Winter Thermostat For 0.8 Cdi Engine?

[tolsen 630]

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 630]

Anyone that knows?

[Speedie 4]

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 630]

Thanks Cameron.TK

[tolsen 630]

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 13]

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 630]

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.

Edited January 28, 2010 by tolsen

[Speedie 4]

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 630]

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.

Edited January 29, 2010 by tolsen

[tolsen 630]

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.

Edited January 30, 2010 by tolsen

[bilgladstone 13]

Great work, man! Any concern that the threads tapped into the plastic bore hole might not hold under pressure?B

[tolsen 630]

Great work, man! Any concern that the threads tapped into the plastic bore hole might not hold under pressure?B

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 71]

If this is an inherent problem, I foresee a small niche market opening up for modified thermostats dispatched from Deeside....

[Alex 21]

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 13]

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!Bil

[Pingu 0]

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 71]

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 630]

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 1]

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 630]

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:

[*]Insulate hoses and expansion bottle.

[*]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.

Edited February 2, 2010 by tolsen

[tolsen 630]

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.

Edited February 4, 2010 by tolsen

[Francesco 71]

Brilliant!

[bilgladstone 13]

Super-duper, TK! I SO need to do something like this.Bil

[tolsen 630]

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!

Edited February 7, 2010 by tolsen

[bilgladstone 13]

My new remedy is a lot easier but does envolve lowering engine and subframe to gain access.

Don't keep us in suspense, mate!!!!