300tdi Conflicting Thermostat Details

Uys · Jul 17, 2024

Hi, I'm ticking off the usual overheating issues one by one, and will only focus on the thermostat here.

- I tested my current 88deg stamped Thermostat in water and it is only fully open at 97+ deg C (see photos)

- Then tested an out of the box 88deg stamped Circoli thermostat and found the same.

- UPDATE - I now tested my new OEM Waxstat ERR3291G, and .....found the same. Not starting to open until 90 deg C, then fully open around 97 deg C.

The workshop manual has conflicting info. In the repair section (attached) it states that it needs to be OPEN between 85 and 89.

Convention states that the stamped rating of 88 should be the temp the thermostat only starts to open.

The Circoli for example states "Once the temperature of the coolant rises to between 180 and 195 F (82 - 91 C), the thermostat starts to open, allowing fluid to flow through the radiator. By the time the coolant reaches 200 to 218 F (93 - 103 C), the thermostat is open all the way.

QUESTION - Is the manual wrong in the testing procedure, or in the specified thermostat? Do we actually need a lower rated Thermostat like this 78 deg one in the 300tdi?

discool · Jul 17, 2024

The correct thermostat for the 300Tdi is ERR3291 and its stated to be fully open at 88c, so if thats true it will at begin to open 82c or there about.

88c is identical to the 200Tdi thermostat ERR2803.

Uys · Jul 18, 2024

discool said:
The correct thermostat for the 300Tdi is ERR3291 and its stated to be fully open at 88c, so if thats true it will at begin to open 82c or there about.

88c is identical to the 200Tdi thermostat ERR2803.

Thanks. A waxstat ERR3291 one on the way. Will be doing the test on the hob again and report back.

lynall · Jul 18, 2024

I found that all the 88 stats on my 200 did not open until the temp gauge showed 94ish degc them temp rapidly fell to low 80s.
Some did not open at all!

Uys · Jul 18, 2024

lynall said:
I found that all the 88 stats on my 200 did not open until the temp gauge showed 94ish degc them temp rapidly fell to low 80s.
Some did not open at all!

I am starting to suspect a 30 year old misconception and error in the workshop manual!

sierrafery · Jul 18, 2024

Uys said:
Thanks. A waxstat ERR3291 one on the way. Will be doing the test on the hob again and report back.

Hi, IMO if your 300Tdi overheats with the proper ERR3291 thermostat no need to do any tests on that cos the problem is definitey somewhere else

lynall · Jul 18, 2024

Uys said:
I am starting to suspect a 30 year old misconception and error in the workshop manual!

It could also be modern stats are wakn!

I have had a few duff ones in my quest to find one that kept on working.
Waxstat were good, but then for some reason I could not get them for the 200.

Uys · Sep 9, 2024

Uys said:
Thanks. A waxstat ERR3291 one on the way. Will be doing the test on the hob again and report back.

Tested the Waxstat. Same. Not opening until low 90's, fully open around 97 deg C. Would love someone else to confirm this.

Stanleysteamer · Sep 9, 2024

Beginning to wonder if your test with the water static, in a pan, is not a good test.
There would be pressure involved as well when fitted as all car systems operate under pressure so they only boil up when the pressure is released. And the stat would be conducting heat away from itself to its mounting.
Maybe if you mounted each one in turn and then measured the temp in the pipe, or by touching the pipe, just downstream of the stat.

Just saying.

Stanleysteamer · Sep 9, 2024

Here is a method of testing a stat, still using a pan of water, but using it in a different way, provided by a stat manufacturer.

Engine coolant thermostat: Understanting and testing it | Industrias Dolz

There are several ways to check the health and performance of your engine coolant thermostat and you don’t necessarily have to remove it.

www.idolz.com

300tdi Conflicting Thermostat Details

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Engine coolant thermostat: Understanting and testing it | Industrias Dolz

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