

 

22AKKi3.jpg

 

You will be taking out 50mm, as it happens the width of a wide roll of masking tape as you can see. Offer up the new stat and make sure you are happy that it is far enough up so it doesn't touch the elbow fitting, I think I went up about 60-70mm, measure twice cut once or you will be spending £60 on a new pipe, once happy cut out the 50mm section.

 

Time for a cuppa but fill the kettle up as you will need hot water to soften the pipe. Start with the small section that connects to the exchanger and heat it up, grab some neat coolant to act as lubricant.

 

This is the stat pointing up, it has a direction arrow and the flow comes from the exchanger up to the T connector that take it to the water pump

 

DZmp74N.jpg?1

 

Get a 27mm clamp and put it over the metal band on the elbow so it is out the way and ready to slip up into place once the pipes on.

It is not easy getting the pipe in so I suggest you initially push the stat in upside down as this will let you hold the main housing and not the removable part ( I managed to rotate the fitting and caused it to leak so I had to take the bastard off to put it back together), push it in with some coolant to help then set it aside for 5 minutes while you finish your cuppa. Once it has cooled down it will have expanded so you can pull it out and fit it the right way up then move the 27mm clamp over the fitting, at least you can do this step off the car.

 

Now you can fit the other side to the other part of the pipe, you only need to do it once this time. Slip the 2nd 27mm clamp up the pipe and push the stat into the pipe, once it is all the way down check the elbow lines up with the exchanger, if not twist it from the top so you can use the housing as a grip and once happy slip the clamp over ( I used mole grips to expand the clamp)

 

Now you can fit the pipe back to the exchanger and remove the clamps. 

 

kgGaBO5.jpg

 

 

 

Refit the fan (check it hooks on at the bottom or it will flap about and trash everything) and plug in the power, clean the charge pipe seals (or replace them) and lube with engine oil then refit the charge pipe and plug to the temp sensor.

Now is a good time to remove all your tools and fire up the engine to check for leaks and top off the coolant, once happy carry on putting the car back together.

 

Refit the top cover for the rad and 5 screws followed by the slam panel and engine cover, clip the pipe back into the fan shroud from under the car and check the pipe fittings are secure, double check everything then refit the undertray.

 

Check the coolant level then you are finished and the next day with a cold engine.

 

 

Credits to @Wabby and @Clavurion for pointing me in the right direction.

 

 

Edited by GoNz0

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I went for a drive to meet a member of the 5 series facebook group to run diagnostics on his car, after 6 miles of slow driving miss daisy driving I was up to 88, the gearbox hit 30 within minutes then climbed to mid 60's at the end of the 11 mile drive.

On the drive back I managed to get some open road and snot it, the gearbox went to mid 70's, when I get the excuse to go for a long drive I will monitor the gearbox temps to make sure they stay below 90

 

My results when I got back home. Engine oil temp is actually coolant temp, either that or for some reason they both stay the same as the hidden dash display!

 

LWtQZm4.jpg

Edited by GoNz0

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Reserved for instructions on removing the heat exchanger valves if you want to do that as well, it isn't necessary but mine was sealed closed after messing about with it. 

Edited by GoNz0

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Phone 1st. Euros sell a completely different part when you give them that number and the TPS near them didn't have one so I had to drive to Nottingham to pick it up.

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Went out for a spin tonight, bit of town driving, blast down the bypass, stopped for a chat then went back via the M1 for a stop. Car sits at 91 engine and 71 gearbox on the M1 at 75. On the last leg I sat going between 2nd and 3rd in manual mode over and over to work the box and it got to 83, couldn't be arsed to keep at it as I had cold beer in the fridge.

 

I will report back after the rush hour fetch the Mrs run the next time she is in the office, may be a week or more though, I may try and time it for rush hour when I take the heat exchanger back for refund though.

 

 

20180414_213218.jpg

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Anyone else done this yet?

 

A guy off the facebook 5er group reported back after a few days saying his temps are bang on, he also mentioned he had a bit of an emergency where he ended up on the motorway with the needle "off the clock" followed by lots of roundabouts to his destination, gearbox never went over 85c :ph34r:

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As an addendum to this, my car just went for it's MOT but the tester was unable to get the engine oil above 50c (this after a 20 mile drive to the station in question)

 

It did pass it's emissions though. 

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1 minute ago, Dotcom1970 said:

As an addendum to this, my car just went for it's MOT but the tester was unable to get the engine oil above 50c (this after a 20 mile drive to the station in question)

 

It did pass it's emissions though. 

Haven't you done this fix yet?

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1 minute ago, GoNz0 said:

Haven't you done this fix yet?

 

Not yet - it's being done in a week or so whilst I'm having the service done along with a few other bits

 

Edited by Dotcom1970

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5 minutes ago, Dotcom1970 said:

 

Not yet - it's being done in a week or so whilst I'm having the service done along with a few other bits

 

Good stuff, mines been rock solid since, gearbox warms up but doesn't go over 85 :)

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Just now, GoNz0 said:

Good stuff, mines been rock solid since, gearbox warms up but doesn't go over 85 :)

 

That's great to hear :)

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Hi GoNz0

 

Is your car still running ok , in the location and direction where you mounted the inline thermostat. I am having similar of car not reaching temp. | have changed Main and EGR thermostats with Genuine BMW parts.  And now the temperature gets up to 82 if setting out in clear roads. But if i get stuck in traffic it will reach 92 and stay there.  So now i suspecting the Gearbox cooler thermostat and i have read your investigations on flow and the best place to mount the inline.   I have come across a  German article http://djoos.de/bmw-temperaturprobleme-thermostat-und-waermetauscher/   . The only difference is he has mounted the thermostat after the cooler on the return flow (pic copied from site)...  ( this does look easier to install without removing all the slam panel and fan) .  Now you have been running for a while , do you think it would make that much difference where it is mounted, obviously it will be cooler on the return after the cooler, but if closed will heat and open. (dont want to risk over heating the box)

 

Inline-Thermostat_2.jpg

 

 

Edited by bdurrant
spelling

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As was pointed out to me the guy who did a similar mod got it very wrong and obviously didn't force the box to overheat or he would be in the shit, he thinks the flow runs the other way and the way he has done it would be the same as sticking a plug in the pipe as the only way it will open it if the rad ever got to 80 on the cool side (not going to happen with the cooling setup) as that pipe is the feed pipe not the return pipe.

Putting the stat where I did is perfect, cool coolant is drawn from the rad through the cooler where it picks up the gearbox heat and once the gearbox gets to 85 degrees it mixes enough to start the stat opening at 80 (the pinhole to allow flow is the reason why you need a stat rated lower than the main one of 92 as it is mixing pre cooled coolant if that makes sense)

I have not got my box over 85 and the car sits happily at 88c or above.

 

The other guy I was talking with who is a mechanic did the same mod just after me and did what he called a blue light run where he thrashed the tits off the car (off the clock) on the motorway followed by ragging along a ring road with islands dotted about to the box was pushed to the limit (his car is tuned as well)

 

He has his better half monitoring it and it never went over 85 monitoring the gearbox.

 

Look at your rad, the top pipe is the return on the right standing in front, the pipe he has used comes from the cool side.

 

Yes it is a little harder to put it where I did but you have no other option as that is the return side. TBH once you pull the pipe off the cooler with the fan out the way you can bend it up and using a clamp like I did keeps it pointing up out the engine bay so you can do the work.

 

 

 

 

 

 

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17 minutes ago, bdurrant said:

Hi GoNz0

 

Is your car still running ok , in the location and direction where you mounted the inline thermostat. I am having similar of car not reaching temp. | have changed Main and EGR thermostats with Genuine BMW parts.  And now the temperature gets up to 82 if setting out in clear roads. But if i get stuck in traffic it will reach 92 and stay there.  So now i suspecting the Gearbox cooler thermostat and i have read your investigations on flow and the best place to mount the inline.   I have come across a  German article http://djoos.de/bmw-temperaturprobleme-thermostat-und-waermetauscher/   . The only difference is he has mounted the thermostat after the cooler on the return flow (pic copied from site)...  ( this does look easier to install without removing all the slam panel and fan) .  Now you have been running for a while , do you think it would make that much difference where it is mounted, obviously it will be cooler on the return after the cooler, but if closed will heat and open. (dont want to risk over heating the box)

 

Inline-Thermostat_2.jpg

 

 

 

That's the feed hose from radiator to heat exchanger. That thermostat will never open. Though solves the problem for engine temp but gearbox oil has no cooling at any temp.

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If you translate that page the 2nd reply points this out as well :)

 

 

 

 

 

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1 hour ago, bdurrant said:

thanks . i shall stop being lazy and fit in correctly :-)

 

Honestly m8, it is no more work and the bonus is you get to work on it from above (yes I know you could take the other pipe off but then you have to replace a load of coolant)

 

Just get a pair of clamps to keep coolant loss to a minimum and you only need a 1lt bottle of G48

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I'm toying with the idea of buying a complete new hose assembly for this, as I have to replace both the waterpump and thermostat, and experience with the E39 suggests it's a sensible precaution to replace all the hoses anyway, so i might as well start now.  If the engine was a petrol, I would have also considered moving to waterless coolant such as Evans Power Cool 180, but don't think it's worth the £200 or so to do the conversion.

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Has someone been buying up the Vaico V20-1320 replacement coolant hose in the UK for this mod?  Out of stock everywhere :lol:

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44 minutes ago, Dotcom1970 said:

Has someone been buying up the Vaico V20-1320 replacement coolant hose in the UK for this mod?  Out of stock everywhere :lol:

Autodoc should have them m8, last thing I got off them was cheaper than the UK with the £9 shipping!

Try Amazon as well, I have had a couple of things off there from Amazon direct cheaper than autodoc, my brake servo and the AUC sensor.

Edited by GoNz0

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1 minute ago, GoNz0 said:

Autodoc should have them m8, last thing I got off them was cheaper than the UK with the £9 shipping!

Try Amazon as well, I have had a couple of things off there from Amazon direct cheaper than autodoc, my brake servo and the AUC sensor.

 

Tried both of those, OOS!

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It won't be more than £65 from Cotswold if you have to go the dealer route.

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4 minutes ago, GoNz0 said:

It won't be more than £65 from Cotswold if you have to go the dealer route.

 

Yeah, the OEM part shipping from Latvia is about that price also

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