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Mon Feb 01, 2010 9:15 pm

I've read a few postings on CHT temps and it sounds like there are differences in readings depending upon how they're mounted. Mine is a DD mounted on the #3 plug. The temp looks reasonable when I get in in the morning but when I get going it is HIGH! Like 450 on the freeway at 60mph when the air temp is 60 degrees outside. I rises a bit when going a little up hill and down when going down hill. I can't imagine this is good at all!

My question is, what are contributing factors to an engine running hot? Then engine seal is good and tight and *I think* I have all the tin though there are some spots rusted through. I also don't have the little cover over the alternator bolt. Is this enough to cause it to heat-up so much?

Thanks, don

Mon Feb 01, 2010 9:23 pm

first thing you need to do it shoot an infared gun at it near the plug sender and see if it agrees with the DD gauge. If it does then, lack of ariflow, timing or lean mixture can contribute.

Mon Feb 01, 2010 9:41 pm

Quote: I rises a bit when going a little up hill and down when going down hill

I love my VDO CHT Guage. It leaves me worry free. When I start up my bus, after a while my gauge reads 300. If I go up a big hill temp rises to 305, down a hill it falls to 295. It's just so comforting!

Mon Feb 01, 2010 9:50 pm

raymino wrote: I love my VDO CHT Guage. It leaves me worry free. When I start up my bus, after a while my gauge reads 300. If I go up a big hill temp rises to 305, down a hill it falls to 295. It's just so comforting!

Agreed - probably my favorite mod (except for sound proofing the bus) - I just wish it read 300 and not 400!

I don't have an infrared gun but I do have a temp sensor on my VOM that I'll try to use... Incredible that timing/mixture could cause this big a difference!

Mon Feb 01, 2010 10:00 pm

Quote: Incredible that timing/mixture could cause this big a difference!

I wish I knew. Changes in timing have no effect on gauge readings. 295-305. I hear the DD is better than the VDO, but I agree to test it with an infrared gun, if there was one around.

Mon Feb 01, 2010 11:07 pm

How is the sender mounted?

I had a bus that I had used the washer around the plug 3. When I was tightening it on, the washer broke and it caused a much higher reading because of gasses that were escaping.. I ended up gluing it to the block between the fins next to #3. Also remember to remove the crush washer if you're going to use the plug ring.

Another time I had a reading really high and it ended up that the wrong sender had been used to hook it up. I replaced it with one from Dakota Digital (where the gauge was from) and it fixed the problem.

I do agree with above. Get a reading on the temperature at plug 3. It is entirely possible it's the engine.

Hope that helps.

Casey

Tue Feb 02, 2010 10:16 am

Casey Ryan wrote: How is the sender mounted?

I had a bus that I had used the washer around the plug 3. When I was tightening it on, the washer broke and it caused a much higher reading because of gasses that were escaping.. I ended up gluing it to the block between the fins next to #3. Also remember to remove the crush washer if you're going to use the plug ring.

Another time I had a reading really high and it ended up that the wrong sender had been used to hook it up. I replaced it with one from Dakota Digital (where the gauge was from) and it fixed the problem.

I do agree with above. Get a reading on the temperature at plug 3. It is entirely possible it's the engine.

Hope that helps.

Casey

Helps a lot! I have a infrared gun on order so I'll see if the temp is accurate.

I removed the crush ring from the plug and used the DD sensor around the plug. I've not removed the plug since installed but I guess it is possible that it is damaged. I'll get back to y'all when I get a temp reading.

Wed Feb 03, 2010 9:31 am

"When I start up my bus, after a while my gauge reads 300. If I go up a big hill temp rises to 305, down a hill it falls to 295."

I'd bet a dollar that something is not right with your set-up.

The difference in temperature between going up a big hill and down a big hill should be much more than 10°. CHTs go up and down very quickly.

305° is also VERY cool for climbing a big hill.

It might be comforting, but I'm pretty sure you're not getting the whole story.

Wed Feb 03, 2010 9:50 am

Patrick199 wrote: The difference in temperature between going up a big hill and down a big hill should be much more than 10°.

i too would be wondering about this. i'd say 40-50 degrees on a steep climb would be more typical.

Wed Feb 03, 2010 10:02 am

Quote: It might be comforting, but I'm pretty sure you're not getting the whole story.

x2

i was pretty comfortable when my DD used to read 300 going 65 on the freeway. then one day i changed my plugs, which reseated the sender. now i see 360-370 doing the same speed, which i think is much more accurate. i can easily hit 400 if i try to do 70 for very long. (which i dont) i also see 10 degree fluctuations just going over overpasses on the freeway. no hills here in houston...

the scary thing is that all the while i was reading those 300 temps, i had no fear of going 70, or 75. why the hell not, look how cool its running! who knows what damage i did.

ive found the whole CHT gauge deal to be pretty tricky business, who knows for sure whats really going on. the DD is a whole lot better than the VDO, i will say that.

Wed Feb 03, 2010 11:42 am

The ring on my sender broke off about 6 months ago. Driving my bus has not been this pleasant since, well, since before I installed the CHT gauge.
I don't need a weatherman to know which way the wind is blowing and I don't need a gauge to tell me when I'm pushing my engine too hard.

Wed Feb 03, 2010 2:36 pm

Quote: I'd bet a dollar that something is not right with your set-up

What could be not right about my setup?

This gauge and sender have been acting like this since new. Wires are correctly connected (connect them backwards and there is no reading on the gauge), connector plug is clean and tight, sender ring is firmly seated under the spark plug, no cuts in wire insulation, no loose or broken wires near the bend in the ring.

If you get through to VDO tech support, they act like it's OK to sell something they know doesn't always work the way it should.

My first VDO CHT gauge and sender lasted fifteen years and it usually ran just about 360F with the kind of swings Patrick and Scott mentioned.

Maybe I just got a bad one, but after this it will hurt even to try a new sender.

Wed Feb 03, 2010 6:16 pm

raymino wrote: Quote: I'd bet a dollar that something is not right with your set-up

What could be not right about my setup?

This gauge and sender have been acting like this since new. Wires are correctly connected (connect them backwards and there is no reading on the gauge), connector plug is clean and tight, sender ring is firmly seated under the spark plug, no cuts in wire insulation, no loose or broken wires near the bend in the ring.

If you get through to VDO tech support, they act like it's OK to sell something they know doesn't always work the way it should.

My first VDO CHT gauge and sender lasted fifteen years and it usually ran just about 360F with the kind of swings Patrick and Scott mentioned.

Maybe I just got a bad one, but after this it will hurt even to try a new sender.

Is that cylinder "pulling its weight"? If it is not firing properly it may be running cool. What happens when you remove the #3 lead with the engine idling? There should be a noticeable drop in revs and that should be replicated on the other cylinders.

Wed Feb 03, 2010 9:20 pm

In my experience, VDO CHT gauges are not accurate. Don't get me wrong, I love the VDO stuff, but the VDO CHTs in particular do not give a reliable reading. I hate digital gauges, but have found the Dakota Digital one to be pretty accurate. I'll take accuracy over aesthetics since it is such a critical gauge.

You may find this article helpful: http://www.ratwell.com/technical/VDOGauges.html#cht

-B

Wed Feb 03, 2010 9:47 pm

braidmeister wrote: In my experience, VDO CHT gauges are not accurate.

i've seen plenty of odd behaviour with DD gauges. they are not any better than anything else on the market in my opinion, and yes they are butt ugly. the sender to harness connection of the DD CHT is awfully engineered also, and a potential source for issues.

the biggest issue with the VDO CHT gauges is that there can be significant (like 30 degrees or thereabouts) variation between gauges. meaning if you hook up several gauges you could see variation between them, all else being equal.

Wed Feb 03, 2010 10:16 pm

Got my infrared thermometer tonight. I'll check out the temp after driving to work in the morning.

My thought was to note the gauge reading when I stop the bus, open the hatch above the engine, yank off the spark plug wire and shoot down the hole to get a reading. The meter has a 1" diameter reading from 12" away so I need to get down pretty close to the plug. Sound about right?

Thu Feb 04, 2010 8:02 am

mnskmobi wrote: Is that cylinder "pulling its weight"? If it is not firing properly it may be running cool. What happens when you remove the #3 lead with the engine idling? There should be a noticeable drop in revs and that should be replicated on the other cylinders.
Yeah, what if the gauge is reading right?! I will try your suggestion. Plug on #3 looked good in a recent inspection and motor runs fine. Too bad I can't move the sender to #4 or #1. I think that you cannot make the wire to the cab longer by splicing in another section.

bedfordd wrote: Got my infrared thermometer tonight. I'll check out the temp after driving to work in the morning.

My thought was to note the gauge reading when I stop the bus, open the hatch above the engine, yank off the spark plug wire and shoot down the hole to get a reading. The meter has a 1" diameter reading from 12" away so I need to get down pretty close to the plug. Sound about right?

Looking forward to seeing your results. What kind of meter did you get?

Patrick199 wrote: I don't need a weatherman to know which way the wind is blowing and I don't need a gauge to tell me when I'm pushing my engine too hard.

X2. I mostly want it just for long term monitoring and observing the effect of timing/tuning changes. After a while you get to know when to back off or downshift. I guess since mine is acting so flakey it bothers me.

braidmeister wrote: I'll take accuracy over aesthetics since it is such a critical gauge.

My VDO CHT gauge sits in the clock block off plate and kind of looks like it belongs there. I agree with Scott ... a DD just wouldn't fit on my dash. Thanks for the Ratwell link, I hadn't read it for a while. As I Understand it, the thermocouple action of the sender generates millivolts. Ratwell and others have shown us how to check out a fuel gauge sender by measuring resistance in different situations, same with TS II. Why can't we get information on the expected mV from the sender? It seems the gauge itself is just some kind of mV meter, and is somehow calibrated to the expected mV from the sender. Can a regular VOM even measure mV?

germansupplyscott wrote: the biggest issue with the VDO CHT gauges is that there can be significant (like 30 degrees or thereabouts) variation between gauges. meaning if you hook up several gauges you could see variation between them, all else being equal.

Agree. I can accept the variation in gauges and believe in using it just for relative observation. I know I should be getting wider swings on the hills, though. Destroys my confidence in the gauge. Makes me think about replacing it with German Supply's oil temp setup. Just can't see myself pulling into the car wash bay, drenching the bottom of my engine with Gunk, then car wash engine cleaner, then soap, then rinse. Oh, the pain of subjecting that poor sender and wire to all that!

Thu Feb 04, 2010 8:28 am

thats why you test em in boiling water by pulling the O ring in and reading what it reads. I have two VDO CHTs and one reads dead on the other 30F too low....
I tested the DD gauge before I installed it to test it, right on. So its reading in the Westy are between 360-410F driving upto 75mph...and it depends on how cool it is outside. If its cold and wet in the 40'sF, its gonna read in the low 300'sF.

Thu Feb 04, 2010 12:58 pm

Quote: My thought was to note the gauge reading when I stop the bus, open the hatch above the engine, yank off the spark plug wire and shoot down the hole to get a reading. The meter has a 1" diameter reading from 12" away so I need to get down pretty close to the plug. Sound about right?

This is a waste of time and energy.
The cylinder head will cool considerably by the time you get back there with your thermometer. By the time you get a spark plug out, forget it.
Use the boiling water method.

Quote:
Makes me think about replacing it with German Supply's oil temp setup.

Oil temp and CHT have little affect on or relation to each other. Oil temp and oil pressure go hand in hand. You can watch one go down (OP) as the other goes up (OT). If I could have just one gauge, it would be one of those two.

Quote:
Just can't see myself pulling into the car wash bay, drenching the bottom of my engine with Gunk, then car wash engine cleaner, then soap, then rinse. Oh, the pain of subjecting that poor sender and wire to all that!

Why not?
It won't hurt anything.

Why am I so negative?
CHT gauges just bring out the worst in me. The whole ring-around-the-spark plug thing seems ridiculous. I'll take a properly seated spark plug over an untrustworthy gauge any day.
Besides, most of us know when we are pushing the limits of our engines. If your engine is going to suck a valve, it's going to suck a valve. The gauge won't stop that. Might as well just get it over with.

Thu Feb 04, 2010 1:15 pm

Patrick199 wrote: The whole ring-around-the-spark plug thing seems ridiculous. I'll take a properly seated spark plug over an untrustworthy gauge any day.

X2

I think that Ratwell brings up a good point about extending the thermocouple line itself. You'd think in this day & age that we could get ahold of a good, accurate and reliable (from one gauge to another of the same model) setup. I'd like to have an accurate/true gauge, but won't be zip-tying a Fluke meter to the dash...Aside from oil pressure, it's the most critical gauge on the car.

-Brady