Date: Sat, 4 Jun 2011 10:56:46 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Thermostats [Was: Spooked!]
In-Reply-To: <1307195601.18233.857.camel@TheJackUbuntuNetbook>
Content-Type: text/plain; charset="UTF-8"
While a tight fit the thermostat even on the 1.9 engine can be done without too much grief unless the bolts are rusted and/or you snap them. 1/4' drive ratchets, some extensions one with a wobble end and a quality 10mm socket will do it. You will lose maybe a gallon of coolant. Just remove those two screws on the thermostat cover and work it out. You can even leave that hose connected to it.
Having the lower temp thermostat has a number of disadvantages. One no one thinks about is that in hot weather as the cooling system is stressed it gives more room for temperature changes. It may now be normal to go from 80C to 110 or even 120C instead of stabilizing near 87C. This creates additional thermal expansion-contraction cycles for the engine. It is better to let it get hot and stay hot.
The T-stat is not just an open-close operation. It is a mixing valve. On the water boxer its operation and response curve is critical. Particularly in cold weather. I am still buying them from VW due to many disappointments with aftermarket.
If bleeding take more than 3 minutes you have done it wrong and need to wait and try again. The trick is to be done before the engine warms up.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Rocket J Squirrel
Sent: Saturday, June 04, 2011 9:53 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Thermostats [Was: Spooked!]
Thanks for the deeper explanation of how the system works.
I understood that the thermostat isn't a binary on-off thingy, but a device that gradually opens once we hit the bottom end of its range.
Scott said he didn't like the low-temp ones in winter, and what I was questioning was whether that made any especial difference, since regardless of whether it's cold or hot outside, the engine will get hotter and hotter until it reaches the bottom end of the t-stat's range and the t-stat will then work to keep the engine within its control range.
IOW, season does not make a difference?
PS. Thing I've learned is to not disregard Scott's words, but I do like to look at them more deeply.
PPS. I think the arguments here in favor of the stock t-stat are good ones, and if changing the t-stat was super easy I'd do it in a heartbeat. But I somehow sense that we're talking a lot of coolant loss in the process, and a messy driveway, and buckets of coolant to somehow dispose of. Not to mention the whole gosh-darn cooling system filling and bleeding rigamarole.
On Sat, 2011-06-04 at 01:36 -0400, David Beierl wrote:
> At 12:47 AM 6/4/2011, Rocket J Squirrel wrote:
> >Winter or summer, the thermostat will pretty much bring the engine up
> >to 80C (or 87C, depending its setpoint), yes?
> >
> >Seems to me that regardless of whether there is snow on the ground or
> >molten asphalt, the engine will just get hotter and hotter until the
> >thermostat cracks open, and it's the thermostat's job to modulate the
> >amount of water going to the rad to keep the coolant -- at the point
> >where the thermostat senses it -- at the setpoint temperature.
>
> It isn't a setpoint so much as a balance - the 'stat opens over a
> range of about 35F, so while you're in the control range of the system
> the temperature at the thermostat will be between ~185F and 220F. The
> fan will be running at high speed ~ten degrees before the thermostat
> is fully open.
>
> Once you hit 220F you're now dependent on the ability of the
> radiator/fan to reject heat so you've got a new balance between 220F
> and the system boiling point, which should be close to 260F if you're
> running 50/50 ethylene-glycol coolant and your pressure cap is in good
> shape (265F at 15 psi, I think our caps are 13 psi). It's still a
> balance because heat transfer goes up with the square of temperature
> difference.*
>
> Somewhere at the top of that range you'll notice a little red light
> blinking on your temp gauge, and VW specifically says (owners manual,
> page 37 in the '89 book) that elevated gauge temps are "not serious"
> until the light starts blinking. According to "some antifreeze mfr"
> 260F is a common setpoint for engine overheat alarms.
>
> *this margin between 220F and boiling point decreases at altitude,
> since it's absolute pressure and not gauge pressure that really matters...
>
> "Open-deck" engines like the Subaru (according to the Subaruvanagon
> list folks) are not so tolerant of temperature excursions, so the
> Subaru cooling system is regulated a good deal more tightly than the
> WBX in normal operation. It still has the same margins at the
> extremes, but the thermostat system works more crisply.
>
> Yrs,
> d
>
