Head Temperature Control Knob (manual Temp sensor II)

[Zeen]

With all the discussion about head temps, I'm glad I can finally post about this. There was no boss in the head to mount the Temp Sensor II in, so it was always giving the ECU the message it was cold, causing rich running. So I was looking for a quick hack, and started researching what the TSII does. From Ratwell's site, it was apparent it was a fairly simplistic input

So I hit upon the idea of using a potentiometer to spoof the ECU into thinking whatever I wanted it to think. A little more research, and found that Dingo had already tried this with success.
http://www.thesamba.com/vw/forum/viewtopic.php?t=111400&highlight=potentiometer

I've been using it basically as a manual choke, turn it to cold (2500 ohms) for start-up, and warm (50 ohms) when I start rolling.

After looking at Richard's graph, I thought there was potential to use it to help control head temps by fine tuning the mixture on the road; basically fooling the ECU into thinking it was cold, and forcing it to richen the mixture. After finally getting my DD gauge installed, and a good road trip to test it, I have some experience to share.

To my amazement, my wife suggested we take the Westy and go camping in the Upper Peninsula as part of transporting our daughter to a camp at Michigan Tech. 1800 miles of everything from Interstate to serious off-road, with a heavy load of 3 people and way too much crap and camping supplies.

On flat ground with no wind, and the knob in the "warm" position, I could maintain 60mph, sometimes 65, with head temps staying around 380F. Add a hill, or a headwind, and they would easily climb above 400F. I found that if I turned the knob towards "cold", I could quickly bring the temps down by 30F and keep them down, even on a sustained hill climb.

I got into the habit of richening the mixture just before I started up a hill, and leaning it out after the crest. If I looked down and saw a temp of 345, I knew I had forgotten to lean it back out after the hill.

The wife was a great sport, but by the 6th day she was done and wanted to get home, so we did the final 580 miles in one day. Once we crossed the bridge she was getting impatient, so I cranked the knob to rich and flogged that poor Westy at 70mph for three straight hours. Not recommended, gas mileage plummetted to 10.5mpg, but it seemed like the right thing to do at the time, and the head temp never once exceeded 390F.

Everyone needs to have a DD CHT gauge. Add this modification, and you can take the edge off your temps on those occasions when you just can't slow down enough to bring them down.
_________________
The consequences of your decisions should not be confused with fate.

[old DKP driver]

I think what you have done is great! this is something that has not been thought about since the old d-jet systems on early 914s congrats..
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V.W.owner since 1967

[jasonious]

I need to do this! Could you post pictures and a schematic? Where did you get the potentiometer with the proper ohms?

Thanks!
Jason

[Zeen]

I'm traveling now, so I can't post pictures, but it's very easy. The Temp Sensor II has one wire coming out of it, which connects to a wire going to the ECU. The Sensor itself is grounded in the head, which forms the complete circuit. So to mimic it, you connect one side of your potentiometer to the wire leading to the ECU, and the other side to a ground; I used the one on the firewall on the left side of the engine. You then just snake the wire up to the dashboard, following the bundle of wires that go through the grommet on the left side. I got the potentiometer at Radio Shack. I was hoping to find a 0-5000 ohm model, but they only had 0-10,000 which works fine. There was an unused bracket under the dash that fit perfectly, so I installed the pot there, and used an ohmmeter to mark where 50 ohms and 2500 ohms fell.
_________________
The consequences of your decisions should not be confused with fate.

[Randy in Maine]

I don't know if you can access this forum or not http://forums.aircooledtechnology.com/showthread.php?t=1195

but Ray Greenwood has some additional information on how to do it.

[musktchup]

Very nice, with some fiddling you could possibly get better mileage.

[IFBwax]

Don't you run the risk of running too rich though and hurting something?

Just asking... I don't know the answer.
_________________
Owner of: "The Party Pickle" (a 1979 2 Liter FI "Raby Camper Special" Sage Green Westy Campmobile) & "Charlie Brown" (a 1979 2 Liter FI "Rob Grant Rebuild" Agate Brown/Dakota Beige Station Wagon)


www.partypickle.blogspot.com

[aggri1]

Running rich will wear out piston rings faster and you'll need more regular oil changes won't you?

Intersting idea, but I'd be concerned about running rich for extended periods of time.

Cheers, a.

[Zeen]

[JMazier]

[Zeen]

[johnlynch47]

I found 2 Potentiometers at radio shack, both 0-5k ohms 1 is 500vdc 0.5w and the other is 250vdc 0.25w which one should I use?
_________________
"My shovel is sharp, my pick is sharp, and my will is outstanding." - Rod Marinelli

"I've got a good heart, but this heart can get ugly" Rapper DMX

"Bring your face over here so I can smack it" My Mom

1977 Sage Green Westy up in this!
her name is Velma
1994 Chevy Silverado - Mater
2006 Kia Sedona - Pearl

[telford dorr]

Whichever mounts up the best. Voltage and power rating is not a factor in this application.

I ran this exact same setup on my '71 bus with '75 bug FI. Worked great until the FI harness got too brittle and became a reliability issue...
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[Wildthings]

[johnlynch47]

So I have made my switch (very temporary) does it matter what wire is hooked up to what side? Im guessing not as it is just completing a circuit. I will have it set up so it will be very easy to switch. Cross your fingers

_________________
"My shovel is sharp, my pick is sharp, and my will is outstanding." - Rod Marinelli

"I've got a good heart, but this heart can get ugly" Rapper DMX

"Bring your face over here so I can smack it" My Mom

1977 Sage Green Westy up in this!
her name is Velma
1994 Chevy Silverado - Mater
2006 Kia Sedona - Pearl

[raygreenwood]

Yes, I did this a couple of different ways a few years back. When my 412 gets back on the road (christmas maybe)....i will have a new version that i finished to run with.

Im not sure how well this will work with L-jet...my version I mean....but it works well with D-jet.

With D-jet....on average the CHT unless its really cold...tends to hover stone cold at about 2500-2900 ohms. In the winter it tends to drop down to about 125-200 ohms fully warm from its max ohms. In the summer with 80+ degree ambient when you wake up in the morning (Texas and Oklahoma)....its about 2300 ohms and will drop to about 100 if everything is running sweet. However....when the ambient is 95+ and especially in city stop and go....you can drop all the way to the lower limit of about 70 ohms.
Typically depending on your baseline fuel mixture, state of tune etc....this can be a bit too lean. Il ike to keep it at 100-125 ohms.

What I found with D-jet is that the wide range from 2300-2500 ohms down to 70 ohms is really not needed.

For instance..yes the 2500= ohms is necessary for cold start up. However with a potentiometer (actually a ceramet variable resistor) in place...i found that the system really reacts almost not at all...change wise...to say...2400 and 2300 ohms coming down from 2500. It makes its first big reaction to about 2100 ohms (at least on the system i tuned this to. each system will be slightly different).

So...2500 and 2100 were definate bench mark points for my system. About 1850 was my next point....then nothing until about 1250.....then nothing until about 900 ohms. Then it got sensitive again at about 650 and was noticably sensitive in about 125-150 ohm increments....and i stopped it at 150.

Thats 10 points. I found that with normal start up and driving the time distance between each point was fairly equal (in this set up for warm weather). You can fairly well run it at about 1 point of step down every minute and a quarter.
I made a small breadboard with soldered on resistors that worked well. i tried it with a bi-metal coil from several sources...it was not very good. Ideally I could use a set up from some AAR....difficult to keep accurate for the long haul.
I had abuddy at work build me a small electronic timer circuit box that would switch from resistor to resistor without breaking ground connection. Thats the one I will be playing with. He is still working out the timer circuit that will shift it back up two points each 15 minutes of stoppage....which is about right I have found.

For winter driving......60f and below....a totally differnt board plugs in. I could use the same one.....but I found for cool and cold weather. I only need 5-7 points and it really only need drop to about 250.

If the elctronic timer does not work out its no problem. I will use a hard wired resistor board with a knob installed at the indention on teh right in my 412 dash. I will print marks on the temp gauge face and simply adjust manually. I kind of like a manual car that makes you pay attention.

I already have a manual lever with a warning light and buzzer that keeps my flaps closed until warmed up. It runs by time...about 6 minutes. It uses a thermistor and a ground on both heads and a ground loop on the flap rod lever. If the heads are already 200F or above...the light and buzzer sounds if I have closed flaps ...say at a 7-11 while getting a beer and lottery tickets.....it was something I cooked up last year when thermostats were getting stupid scarce. Ill let you know how it works out.

The manual CHT works very well. Very smooth warm up. I tried the first version with the ceramet resistor before I toasted my last engine (oil pump issue not CHT).

Good work!

Ray

[johnlynch47]

HOLY CRAP IT WORKED!!! sort of, the bus went from not starting up at all (pre bypass) to now starting up and staying running. however i am on the plus side of 2500ohms the whole time. if i turn it much lower it starts running rough. i need to go back and readjust throttle and what not but at least i can drive it to a shop at least
_________________
"My shovel is sharp, my pick is sharp, and my will is outstanding." - Rod Marinelli

"I've got a good heart, but this heart can get ugly" Rapper DMX

"Bring your face over here so I can smack it" My Mom

1977 Sage Green Westy up in this!
her name is Velma
1994 Chevy Silverado - Mater
2006 Kia Sedona - Pearl

[raygreenwood]

That is indicative (in general) of an overall lean condition. Check your fuel pressure. Also check that you have no constant vacuum leaks...hoses...gaskets...runner tube boots...oil breather...AAR...TB gasket.....injector seals...valve covers etc. Ray

[Paul Hoegemeyer]

If you have a working tsll could you not run two wires to the dash and put the pot in series with it and keep it at zero then when you need to richen the mixture add resistance?
_________________
1978 passenger bus FI. camper special engine
1986 Brazilian DC
1979 Westy waiting on a TDI
1970 beetle

[Wildthings]