Head Temp Gauges: Do they really work?

Hello all,

I'm retuning my freshly rebuilt V1 today and it has got me thinking. I am asking this question sort of in the perspective as a skeptic, but I want to hear what people have to say.

Now with tuning most engines, I know EGTs tell a great story about how well everything is performing. Realistically speaking (at least not as of yet), EGT readings on a moped can't easily be obtained without a lot of money/time/modification, etc.

So basically what I'm asking is this: what ARE the head temperature readings exactly? Do they REALLY give an indication of the performance/health of an engine like EGTs? Are the "sub ~400*F" measurements arbitrary or are they linked to theory (SCIENCE haha)? And lastly, how can one trust a measuring device that has a bunch of ambient air blowing right by its sensor?

I'm interested in your responses, so gurus: please chime in.

Re: Head Temp Gauges: Do they really work?

Andy Pabstalaniec /

There isn't really a bunch of ambient air, the sensor is clamped between the cylinder head and the plug. There is some ambient air, but it will only cool the sensor about as much as your cylinder head would cool your engine if you cut all the fins off. get it?

I think they're mostly a security blanket, but they can help you when you're tuning. For example, I noticed when I retarded my timing, I ran a whole 30 degrees cooler overall. The temp gauge helped me there. (edited)

Re: Head Temp Gauges: Do they really work?

Christian Giron /

The copper rings are in direct contact with the head and barely touch any of the air since the spark plug covers it

Theoretically speaking,

Because the air is blowing, its a convective heat transfer to the copper ring. This equation is a function of the area exposed to the air. Because there is a spark plug screwed onto the copper ring, it minimizes the amount of area exposed to the air.

On top of this, conduction is typically much more efficient than convection at transffering heat. This is partly why watercooled setups are preffered.

The gauges may not be EXACTLY telling you the correct degrees partly because there isn't perfect contact between the copper ring and head (there are microscopic air pockets in the material that get in the way, this is why we have thermal grease for computer chips, to fill those spaces in to create PERFECT contact), and the thermal conductivity of the head may resist some of the heat transfer form the combustion chamber.... but the gauge gets pretty damn close. (edited)

Re: Head Temp Gauges: Do they really work?

Redundant thread is redundant. 'which gauge should i get' 'why do i need one' 'why does mine suck' 'why did it break'

The 400 measurement has been found to blow up mopeds. Why question it?

The sensor goes Under the spark plug, and its made of metal. Air blowing by the sensor? no

Huh, I got an egt on my moped, and its kinda a $80 sucky pile till I get my tuning fixed up.

zzzzz

Re: Head Temp Gauges: Do they really work?

The trailtech ones are a nice tuning tool. Not a seize prevention tool.

Re: Head Temp Gauges: Do they really work?

CHT is a good way to find out the head temperature once the metal has been heat soaked. EGT is a lot more instantaneous reading of what is working (or not) right now.

Analog self powered ones are the way to go. Also get some bugs for them or pieces of pinstripe tape to mark the temperature data points you want to watch out for, that way you dont have to actually read the gauge, just glance if the needle is pointed where it should be. Also rotate the gauge so that 'normal' is needle pointing straight up.

Re: Head Temp Gauges: Do they really work?

nerdzilla No mo Peds no mo /

I have one on all my bikes. I'm cheap, and I don't want to buy a new kit. It's kit insurance to me. Pull choke ifn it goes over my max temp, and then go figger out what's the issue. Not perfect. Not a panacea. But it works for me. Never siezed or sOftied. Even on my daily with miles of wot 55mPh.

Re: Head Temp Gauges: Do they really work?

I've only seized one time without detonation before hand, it was due to a leaky base gasket. I doubt even a head temp sensor would of helped since the leak wasn't enough to lean the mix out enough to detonate, it was just enough to cause the corner of the piston not to get oil. Also a head temp sensor will read different on every bike even if the temp inside the combustion chamber was to be the same. Also you want the combustion chamber to be as hot as possible to minimize combustion heat(pressure) loss aka maximizing thermal efficiency, it's why new cars run hotter than old ones. So many factors come into play that setting a number for max temp is almost impossible and doing so will only lead you to making less the max power or into detonation and not showing up on the gauge until it's too late. My point being there is one sure fire way to check if too hot(detonating). Hit the kill switch. and it's free!

Re: Head Temp Gauges: Do they really work?

nerdzilla No mo Peds no mo /

Hit the kill when she's hot and you'll sieze fer sure. Pull choke, cool er off a bit.....

Re: Head Temp Gauges: Do they really work?

yeah because cutting the spark, and therefore loss of combustion heat, will somehow make the bike run hotter.... nice logic.

just take my advice. Hit the kill switch while maintaining wot and if it pops loudly from the exhaust your head pipe is too hot and therefore your engine is nearly too hot, or you have an exhaust gasket leak. If it doesn't smoothly decelerate but instead stumbles for a moment and then slows down you're into detonation. If it continues to run until you also close the throttle you're into preignition. This has never let me down and has made it where I can raise the compression to just detonate on 87 and then I'll throw 91 in it. Like a night and day power difference. I bet a lot of people with head temp gauges are detonating and don't even know it. In fact I'd bet on it due to all the people saying they can only to go wot for a short time before their temp spikes<that's detonation showing itself on the slow to react gauge but a little damage is always done in the form of scuffing from the oil being burnt off the cylinder walls. You should be able to blast wot all day long without the temp spiking(detonation), if not you just got an engine that'll slowly eat itself. or don't listen i dont care

Re: Head Temp Gauges: Do they really work?

nerdzilla No mo Peds no mo /

Naw man. If it's hot and you kill it, the piston+ cylinder are hot and expanded, possibly melted into each other becoming stuck. Choke it and cool it, then kill it. That's the logic.

Re: Head Temp Gauges: Do they really work?

I think you accidentally confused what I said with the whole shutting the throttle going down a hill debate and posted before you realized your mistake and are now making shit up so you don't sound stupid. Trying to save face is not an excuse to be a jackass...or maybe you are just that stupid. (edited)

Re: Head Temp Gauges: Do they really work?

nerdzilla No mo Peds no mo /

Um no. Ok. Thanks for being a dick. Have a sweet life bro!

Re: Head Temp Gauges: Do they really work?

campeona del mundo /

ha someone's cranky!

nerdy has a point...if you're running suuuper hot it would probably be a better idea to choke and kill it to prevent any funny business

Re: Head Temp Gauges: Do they really work?

Jonny Appleseed /

So when you kill it at WOT you're looking for smooth deceleration? Anything but that would indicate hot temps/poor running conditions?

Re: Head Temp Gauges: Do they really work?

Choke it!

Re: Head Temp Gauges: Do they really work?

Ryan Mayer Wrote:

-------------------------------------------------------

> yeah because cutting the spark, and therefore loss

> of combustion heat, will somehow make the bike run

> hotter.... nice logic.

Nerdy does not have a point. Read this ^ again. If you cut the spark, non of the gas is igniting and non of the oil is burning, so both work to cool and lubricate the cylinder and piston. If you pull the choke, either that same thing happens because now the mix is too rich to ignite, or it fourstrokes and still adds some heat to the cylinder.

Re: Head Temp Gauges: Do they really work?

finally, someone that uses their brain.

(edited)

Re: Head Temp Gauges: Do they really work?

Thanks for the responses, pretty much right on que with what I was thinking.

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