Problem solved.
New Tstat removed;
Old Tstat re-installed;
(coolant temp gauge needle stays middle of the LED; ECU readout 0.15 V;
thermoscan of coolant pipe around 85C)

On Fri, Jun 26, 2020 at 1:05 AM Gabriel Hourtouat <ghourtouat@gmail.com>
wrote:

> Mark, Dennis,
> -Thanks for your comments.
> -Got some data!
> -comments and guidance?
>
> I think my thermostat wants to keep the engine temp at whatever
> temperature corresponds to 0.12V on the temp sender!
> Tomorrow I will change the Tstat using Dennis procedure form 2018.
> (pasted below the data for reference)
>
> Didn't scan the rubber hoses on this go around; but monitored two temps:
> -"Coolant Temp" signal (using the Shoebox Electronix Monitor, a gadget
> which outputs the signals seen by the ECU to an LCD screen)
> -un-calibrated junky thermo scanner aimed carefully at the same range,
> same spot on steel pipe (scanner resting against the wires in that area,
> about 1 inch off the pipe)
>
> ECU / Pipe / state
> 0.43 / 56C / just started engine
> 0.21 / 75
> 0.18 / 86
> 0.16 / 91
> 0.14 / 94 / rad reads 34C
> 0.13 / 96 / needle on the dashboard is middle of LED
> 0.13 / 97 / needle at top of LED
> 0.13 / 99 / needle above LED
> 0.12 / 98 / needle stable
> 0.12 / 100 / rad reads 50
> 0.12 / 100 / rad 73
> 0.12 / 99 / rad 85
> 0.12 / 100 / rad 86, fan is ON
> 0.12 / 98 / rad 84 fan is still ON
> 0.12 / 98 / rad 83, fan is OFF
> 0.12 / 101 / rad 83, fan ON
> 0.12 / 100 / rad 82, fan OFF
>
> Driving:
> ECU stays at 0.12 at all speeds with little variation
> -bumps to 0.13 when the heater goes to full blast, 0.11 when getting off
> the highway;
> -In all cases, the readout soon gets controlled back to 0.12.
>
> Shoebox Electronix instructions gives some specifications for the coolant
> temp:
> above 0.95V when cold
> 0.17 at Warm idle
> 0.18 at 30 mph
> 0.21 at 60 mph
>
>
> changing the Tstat procedure:
> Do this with engine cold. With system tight you should lose only a small
> amount of coolant removing the t-stat cover. After you put it back
> together open the bypass valve on the cover, start the engine, remove the
> pressure cap, hold engine at 2,000 rpm and top off pressure tank. Replace
> pressure cap, let engine return to idle and you should be good to go. If
> the system is working properly it will finish any other air purging on its
> own.
>
> Dennis
>
>
>
> On Thu, Jun 25, 2020 at 10:48 PM vw_van_fan_Mark <madvws@cox.net> wrote:
>
>> If the coolant returning to the waterpump is really 225F then the
>> radiator fan should be running constantly since that is above the rad
>> fan temp switch shut-off temp. If the thermostat is working then the
>> radiator itself should measure hotter than the coolant returning to the
>> water pump.
>>
>> So I would question whether the thermostat is fully working.
>> If bypass disc isn't closing off the bypass path then some coolant would
>> be able to skip the radiator and just keep recirculating back to the
>> pump. Some coolant would still go to the radiator if the main thermostat
>> disc was opening.
>>
>> If you can measure the temp of the large rubber hose to the top of the
>> thermostat housing and compare it to the temp of the large rubber hose
>> connecting the lower housing to the waterpump feed pipe the results
>> should help determine what is happening. Measure the rubber in both cases.
>>
>> Mark
>>
>> Gabriel Hourtouat wrote:
>> > Celebrations cut short.  Violins start to play...
>> >
>> > Is it possible I have a bad Tstat?
>> > -any opinions and suggestions are MOST welcome...
>> >
>> > after more extensive driving around, engine temp is controlled well
>> above
>> > what I am used to (IE (bottom 1/3 of the LED)...
>> > -temperature gauge:  centreline of the needle is about 1 full LED
>> > diameter above the centre of the LED
>> > -temperature scanner reads 225F on the return pipe to the water pump
>> >
>> > At idle, the coolant fan comes on and controls the temperature at this
>> > elevated temperature.
>> >
>> >
>>
>