Sunday, October 25, 2009

A cheap way to measure your jugs' temperatures?

I figure with this title, I will catch Mr Riepe's attention. : )

But seriously, I was cruising the online forums today seeing how folks measure the heat put out by their boxer engine cylinder heads while the engine is running.

The usual solutions were trotted out:
  • Thermocouple attachments under the spark plugs with wires leading to a meter.
  • Touchless Infrared Thermometers one points at each jug for a realtime measurement.
  • A dipstick with a thermometer at the top.
Prices ranged from not too bad ($40-100) to high (>$200). Those who read this blog, know my tendency to go cheap (usually to my regret later). So of course, I kept looking.

Then, on the site, this guy posted a picture of how he'd just used a plain old meat thermometer and rigged it onto his engine's jug. Simplicity itself!

I rode to the local grocery store, picked up two for $5.00 each. (If I'd paid attention, I could have bought three for the price of two). They come apart easily enough, I discard the aluminum/tin frame that came with them and carefully pried the cover off:

A couple of small holes to match the holes in the metal strap and the leftover screw size

I used lock washers to hopefully keep the screws in place in spite of engine vibration

In case you've ever wondered what causes the needle to move with temperature changes

Mounted, looks good there to me, the metal strap I just bent and curved around the tappet cylinders

So there you have it, a bit of metal strapping, some leftover screws/nuts and it even looks like it belongs there on the jugs! We'll see how long they last with the engine vibrations and such but for now.....

If they work out, I might do the same for my R80 Beemer's jugs.

Update: 26OCT09: The thermometers were apparently poorly placed to register heat from the jugs, their needles did not move the entire commute home tonight. Back to the drawing board.

Update: 16NOV09: This concept is still a bust.


RichardM said...

The head temperature would be higher than the cylinder temperature but it is an interesting idea. BTW, I'm cheap too, supposedly a character trait of airhead owners.

redlegsrides said...

Richard, yeah, the thermocouple under the spark plug is closer to the combustion point but no anchor points there on the jugs....

Canajun said...

While often accused of being an airhead I've never owned one, so please forgive what may be a stupid question. Why do you care what the temperature is? It's not anything you can control while riding - other than by stopping, at which point the temperature will spike because of the stop in cooling air flow.

redlegsrides said...


you're right in that keeping air flow going over the jugs will keep things cooler.....but airheads, of which I now have two, don't like hot weather and stop/go traffic...if your airhead is close to overheating, you stop and turn off the engine rather than risk damage. Having said that, I've never had issues with overheating on the beemer but I installed these on the Ural as the guy who's riding to Siberia right now, on a ural, swears by monitoring engine temp thru a thermometer-equipped dipstick His name is Hubert Kriegel and the riding he's done and is doing, I figure he speaks from experience.

He did this with his GS airhead first, and now in his fifth year of traversing the world with a sidecar, on a Ural. From what I've read in the forums, you really, really, really don't want to overheat a Ural.....this way, I hope to know when I am pushing it too hard, and can back off a bit.

Canajun said...

Thanks for the response. I didn't realize they were so prone to overheating in heavy traffic situations.

I've spent a bit of time on Kriegel's blog - amazing guy, amazing trip.

Jack Riepe said...

Dear Charlie6 (Dom):

Very clever.

Your ingenuity never ceases to amaze me. You should run a Ural survival class. I thnk the meat thermometers look good on this bike, but I go for somethng of more distinction on the "R" bike.

The cooling system on the K75 (liquid,fan) is extremely reliable. Though on hot days, I occasionally hit the horn as it and the fan are on the same circuit. This tells me the fuse id good if haven't heard the fan come on in a while.

Unlike your "R" machines, sitting in stop and go traffic is less of a trial when you hear that fan run.

Fondest regards,
Jack • reep • Toad
Twisted Roads

cpa3485 said...

All this motorcycle jargon is getting to me. Jugs is a new one for me.

redlegsrides said...

Thanks Jack, ingenuity or cheapness? : )

All that todo about the thermometers and I forgot to look even once at them while riding into work this morning....of course, it was 22 degrees so probably overheating the engine was not an issue.

Cpa3485, boxer engine cylinders stick out on the sides of the engine...hence the moniker: jugs. Either that or beemer riders tend to be preoccupied by such things...ask Jack R.

Unknown said...


I think that a little bit of "Jack" is rubbing off on all of us. I hope Natasha's Jugs don't droop too much as they get older

I was thinking of mounting something like this, then I remembered that I have a temperature gauge, sort of. It is an LED readout showing "bars" not actually indicating temperature readouts. It would be nice to know the exact temp

bobskoot: wet coast scootin

redlegsrides said...

bobskoot....yeah, Jack is quite the influence isn't he?

I considered the ones with a digital readout but my old eyes could not read the display at the distances involved once to get old.

cpa3485 said...

I do have some experience with boxer engines having owned older VW's and more currently our Subarus. I always thought that the boxer engines on classic BMW's make them look exactly that, Classic!

Diamond Dave said...

If you bolt any more dials, levers, locks or lights on this thing, its gonna weigh over 1000lbs and you'll have to turbocharge it to reach 30mph

Unknown said...


How about an exhaust temperature gauge, or if you have an oil cooler put a temp sensor in the hose.

bobskoot: wet coast scootin

redlegsrides said...


good suggestions. no oil cooler on this airhead. re exhaust heat sensor...hmmm