NFB

Why does the thermostat fail? For the 450 model

20 posts in this topic

Hi Guys

Just wondering why the thermostat part is so expensive? As I recall it is just a bimetal spring that responds to water temperature. Is there a mod for it besides choking the water flow? I'm guessing once opened it can't be reglued unless its ABS material

MotoRad2.jpg

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Our original Smart thermostat is not expensive compared to other cars and to after market thermostats. 

Thermostat element is not replaceable as not possible to open out thermostat housing except on the poorly made after market Gates thermostat seen in photo in post #1. On the original Smart thermostat made by Wahler, the two parts that make up thermostat housing are bonded together by ultrasonic welding. 

Thermostat element fails just like any other thermostat element. Additionally, because element sits on its side turned 90 degrees, the crude internal check valve starts leaking causing engine to take longer time getting up to operating temperature. 

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Do you mean this? 

Quote

the crude internal check valve starts leaking

ThermostatDiscCV.jpg

Edited by NFB

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2 hours ago, NFB said:

Do you mean this? 

ThermostatDiscCV.jpg

Yes that is ours. The crude check valve will hang with its head down just like seen in photo. The wee trickle of hot water leaking to radiator through a non sealing check valve is enough to slow down engine getting up to operating temperature. 

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There are China made copy thermostats fitting the Smart 450 where the check valve is fitted wrong way. These will therefore never seal and always leak valuable heat to radiator. 

 

Purpose of check valve is to ease bleeding of air. 

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This is really bad design. Check valve would have worked perfectly had the disc been sitting horizontally. For vertically orientated disc, a check valve made out of a material having same density as coolant would possibly have worked. Better in my humble opinion if there were no check valve at all. Filling of cooling system would then require vacuum bleeding which now is very common anyway. 

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MotoRad2.jpg

The image shows the Gates thermostat I modified about five years ago. It worked perfectly until last winter when the two housing parts split causing loss of coolant and engine overheating. The two parts are held together with only three small dogs. I intend to sort it one fine day by fitting external C clamps.

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Where does the check valve plate appear in this photo? Is this from an earlier 450 model?

What was the modification you did to improve its performance, did you stretch the spring to slow down the opening rate?

From this picture it looks like the thermostat would unscrew from the housing. Perhaps a chemical adhesive with precision SS screws would have secured it indefinitely after the mod?

 

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Original Gates thermostat has a crude stamped out disc with even cruder check valve. The one I modified has disc turned out of marine bronze with o-ring seal and no check valve. 

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54 minutes ago, tolsen said:

Original Gates thermostat has a crude stamped out disc with even cruder check valve. The one I modified has disc turned out of marine bronze with o-ring seal and no check valve. 

 

It has been a number of years and without re-reading the entire thread on the topic, am I correct in remembering that you did some keyhole surgery in a thermostat and epoxied the check valve in place?

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3 hours ago, smartdriver said:

 

It has been a number of years and without re-reading the entire thread on the topic, am I correct in remembering that you did some keyhole surgery in a thermostat and epoxied the check valve in place?

I tried two remedies on the original Wahler thernostat:

1) Fitted a small o-ring over discharge side of check valve.  The purpose was to get the brass head to move nearer to the hole hoping this would make it seal.

2) Epoxy glued check valve to disc.

 

Both remedies worked but were equally tricky to do.  My present thermostat has the o-ring fitted.

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I also made an adjustable thermostat. I bored out a Wahler and fitted a bronze spindle allowing adjustment of disc height relative to seat. Therefore possible to adjust opening temperature of thermostat. 

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Mr. Tilden Can you please tell me the MB part number for a 2005 or 2006 thermostat? You mentioned it wasn't  that expensive compared to others. Or even a aftermarket one that has shown to be dependable.

Thank you in advance and for the other readers of similar interest.

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Searching by Smart or Mercedes part number does not guarantee you won’t get a fake Gates or worse thermostat. Same if you search with Wahler part number 3146.90D. 

It seems fake parts manufacturers like Gates cross reference their substandard parts with the good original parts. 

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1 hour ago, tolsen said:

Searching by Smart or Mercedes part number does not guarantee you won’t get a fake Gates or worse thermostat. Same if you search with Wahler part number 3146.90D. 

It seems fake parts manufacturers like Gates cross reference their substandard parts with the good original parts. 

Thanks Mr. Tolsen.

How would l know if it's working before installing? I read something about leak testing it but l wasn't  clear on the method. Regards Richie

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I’ve told you before. You suck and blow on the largest hose barb to test if check valve seals. Check valve should seal when sucking.  

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we dont have much choice here for parts 

 

overseas shipping is ridiculous prices

Edited by LooseLugNuts

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