[Dave_3]

I've seen quite a few posts about coolant temperatures on the 335D - mostly in regards to EGR and main thermostats. Some as high as 90+.

What is the factory defined operating temperature for the coolant ? Does anyone know what the defined range is, rather than observed values ? And is it the same for pre and post ED variants ?

D.

[shane55]

Since I replaced both my stats it runs 88-91 constantly, so I'm guessing as both parts were new this is the design range.

While DPF regenerates the temps climb to the high 90's

Shane

[briers]

I dont know Dave

All i can offer is provided the coolant is kept above 78 the DPF will continue to function.

I also replaced my stats and now achieve 91c every journey. It warms within 10mins to regen temps (low 80s) and it will take a further 5 mins to reach 91c.

If the car is taking longer to warm up but is still achieving > 78c you still may have DPF issues if you don't drive it for long enough.

I know you are probably aware of this

The only other thing i heard was BMW didnt put a temp gauge on the 335D because it can vary so much. It can range from 78c to 90c when doing a regen so such a fluctuation is either going to alarm customers and create unnecessary panic or BMW would build in a buffer which is just pointless.

[superflyguy9]

Mine showed reduced fuel economy dropping from 40's to 33mpg. Hidden menu showed it was barely reaching 55 degrees home to work and 65 degrees work to home (35 minute journey mainly motorway). Replaced egr thermostat - shot up to 77 degrees. Two weeks later (delay due to bad weather) replaced main thermostat. Never got above 80 degrees except when regen.

Now stays around 65 degrees some 6 weeks later - lesson? dont buy these parts from eurocarparts. Got a BMW egr thermostat on its way I will update with the results. Will probably have to go through the changing the main stat also......

I know the temp sender range is working (ie is not faulty) because it does reach the magic 90 degrees when doing a regen. So I am aiming to replace parts until I achieve the quoted 90 degrees. As above the DPF is the main worry...

[confused.com]

mine reaches 83/84 on a long motorway drive, i checked it yesterday. In traffic it can tip 90. I'm thinking of getting them both changed to be on the safe side - does anyone know what i should be paying, parts and labour?

[Jules59]

Originally Posted by Dave_3

I've seen quite a few posts about coolant temperatures on the 335D - mostly in regards to EGR and main thermostats. Some as high as 90+.

What is the factory defined operating temperature for the coolant ? Does anyone know what the defined range is, rather than observed values ? And is it the same for pre and post ED variants ?

D.

All I can say is that my remapped 330D runs 92-98C, which is pretty normal for these engines I'm told. Certainly 85C is too cold for a diesel to be efficient IMO. Both my Skoda VRSs all ran 90+ with and without re-maps.
Whats your MPG like? Its often poor if the diesel runs cool.

[coopersim]

Originally Posted by confused.com

mine reaches 83/84 on a long motorway drive, i checked it yesterday. In traffic it can tip 90. I'm thinking of getting them both changed to be on the safe side - does anyone know what i should be paying, parts and labour?

Autodata states a couple of hours labour, plus about £80 for genuine parts (other members have mentioned not to bother with non genuine stats)

I ordered parts; 11517805811 £40.24, 11717787870 £29.94, 83192211191 Antifreeze £8.70 (this is for a 325d)

[NotNormal]

89 to 92 for regular driving, 97 to 98 when regen is occurring

[coopersim]

Just driven my 325d briskly to work about 25 miles, very briefly hit 81, sat at 79 most of the way

[NotNormal]

Originally Posted by coopersim

Just driven my 325d briskly to work about 25 miles, very briefly hit 81, sat at 79 most of the way

You need to replace the thermostat on the EGR cooler first, then run the car and see, if that doesn't work you need to replace the main thermostat behind the main core of the EGR cooler

Tom

[superflyguy9]

Originally Posted by NotNormal

You need to replace the thermostat on the EGR cooler first, then run the car and see, if that doesn't work you need to replace the main thermostat behind the main core of the EGR cooler

Tom

I would say EGR thermostat is working (opens around 70 degrees) - sounds like main stat has gone weak as that should stay closed until 90 degrees. I have read a lot of posts and thats how I understand it....I think

[NotNormal]

Originally Posted by superflyguy9

I would say EGR thermostat is working (opens around 70 degrees) - sounds like main stat has gone weak as that should stay closed until 90 degrees. I have read a lot of posts and thats how I understand it....I think

You can't look at it like that.

If the EGR stat isn't closing properly the it's not letting the flow of coolant be held at the main stat, it acts as a bypass route

So, again, the cheaper option is to replace the EGR stat first as it's cheaper (around £12) and an easy DIY as you won't lose any coolant) then if that stat change doesn't cure it replace the main one !

[coopersim]

I'm going for broke, I've got both, I'm doing that and the glowplugs, hopefully on Thursday if the weather is ok, I'll do the photos and write up - I doubt it will be a hugely different job to a 335d?

[NotNormal]

Originally Posted by coopersim

I'm going for broke, I've got both, I'm doing that and the glowplugs, hopefully on Thursday if the weather is ok, I'll do the photos and write up - I doubt it will be a hugely different job to a 335d?

Almost an identical job

The glow plugs are easy, just time consuming removing all the plastics, whilst you have the inlet off remove the swirl flaps too

I now it's not essential, but it made positive improvements to the power delivery and drive of the car (335d) once the ecu had adapted (somewhere between 1 and 2 tanks of fuel)

[jasonprice07]

83deg on mine.
Car is going in to dealers tomorrow for a coolant leak so may ask them to look at this as well.

Jason

[Dave_3]

Thanks for the feedback.

Mine was hovering around 79-81 after a good half hour of driving, so perhaps slightly low.

D.

[HighlandPete]

Originally Posted by Dave_3

I've seen quite a few posts about coolant temperatures on the 335D - mostly in regards to EGR and main thermostats. Some as high as 90+.

What is the factory defined operating temperature for the coolant ? Does anyone know what the defined range is, rather than observed values ? And is it the same for pre and post ED variants ?

D.

The main thermostat is rated at an opening temperature of 88C, hence the 88 - 92C working range we see in typical use. The same thermostat, as used in the Rover BMW M47R 2.0d engine is rated at 88C +/- 5C tolerance. BMW don't seem to declare that data for the BMW models.

EGR thermostat has twin stage elements, first stage 70C opening temperature, with restricted flow, and full flow (second stage) at 90C, to follow the main thermostat opening temperature. Otherwise (as another post states) the faulty EGR thermostat flow by-passes the main thermostat control and chills the engine, and/or prevents efficient warm up and optimum ECT.

If an EGR thermostat opens pre main thermostat (88C), assuming the main thermostat is still in tolerance, the engine will not reach peak ECT in normal use. Although it may still exceed 90C during a regeneration, as there is typically much more heat in the engine.

HighlandPete

[coopersim]

Ok so mine's not a 335, but the 325 hit 89 today as part of the regen, does that mean I shouldn't change the stats? I thought if the car wasn't running hot enought the dpf wouldn't regen.

[NotNormal]

Originally Posted by coopersim

Ok so mine's not a 335, but the 325 hit 89 today as part of the regen, does that mean I shouldn't change the stats? I thought if the car wasn't running hot enought the dpf wouldn't regen.

you need to change the stat/stats, your cars operating temp should be 89.
One or both of your stats require changing.

There are allot of factors involved with DPF regen, you may have just triggered enough of them to get a regen cycle.

[superflyguy9]

Originally Posted by HighlandPete

The main thermostat is rated at an opening temperature of 88C, hence the 88 - 92C working range we see in typical use. The same thermostat, as used in the Rover BMW M47R 2.0d engine is rated at 88C +/- 5C tolerance. BMW don't seem to declare that data for the BMW models.

EGR thermostat has twin stage elements, first stage 70C opening temperature, with restricted flow, and full flow (second stage) at 90C, to follow the main thermostat opening temperature. Otherwise (as another post states) the faulty EGR thermostat flow by-passes the main thermostat control and chills the engine, and/or prevents efficient warm up and optimum ECT.

If an EGR thermostat opens pre main thermostat (88C), assuming the main thermostat is still in tolerance, the engine will not reach peak ECT in normal use. Although it may still exceed 90C during a regeneration, as there is typically much more heat in the engine.

HighlandPete

Ahaaaa....didnt realise the EGR stat was two stage hence my confusion thanks Pete. So how do the gearbox stats interfere with all this....are they too set at 88 degrees hence if they fail it gives similar symptoms to a failed EGR stat? Just trying to figure out exactly what is wrong with mine. Now on second EGR stat and already replaced main stat - will give it a proper run tomorrow but early signs are again similar - rockets up to 50 degrees then struggles up to 75, then seems to go up and down from there but never getting past 80

[HighlandPete]

Originally Posted by superflyguy9

Ahaaaa....didnt realise the EGR stat was two stage hence my confusion thanks Pete. So how do the gearbox stats interfere with all this....are they too set at 88 degrees hence if they fail it gives similar symptoms to a failed EGR stat? Just trying to figure out exactly what is wrong with mine. Now on second EGR stat and already replaced main stat - will give it a proper run tomorrow but early signs are again similar - rockets up to 50 degrees then struggles up to 75, then seems to go up and down from there but never getting past 80

Two stages, but either element can start to fail in the open position, this allows the short circuit of coolant from the radiator and into the coolant flow. Problem is if they fail, flow can start from ambient temperature so very long warm up and if opening completely at a low temperature enough coolant flow to prevent normal ECT. Even from a a gravity feed, there can be a flow of at least 3-litres a minute, through a partially open EGR thermostat. That is a lot of heat loss, particularly from low ambient temperatures.

From a couple of EGR thermostats I 'dissected'.






NOTE: A faulty auto gearbox oil cooler thermostat can do the same, it also can by-pass the main thermostat, and allows cold coolant directly from the bottom of the radiator into the circulating flow.

Oil cooler thermostat is part of the heat exchanger, so a costly repair.


HighlandPete

[superflyguy9]

Originally Posted by HighlandPete

Two stages, but either element can start to fail in the open position, this allows the short circuit of coolant from the radiator and into the coolant flow.

Makes sense. I have changed the EGR thermostat TWICE now in the last 2 months without any positive results, today on an 18 mile journey (mainly motorway) engine temp didnt get above 63 degrees, seemed to shoot up to 43 then sit at 50 for a long time before gradually creeping up. Therefore I should probably rule out the EGR thermostat as being the problem.

I changed the main thermostat about 1 month ago too, as that seemed to be the natural progression with this reoccurring fault.

Originally Posted by HighlandPete

NOTE: A faulty auto gearbox oil cooler thermostat can do the same, it also can by-pass the main thermostat, and allows cold coolant directly from the bottom of the radiator into the circulating flow.

Oil cooler thermostat is part of the heat exchanger, so a costly repair.


HighlandPete

So I am screwed then - as it sounds like this is the only thing left to do?

One chap mentioned the "Top Hose Thermostat Modification" in a previous post and that worked successfully- as I undertand this is inserting a "Thermostat" into the top hose preventing any Bi-pass situations. I searched and searched for this but couldnt find the spec or DIY on how to do this and with what parts - or is it safe to do versus the "costly" gearbox heat exchanger repair?

Is there anything else I can do / try to diagnose my low coolant temperatures Definitively??

Thanks again for your help