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Full Version: Winter Thermostat For 0.8 Cdi Engine?
Club smart Car > Technical Discussions > Operation and Maintenance: 450 Model, 2005-2006, diesel
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tolsen
Hi there,

Is there such a thing as a winter thermostat for the 0.8 Cdi engine? I enquired about this at the local Smart centre in Aberdeen, UK. The parts manager could not find anything on his system but confirmed he did not have acccess to parts for Scandinavia and Canada.

I had replaced the thermostat myself on 19 Feb 09. It started failing about three weeks ago. Impossible to get engine temperature above 62 degrees C. I have even blanked off 70% of the front surface of the radiator and engine is still running cold. Visited local Smart centre in Aberdeen and enquired about getting the thermostat replaced under warranty. I was pleasantly surprised when they advised it is guaranteed for 3 years and they will fit a new thermostat free of charge. I had paid nil for the one fitted in February and now I get a new one fitted for free - that is what I call excellent service!
There is a change in the part number for the thermostat fitted to the 0.8 Cdi engine. Part number for the thermostat fitted in Feb 09 is SA6602000315. Part number for new thermostat yet to be fitted is Q0004698V003000000. I suspect there must have been a problem with the existing one since part number has been changed.

Can someone advise part number of thermostat fitted to the Canadian Cdi 450 model?

Cheers,
TK
tolsen
Anyone that knows?
Speedie
As far as I know there is only one thermostat - ties into emission standards and all that. You might want to check for other cooling system problems as well as the thermostat.

I will ask at the local dealership too next time I am by there.

Cheers,
Cameron
tolsen
Thanks Cameron.
TK
tolsen
Have replaced the thermostat.
The reason why engine took ages to get up to operating temperature was because the thermostat did not provide a positive seal. The new thermostat leaks a wee bit as well but not as bad as the old one.

Below photos show the old thermostat being leakage tested:




Heat is lost with the water escaping through the large diameter flow pipe to radiator.

Got a fix engineered on paper. Intend to add an adjuster spindle which will make contact with the stainless steel pin in centre of thermostat element. It will then be possible to adjust the position of the disc such that it will seat and seal properly.

This modification will require some careful drilling and machining. Should be fairly easily done on my lathe.
bilgladstone
Can the thermostat itself be removed from that housing or is it sealed and inaccessible? I'd think if we knew the temperature range and diameter of the 'stat, we might be able to find a quality after-market replacement... ?
tolsen
It is a sealed unit. Not possible to open it out without breaking the housing as far as I can tell. Fitting a valve somewhere between thermostat and radiator is a way around this problem but requires manual intervention to prevent engine overheating. A 12 Volt DC fail open actuated valve would do the job. Could also be a manual 22 mm ball valve with a reach rod operable from driver's seat but that is a bit Heath Robinson.
Speedie
A lot of thermostats have a small hole in them - to let pressure equalize etc. when the engine is heating up or cooling down - they are not designed to be a 100% water tight - so the new one is probably just doing as it ought to.

Cheers,
Cameron
tolsen
The small hole in the disc of a vintage thermostat was there for two reasons:
    [1]To ensure thermostat element is wetted to the coolant.
    [2]To make bleeding easier.
The Smart Cdi thermostat provides a perfect positive seal when a pressure differential is suddenly applied over the disc.

My conclusion is that these thermostats are just poorly made and that the manufacturer failed to correctly assess functional tolerances affecting its sealing capability.

End result: Cdi engines take forever to heat up to operating temperature. This is bad for the birds and the bees and equally bad for drivers and passengers suffering unnecessarily in freezing cold cabins.
tolsen
I have just modified my thermostat to make it adjustable:


The thermostat was centre bored down to the metal pin in the element. Last part of bore hole drilled using a special drill where the tip had been blunted avoiding drilling into the metal pin causing a c0ck up. Bore hole diameter 5 mm. Adjuster spindle made out of marine bronze. Thread size M6. Two O-ring seals fitted on spindle. Tip of spindle drilled out (4 mm diameter) to a depth of 5 mm to centre the metal pin in thermostat element. A4 nyloc nut used as lock nut. Bore hole tapped M6 thread to 18 mm depth.


Assembled thermostat ready for adjustment and testing.


Success. No water leaking out of outlet pipe to radiator. Adjustment was easy. Screwed spindle clockwise until thermostat started leaking, then backed off 1 turn.

Does my Smart heat up faster after this modification?
Answer: I don't know yet, but will soon find out once the thermostat is fitted in the Cdi.
bilgladstone
Great work, man! Any concern that the threads tapped into the plastic bore hole might not hold under pressure?

B sun.gif
tolsen
QUOTE (bilgladstone @ Jan 30 2010 - 09:09 PM) *
Great work, man! Any concern that the threads tapped into the plastic bore hole might not hold under pressure?

B sun.gif

Thread engagement is 17 mm so I am not worried that the spindle will fly out. Axial loading due to pressure is only 2 N (0.2 kg) per 1 bar increase in pressure so next to NIL.
Have just returned from a test drive. Engine heated up really fast and cabin became hot like a dry sauna. While before, the temperature blobs would drop from 3 to 2 when running blower on full blast, now there was no drop at all.

Think I will scan and post the engineering sketch I made of the spindle.
Cheers,
TK
Francesco
If this is an inherent problem, I foresee a small niche market opening up for modified thermostats dispatched from Deeside....
Alex
I fail to see the way the pin works. Are you adding some axial guiding to the valve to hold it centered? You've obviously thought about this, but without looking at the internals of my thermostat I can't see the function of your pin. Not just holding the element closed of course!
4mm ID into a 5mm OD brass pin? Not much wall thickness there, thought about wear?
Nice work, BTW. I do quite a bit of machine work myself, your pin looks lovely.
Keep us informed, every little bit of heat helps in our little ice-boxes.
bilgladstone
Will this affect coolant changes, i.e. will bleeding or "burping" the system be made more difficult in any way?

For your test drive, what was the ambient air temperature, and what length of time would you estimate it took the coolant to reach full operating temperature?

The temperature in my region this winter has ranged fairly consistently between -10C and +5C. I do a lot of shortish runs, not long enough to heat up to 3 "blobs", so fuel economy, engine efficiency and emissions really suffer.

And I echo Francesco's notion that if you are so inclined (or could be persuaded), quite a number of us Canadian smarties might love to purchase a ready-to-install kit from you.

I think you have "hit another home run" with this mod, my friend!

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Pingu
Tolsen - great work to discover the problem and invent a fix. My car has always acted like it has no thermostat. I'm interested to see your sketches. Does the spindle seat the thermostat properly or hold the thermostat closed or both?
Francesco
Yeah, with every front opening blocked -- grille, lower grille, cabin air intake -- I have yet to see three blobs this winter. Interestingly, I did get the ScanGauge to read in the 70s yesterday on a 200 Km run at low-ish revs, despite -18°C temperatures and a very stiff wind. But more often it languishes around 50°.
tolsen
This is Scotland so not as cold as Canada. Only -2 C when I did my test run. I was hoping to get my old thermostat back from MB to cut it open but was told the warranty claim with the supplier might take another month. Spent quite a long time centre drilling through my new thermostat checking nearly each mm depth increment to avoid causing damage. Having done this mod, I am convinced these thermostats are poorly made. The manufacturer got the functional tolerance wrong so they all leak. I am just back from the watering hole and need a rest. Shall post the sketch and other info tomorrow.
robm
QUOTE (tolsen @ Jan 30 2010 - 05:34 PM) *
This is Scotland so not as cold as Canada. Only -2 C when I did my test run. I was hoping to get my old thermostat back from MB to cut it open but was told the warranty claim with the supplier might take another month. Spent quite a long time centre drilling through my new thermostat checking nearly each mm depth increment to avoid causing damage. Having done this mod, I am convinced these thermostats are poorly made. The manufacturer got the functional tolerance wrong so they all leak. I am just back from the watering hole and need a rest. Shall post the sketch and other info tomorrow.


at -20C my cdi is like a freezer unless you drive it real hard (not always possible in bad weather). I am hoping you come up with something!
tolsen
There are lots of additional opportunities of getting engine to warm up faster and getting a cosy cab:


Above photo shows the Cdi engine partly cut through showing internals.
  • Yellow arrow pointing out of thermostat is supply to radiator.
  • Red arrow pointing out of thermostat is supply to heater matrix.
  • Red bendy line out of thermostat is the radiator bypass. Coolant comes out of engine, runs through thermostat housing and is piped back to water pump. I assume there is a restrictor fitted in the black plastic V piece that is bolted on to the water pump.
  • Blue arrow is cooled water from radiator and heater matrix returned to water pump.

Improvements can be made by:
  1. Insulate hoses and expansion bottle.
  2. Rearrange return from heater matrix. The original return is common with radiator which means a large volume of water need be heated. Better to run heater matrix return as separate smaller diameter hose and connect just before V piece at water pump.
tolsen
Coolant being circulated through expansion bottle does really get piping hot. I let my Smart Cdi fast idle at 2000 RPM. Engine was started from cold. Ambient temperature - 2C. Measured +81C in expansion bottle after 10 minutes of fast idle. Here is the proof:

The gauge reads +79.6C. It did read 81C something when I pulled it out of the bottle but I was not quick enough shooting the photo.
This also prooves the modified thermostat functions as intended.
Francesco
Brilliant!
bilgladstone
Super-duper, TK! clapping.gif I SO need to do something like this.

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tolsen
Had my old thermostat returned to me by MB after the warranty claim was completed. Meanwhile I had done some more research and testing. All 3 thermostats I had in my Cdi leaked under low pressure but sealed when I blew or sucked hard i.e. increased the pressure differential over the thermostat element disc. I refitted the old thermostat, then found a way to increase pressure differential and now my Smart heats up to 3 blobs after less than 3 miles of moderate driving. I have concluded that MB c0cked up the cooling system design. Modding the thermostat works but is too complicated and risky. My new remedy is a lot easier but does envolve lowering engine and subframe to gain access. Heater output is fenomenal - so hot that the finger tips get burnt and possible to cook an egg on the heat!
bilgladstone
QUOTE
My new remedy is a lot easier but does envolve lowering engine and subframe to gain access.
Don't keep us in suspense, mate!!!!
tolsen
The solution to sorting out the lack of heat problem is really simple. Just fit a restrictor in the black plastic V- piece that is bolted onto the water pump.

•Yellow arrow pointing out of thermostat is supply to radiator.
•Red arrow pointing out of thermostat is supply to heater matrix.
•Red bendy line out of thermostat is the radiator bypass. Coolant comes out of engine, runs through thermostat housing and is piped back to water pump. There is originally no restrictor fitted in the black plastic V piece that is bolted on to the water pump. Bore size of the two branch pipes of V piece is identical. This is where the restrictor should be fitted on the branch identified by the red bendy line.
•Blue arrow is cooled water from radiator and heater matrix returned to water pump.

Part numbers of black plastic V shaped branch piece:

Roadster 454: 160 200 0156
Smart 450 Merc Engine petrol & diesel: 160 200 0056
Smart 451 diesel: 160 200 0056
Old Smart part number for part 160 200 0056 was Q0003172V002000000. Part number was changed to Mercedes 10 digit number some time ago.

The restrictor increases pressure in thermostat housing and pressure differential over the disc inside the thermostat making the disc seal so no more loss of valuable heat to radiator. Increased pressure means higher flow rate to heater matrix hence higher heat output. Less coolant is bypassing radiator when thermostat is open so more efficient cooling.

Is the 451 Cdi just as bad getting up to operating temperature as the 450 Cdi?

I have ordered a new V piece (Q0003172V002000000) so I can check it out. These are very cheap, only 7 pounds each. Merc parts manager in Aberdeen reckons it is exactly the same part as the old one.


Above photo shows my Mark I prototype version of the restrictor. Mark II version is smaller and incorporates an o-ring. Material is nylon.

Edited part number info. There has been no physical or dimensional changes to that part.
Alex
Nice! What orifice size did you use in the restrictor? And the heater does seem to give enough back-pressure to seat the thermostat properly? Suggestion: Is the other end of the bypass hose any easier to reach, perhaps not needing engine to be moved if you have small nimble hands? It should function the same in any location along the bypass.

(No 451 CDI in North America unfortunately, so I don't think you'll get an answer to that question here. All we get is the non-turbo petrol. So I'm not in the market for a 451, just in case Mercedes are reading this. Hint, hint!)
tolsen
Thanks for replying Alex.

I did consider fitting the restrictor on thermostat side of bypass hose. The problem is how do you hold it in place. The hose is tapered and pressure may push the restrictor through he hose jamming it somewhere or causing damage to pump impellor. I reckon it is a lot safer to let pressure hold it against the barb of the V piece. The o-ring in my mark II version may not be necessary but allows me to machine it on the lathe using a wider dimensional tolerance. The other thing is that I have no control over Mercs dimensional tolerance on the internal bore of the V piece barbed branch.
Bore size is still being tested so not yet cast in stone. I don't think bore size is not that critical as long as sufficient back pressure is created to make thermostat seal.
TK
Francesco
One small concern: how would this affect summer performance? Here in Montreal, summers get quite hot. Crawling along in traffic last year my cdi regularly climbed into the 90s (according to ScanGauge).
tolsen
QUOTE (SameGuy @ Feb 9 2010 - 01:55 AM) *
One small concern: how would this affect summer performance? Here in Montreal, summers get quite hot. Crawling along in traffic last year my cdi regularly climbed into the 90s (according to ScanGauge).

Read post 26 again. "Less coolant is bypassing radiator when thermostat is open so more efficient cooling." I am only fiddling with the radiator bypass. The bypass does not cool the engine. More flow through radiator when termostat is open must mean more efficient cooling.
Running engine at operating temperature will probably make the car more economical.
bilgladstone
Can't wait to have one of these for my car!!! I do loads of short trips and this should bring the engine to operating temperature - and into its best fuel economy mode - much more quickly.

Increased coolant flow to the front radiator in summer and therefor more efficient cooling would be a real bonus!

Adding this to my "Eddy-do" list wink.gif

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Francesco
I have to do my belts and a rad flush soon, so I wonder if I can reach the bypass from the wheelwell....
tolsen
QUOTE (SameGuy @ Feb 9 2010 - 05:18 PM) *
I have to do my belts and a rad flush soon, so I wonder if I can reach the bypass from the wheelwell....

I doubt if you can reach it from wheel arch. There is a good method described by Evilution. He drops the right hand side. As far as I can tell he gets about 8 inches clearance. I have not tried this method myself but it appears to be a lot quicker than using lowering pins. Also no need for ramps and axle stands.
Francesco
That actually does look very straightforward, and it seems to make the belt change a lot easier. Thanks.
Alex
The problem is how do you hold it in place.

Machine a bit of barbs on the OD, size it to the hose ID and put a clamp on. That is IF access is much easier, if you are still lowering the engine then no benefit, of course.
tolsen
QUOTE (Alex @ Feb 9 2010 - 06:42 PM) *
The problem is how do you hold it in place.

Machine a bit of barbs on the OD, size it to the hose ID and put a clamp on. That is IF access is much easier, if you are still lowering the engine then no benefit, of course.

I thought of that as well. The problem is that the hose is bent just before the point where it attaches to the thermostat. It is too easy to loose the restrictor plug deep down in the hose due to its tapered shape.
I have also tried an external device. Here is my Mark 0 restrictor. It fits over the bypass hose and flattens it.


I decided it was too risky as it could short the starter leads that are situated below the hose.
Choking the hose by placing a hose clip anywhere along the hose may work as well but hose may fail prematurely in service. Any work on the thermostat is nearly impossible without lowering the engine a wee bit. Evilutions rhs lowering method looks easy and should be within the capabilities of most DIY mechanics.
Francesco
Confirmed: both part numbers are for the same part. CA$20.50 at MB Canada. Back-ordered in Canada, about a week to get from Stuttgart/Hambach.

I have one on order.
bilgladstone
QUOTE (SameGuy @ Feb 9 2010 - 02:35 PM) *
Confirmed: both part numbers are for the same part. CA$20.50 at MB Canada. Back-ordered in Canada, about a week to get from Stuttgart/Hambach.

I have one on order.

Do you mean the Y-fitting, Francesco? Is that what you have ordered?

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tolsen
The branch piece (V or Y piece) costs 7 GBP (11.9 CAD) here. Mine is coming tomorrow. You are better off holding your horses a day or two. The part is most likely exactly the same as the existing one already fitted in your Smart cars. Owners of the 451 Cdi have reported that the engine is very slow heating up so no better than the 450 Cdi.
Francesco
QUOTE (bilgladstone @ Feb 9 2010 - 05:50 PM) *
Do you mean the Y-fitting, Francesco? Is that what you have ordered?

Bil sun.gif


Yes, that's it.

I figured for $20 it wouldn't hurt to have it in hand, make whatever mod turns out best/easiest, then just swap in the modded part when I do the belts and coolant refill. Then I could forward the used part to someone else who would like to do it the same way. I realize our friend up in Scotland is doing all the heavy lifting here, so I'll be happy to pay forward his kindness that way.
bilgladstone
Let's not get the cart before the horse here... TK is doing more beta-testing yet before the final release. wink.gif
Mike T
Well my new white smart cdi has a fabulous thermostat! The car runs at 84-88 degrees in minus ten weather and even on a steep descent the temperature doesn't get much under 80. Yes, the coolant is full! Heat on demand and it doesn't get over 88 even with the grille completely blocked off by frozen slush, as I found out today. I kept cleaning it out but it would clog /ice up in a few minutes but the temp remained 84-88.
tolsen
Looks like Mike T is one of very few owners that have thermostats that seal. I have tested 3 of these and each leaked to varying degree. The restrictor is a way to work an easy fix to a leaking thermostat.

I collected my new V piece from Mercedes in Aberdeen this morning. Cost me nearly an arm and a leg GBP 7.04 - seven pounds and four pence. It turns out I had misread an email received from the parts manager. Smart has discontinued using the long Q parts numbers and now use the 10 digit Mercedes parts numbers. The V piece part ordered for the new Smart Cdi is exactly the same as my original part. I have corrected part number details in post 26.
tolsen
Can someone post a diagram of the cooling system for the Cdi?
Francesco
I can, but I'm only able to access it after 22:00 UTC ( London time).
bilgladstone
QUOTE (tolsen @ Feb 10 2010 - 06:01 AM) *
Looks like Mike T is one of very few owners that have thermostats that seal.

Ur Mikey has horseshoes up the back of his pants! wink.gif
Duck
WOW @ 80+C in -10C weather. My car is always 60C (two blobs) on long runs at <100 km/h in the winter; only time I see 80C (3 blobs) is if I'm 110-120 km/h sustained. Is it a problem to leave it "the way it is"? Or is it just "over-cooling" the engine?

(@Sameguy - I'd love to see that diagram, as well!)

-Iain
Mike T
Today was even a bigger test...it was minus 23 C across western Minnesota and into North Dakota and the coolant temperature was rock steady at 84-88 degrees when driving at highway speed. Idling would bring the temp down to like 60 after five minutes (I let the car idle for at least 5 after stopping from a hard highway run). Warm air and heated seats, it was more than I expected!
tolsen
Hi there,
I've spent the whole weekend testing various orifice sizes for my restrictor plug. Placed the old Smart on blocks first:

The steamy windows were caused by a wee leakage. Forgot to fit the temperature sensor before topping up coolant.


Above photo shows location of coolant drain plug on the Cdi engine. 6 mm hex.


The rope on the drive shaft ensures coolant runs into my bucket.


Red arrow points to location of V piece bolted onto coolant pump.


A restrictor plugs has been fitted.


Special Hultafors tool very useful when working on hose clamps.


Attached a remote temperature sensor to the hose that runs from thermostat housing to radiator. It is through this hose that valuable heat is lost.

Test program:
Tested 4 different restrictor plugs. Let engine heat up to 59 Centigrade at idle speed. Measured engine temperature in expansion bottle. Read off temperature at hose to radiator. Drained coolant after each test and filled system with tap water, hence same starting temperature during each of the 4 tests. Heater fan was turned off. Tap water temperature 7 Centigrade. Ambient temperature 5 - 9 Centigrade.

Test result:
Prototype restrictor plug. Measured 30 Centigrade in thermostat housing to radiator hose.
Small bore restrictor plug. Measured 14 Centigrade in thermostat housing to radiator hose.
Medium bore restrictor plug. Measured 41 Centigrade in thermostat housing to radiator hose.
Small bore restrictor plug bored out a further 0.5 mm in diameter. Measured 15 Centigrade in thermostat housing to radiator hose.

Went for a 40 km spin with the last restrictor plug tested (the one where bore was increased by 0.5 mm). Fantastic heat output. Up to operating temperature after 6 km. I was worried the plastic dash would melt. The only thing that remains to be verified is whether there is any gain or loss in fuel consumption.
bilgladstone
Outstanding R&D efforts, TK!

How frustrating that the specified fitting is so close yet so far that the engine must be lowered! It looks as though this would be a relatively simple install but for that.

Makes me begin to consider the possibility of cutting in a secondary flush access door for access to that side of the engine...

Bil senile.gif
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