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VWinVT
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Joined: April 21, 2013
Posts: 1541
Location: North East Kingdom
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 Posted: Wed Jan 22, 2014 5:34 am Post subject: Aircooled Cylinder Head Temp. Sensor |
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| I am planning to install a CHT on my newly rebuilt motor (81 Westy). I have read that it is to be installed on #3 spark plug. I know in the older aircooled motors, #3 was the 'hot spot' and could suffer valve failure. However, I know this issue was remedied with changes in cooling design. So, are CHT sensors still being installed on #3 because old habits die hard, or is there still a reason for the install on #3. |
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Randy in Maine
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Joined: August 03, 2003
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Location: The Beach
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Jeff's Old Volks Home
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Joined: December 19, 2011
Posts: 819
Location: Chester Basin, Nova Scotia
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| Posted: Wed Jan 22, 2014 7:40 am Post subject: |
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#3 cylinder was the hot one in the old air cooled babies because the oil cooler pre-heated the cooling air, as a matter of fact a factory air cooled distributor retards the timing by 3 degrees on the lobe that opens the points to help with that issue.
I've seen lots of 2.0 air cooled vans with the head stripped where the CHT sensor threads in at #3 so I've moved it to #2 and extended the wire. and trimmed the sheet metal a bit to fit.
They run just dandy.
Jeff |
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VWinVT
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Joined: April 21, 2013
Posts: 1541
Location: North East Kingdom
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| Posted: Wed Jan 22, 2014 7:50 am Post subject: |
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| So I guess I want to know is does #3 still run hotter on the 'newer' air-cooled motors? I have read that it is a bit of a pain to install on #3 and if another cylinder is easier to get at, will it provide accurate temperature readings? |
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FNGRUVN
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Joined: October 27, 2007
Posts: 2237
Location: Fort Collins, CO
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| Posted: Wed Jan 22, 2014 8:01 am Post subject: |
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I've always wondered if you could put the sensor on the 1/2 head, where the temp II sensor hole is. It wouldn't get as hot here as the spark plug hole, but aren't we just watching for trends in temps and not so much actual temp?
As mentioned before, go with the Dakota Digital. The VDO gauge is pretty, but not as functional.
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"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." - Benjamin Franklin |
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VWinVT
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Joined: April 21, 2013
Posts: 1541
Location: North East Kingdom
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| Posted: Wed Jan 22, 2014 8:14 am Post subject: |
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| I agree with the Dakota Gauge, that is what I plan to use. Never considered the Temp II port…that would be very easy to access. Has anyone ever used this location? |
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MarkWard
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Joined: February 09, 2005
Posts: 18737
Location: Retired South Florida
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| Posted: Wed Jan 22, 2014 9:01 am Post subject: |
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| On our 68, I installed the temp sensor under a head nut on #3. I ran the wire out a grommet in the sheetmetal. It did not make sense to put the sensor under the spark plug for a few reasons. The head torque on spaghetti studs was around 18 which is similar to a spark plug and there were no issues with the gauges repeatability. |
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Jeff's Old Volks Home
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Joined: December 19, 2011
Posts: 819
Location: Chester Basin, Nova Scotia
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| Posted: Wed Jan 22, 2014 10:23 am Post subject: |
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There is nothing in the cooling system that would add to the temperature of a properly tuned and sealed 2.0 air cooled Vanagon.
Jeff |
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VWinVT
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Joined: April 21, 2013
Posts: 1541
Location: North East Kingdom
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| Posted: Wed Jan 22, 2014 10:58 am Post subject: |
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| rsxsr wrote: |
| On our 68, I installed the temp sensor under a head nut on #3. I ran the wire out a grommet in the sheetmetal. It did not make sense to put the sensor under the spark plug for a few reasons. The head torque on spaghetti studs was around 18 which is similar to a spark plug and there were no issues with the gauges repeatability. |
What issues are you referring to with installing under the spark plug? Using a head nut sounds a lot more straightforward and simple. Were you happy with the accuracy of the gauge under the head nut? |
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MarkWard
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Location: Retired South Florida
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| Posted: Wed Jan 22, 2014 11:08 am Post subject: |
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This was on a type 1 engine, so access to the #3 plug was not the easiest. In those day, spark plugs were changed every 15,000 miles. It seemed it would not hold up to constant torquing of the replacement spark plug and would be in the way when changing the plug.
I can't account for the accuracy of the gauge reading, but on the flat, the temp was very stable. Come to a hill and the temp would increase, coasting down the hill, the temp would decrease.
If I had a 2.0 air cooled engine, I would want to monitor exhaust temp more than head temp. I would also monitor all 4 cylinders. These engines were highly stressed and it did not take much of a change to melt a piston or worse. EGT is a true example of what is actually going on in the combustion of the cylinder. Aluminum melts around 1500 F. |
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Randy in Maine
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| Posted: Wed Jan 22, 2014 11:17 am Post subject: |
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The TSII location is not suitable for determining the CHT. If you intend to use that or some other location, don't even bother with the gauge because it will not provide useful information. No information beats bad information.
Do it as it was intended with the sender under the spark plug and the head modified as German Supply suggests. I leave the sealing washer on the spark plug. |
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Wildthings
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| Posted: Wed Jan 22, 2014 11:54 am Post subject: |
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| On a Vanagon engine #3 is probably the easiest cylinder to install the sensor in as the hole in the tin is not as deep and there is less FI stuff in the way. If you use some other location than under the spark plug you will see different results than you would if you install the sensor under the plug. If you use the location of the FI TSII, the HTS sensor would be heavily affected by the cooling air so the reading might not mean much. If and when you have the engine out and the tin off you can cut the ring off the sensor (leaving the crimp on the end of the wires) and drill a hole in the boss next to the plug and epoxy the crimped into the hole. This way the sensor is close to the plug location but you don't have to mess with it when you change out the plugs. Some have cut a notch in the boss next to the plug to accept the crimp on the ring connector which keeps the ring from spinning as the plug is removed and installed. |
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bluebus86
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| Posted: Wed Jan 22, 2014 1:11 pm Post subject: |
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best to not use the spark plug mounting of the thermocouple. This mounting is popular cause it is easy, however the ring terminal is a difficult fit in the counter bored spark plug hole. and the ring terminal is not as good a sealing washer as the spark plugs crush washer, and the ring terminal can alter the depth of the spark plug into the combustion chamber.
I have mounted them on the head at the base of a cooling fin with drilled hole and thru bolt/nut combo. thus it wont interfere with spark plug replacement.
If you insist on the spark plug location, any of the four will work about the same, but you will want to grind some clearance in the plugs counter bored hole to allow room for the ring terminals crimped end and wire to better clear the spark plug/hole area.
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borninabus 
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Joined: May 18, 2006
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Location: Arizona Highways
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| Posted: Wed Jan 22, 2014 1:17 pm Post subject: |
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my personal experience with CHT sensors is that the ring terminal is a PITA when installed under the plug UNLESS the head has been machined for this purpose.
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Red Fau Veh
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Location: Prescott Az.
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| Posted: Wed Jan 22, 2014 1:29 pm Post subject: |
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Can it be machined in the bus?
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bluebus86
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| Posted: Wed Jan 22, 2014 1:38 pm Post subject: |
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| Red Fau Veh wrote: |
| Can it be machined in the bus? |
difficult at best. You need to get a threaded plug to install in the sparkplug hole flush, to keep debris out, then you need a die grinder with a burr that can reach what you want to remove, all while doing it sight unseen, in a tight spot.
If you could remove the cylinder tin, that will allow better access. I have only done this with motor out, tin removed. I still don't like this mounting location, however it is somewhat acceptable if the counterbored hole is machined out to clear the ring terminal, as I mentioned in prior post.
Without opening the counterbore up to clear the terminal, it is a crappy location, workable, but really crappy.
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Wildthings
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| Posted: Wed Jan 22, 2014 1:59 pm Post subject: |
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| bluebus86 wrote: |
| I still don't like this mounting location, however it is somewhat acceptable if the counterbored hole is machined out to clear the ring terminal, as I mentioned in prior post. |
2x
The method that just drills a hole on the boss next to the plug is easy to do and will read almost the same as having the ring installed under the plug. It does require the removal of the tin and is certainly easier with the engine removed. If the OP head has the boss for the early TSII location then that is easy as well. If the early TSII boss has been drilled and tapped then one can just take an old TSII sensor, knock the guts out, screw the resulting "nut" into place, and then epoxy the thermocouple crimp into the sensor "nut". If the early TSII boss is there but not drilled and tapped, then drilling a hole in the boss just deep enough to accept the thermocouple crimp and epoxying the crimp into the boss is the easiest method of all and can be readily done with the engine in place, but with the tin removed. |
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VWinVT
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Joined: April 21, 2013
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Location: North East Kingdom
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| Posted: Wed Jan 22, 2014 6:23 pm Post subject: |
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| Randy in Maine wrote: |
The TSII location is not suitable for determining the CHT. If you intend to use that or some other location, don't even bother with the gauge because it will not provide useful information. No information beats bad information.
Do it as it was intended with the sender under the spark plug and the head modified as German Supply suggests. I leave the sealing washer on the spark plug. |
I think that I may want to avoid tapping/drilling and such and stick to the 'KISS' philosophy. You mention leaving the sealing washer in place...do you leave it above or below the sender? Does it impact the firing of the cylinder...i.e. spark plug depth?? |
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bluebus86
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| Posted: Wed Jan 22, 2014 6:55 pm Post subject: |
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| VWinVT wrote: |
| Randy in Maine wrote: |
The TSII location is not suitable for determining the CHT. If you intend to use that or some other location, don't even bother with the gauge because it will not provide useful information. No information beats bad information.
Do it as it was intended with the sender under the spark plug and the head modified as German Supply suggests. I leave the sealing washer on the spark plug. |
I think that I may want to avoid tapping/drilling and such and stick to the 'KISS' philosophy. You mention leaving the sealing washer in place...do you leave it above or below the sender? Does it impact the firing of the cylinder...i.e. spark plug depth?? |
yes, the ring terminal effects the spark plug depth into the combustion chamber.
I don't know why the other poster thinks that a location other than the spark plug washer is not worth the bother. you can get good temperature data at many locations on the head, including the stock head temp sendor location, spark plug hole, or a bolted on thermocouple on most areas of the head that are near the combustion chamber.
You really cant do a direct comparison of head temps between gages unless you get them calibrated anyway. Besides that many head temp thermal couples are not compensated, which means outside air temp at the gage will effect reading.
Remember unless compensated, an actual head temp of 380F may read 380F on a 70F day, but it will read 420F on a 30F morning, even though the head is realty at 380F, likewise on a hot day at 100F that same temp of 380F will read at 350F.
with gage variations, wire and connection resistances and such, you cant make comparisons between cars unless things are calibrated, and compensation is used (either built into the gage or by you doing the math considering the ambient temperature).
however do not despair, what the head temp gage is really good for once you get a baseline reading under given conditions, you can then monitor for unusual conditions such as over heating if say you're pushing the van too hard on a hot day, or if the mixture or timing gets screwed up.
Even a gage without numbers is useful in this case, it will alert the driver to conditions outside of the normal operating range.
I just hate the way the ring terminal thermal couples fit around the spark plug hole, makes spark plug change a pain, the wires gets squeezed, or broken between the plug and counterbore, etc... a remote from spark plug location fixes these issues. By grinding a clearance on the side of the counterbore will give you space for the ring terminal, alleviating some of the issues if you insist on the spark plug location, but your still left with the ring terminal under the spark plug
Trust me, mounted on the stock head temp location the gage is a very good tool, and will provide good information to the astute driver. It will not provide bad information.
If you go for the cheaper simple gages that are not compensated (KISS) then it really don't matter, daily air temperature variations (ie weather) can alter the reading by 30 degrees or more.
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Randy in Maine
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| Posted: Thu Jan 23, 2014 8:36 am Post subject: |
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In one of the other threads on this issue over in the baywindow forums, someone reported that there is as much as a 100º difference between the head temperature when measured at the spark plug vs when measured at the TSII location.
That being said, why not just do it as it is supposed to be done? Notch the head as described in the German Supply tech article (I used a dremel tool to do it) and secure the wire to the cooling fins as Scott explains how. I used a grommet to allow a nice spot for the wire to get through the engine tinwork. Done correctly, it will tell you what you want to know and will last for a long time. Do it right and be done with it.
I was initally "pained" to notch those beautiful Len Hoffman heads from my Camper Special when I did mine, but the sender fits smartly in there (sealing washer for the plug is on top of it) and after several spark plug changes there have been no issues. I have the Dakota Digital set up to "flash" when it hits about 400º so that I don't have to watch it all of the time.
While you are in there, replace those spark plug seals with these and use the 5th one for the oil pressure sender "hole". Works really nice if you have an extension to allow the use of a oil pressure gauge. Those spark plug boots are a real loss of cooling air and a tighter fit is a real plus.
http://coolfj40.stores.yahoo.net/tierodbootfj.html |
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