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Thermostats that last??

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Where can I buy a thermostat for my 200tdi that lasts more than a few weeks before it starts to under read? I have a VDO temp gauge that reads in degrees and the running temp is currently sat at 80C today. It has been consistently at about 85C  for the last 9-12 months and I lived with that, but the stat only did what it was meant to do and kept the engine at 88C for about a fortnight after fitting. Can anyone recommend one that will work for a reasonable time after fitting? I have had this with about three in a row now. 

The temp gauge is reading correctly - verified by taking the temp at the thermostat housing with an IR temp/imager - the temp on that matches the temp on the gauge.

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I would more likely suspect bad wiring than the thermostat.  

I use a Stant 45779.

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Also how accurate is the gauge and sender?

From https://www.vdo-gauges.com/media/instructions/TU00-0770-5104620 Temperature Sensors_short_version.pdf

At 85C some of their senders have a +/- accuracy of 8.91 %

And as they actually measure resistance then the wiring resistance which can be affected by various things like temperature of the wiring and other factors

While expensive fluke IR temperature guns tend to have an accuracy of +/- 1C
But cheaper ones are known to be +/- 2C
And they also they are measuring from an area (cone) which might include colder components depending on distance measure.
And to add to their inaccuracies the temperature on the inside of the thermostat housing will be higher than the outside.

So overall I think you quest for this level of precision is flawed unless you do measurements in a more accurate setting outside of the car with calibrated instruments and measuring the opening and closing movement of the thermostat vs temperature.

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Never had a problem with Allmakes stats 88 degree one in my engine now, 

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1 hour ago, zardos said:

Also how accurate is the gauge and sender?

From https://www.vdo-gauges.com/media/instructions/TU00-0770-5104620 Temperature Sensors_short_version.pdf

At 85C some of their senders have a +/- accuracy of 8.91 %

And as they actually measure resistance then the wiring resistance which can be affected by various things like temperature of the wiring and other factors

While expensive fluke IR temperature guns tend to have an accuracy of +/- 1C
But cheaper ones are known to be +/- 2C
And they also they are measuring from an area (cone) which might include colder components depending on distance measure.
And to add to their inaccuracies the temperature on the inside of the thermostat housing will be higher than the outside.

So overall I think you quest for this level of precision is flawed unless you do measurements in a more accurate setting outside of the car with calibrated instruments and measuring the opening and closing movement of the thermostat vs temperature.

Hmm. I know what you mean, but isn't it a coincidence that the IR cameta/thermometer matches the gauge exactly? 

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Have your put your thermostat in some hot water and slowly bring the temperature up measuring with you IR gauge and observe what the thermostat actually does?

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No. Not yet Phil. I dont have a spare gasket but I will try it. 

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I’ve never had a problem with genuine ones, which are made by Waxstat I believe. 

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20 minutes ago, Retroanaconda said:

I’ve never had a problem with genuine ones, which are made by Waxstat I believe. 

I fitted a waxstat one from Allmakes to a friends 90 after high trying a load of different ones which didn’t work. 

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The last one came from Turners so I assumed it would have been ok - I will give a genuine one a try.

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Some years back I went through a similiar hunt for consistent stat behaviour. I had examples from our revered purveyor of blue boxes, genuine LR from a stealer, Waxstat, Allmakes, and local factor's cheapy brand. 

I never expected to see so much variance, or that the genuine LR item would be one of the furthest from correct temperature. I think I stuck with the Waxstat one in the end.

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19 minutes ago, mickeyw said:

revered purveyor of blue boxes

:lol: 

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Shop4autoparts sell wax stat ones , brought a few myself .

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I've had trouble with both Waxstat and genuine. It's a lucky dip ! I'm back on the original genuine thermostat that I put in when I built the 90.

The genuine replacement gave a nice 100°c running temperature 😂

Mo

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As Retro says, I buy my stats direct from LR seem to last a couple of years then they seem to go off a bit, I went through buying all sorts, and even some genuine stuff through a 3rd party I was finding was NOS (new old stock) not really any help with stuff with a shelf life.

I've got a madman Engine monitor, using VDO senders, cruising I get 90 deg, if its gentle traffic driving in some of this cold weather with the hater on I can see it dip to 70 deg before it pops back up to 80 something.

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I replaced the unknown one on my V8 with a Gates one. Gates stuff is usually really good, but three months on she now takes ages to warm up if moving and the temp hunts.

I've just bought genuine which is marked as Waxstat. I'll change shortly and report back. 

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Hi, I found that fitting a new stat if the coolent was of an unknown origin or how long it has been in and ratio of anti to water (they say distilled water is also better) that it can also affect the temp readings. If it's not over heating does it matter?

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I dont know how much 80C as opposed to 88C really matters - it isnt overheating like you say, but is everything working at optimum if its running nearly 10C below where it is meant to be?

I have a genuine stat now that i will pop in when i remove the stat housing to replace the stat housing to head seal. I will report back then too.

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When you bear in mind that the original temp for the V8 was 82 until the latter years when it was raised to 88. Similarly there was always a 74 option for series engines as opposed to the normal 82.

Apparently it is easier to reduce the emissions on an engine with a higher operating temperature, or should I say "allegedly"  

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