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DougB
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Joined: January 09, 2007
Posts: 1077
Location: Falls Church, Virginia, USA
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 Posted: Mon Jan 13, 2014 11:29 am Post subject: Diff between CHT readings between cyls #1 and #3? |
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Hello all,
OK, I mistakenly installed my CHT sender on cyl #1 (front of engine, right side) instead of cyl #3 (front of engine, left side). I can switch the sender location (probably...there was not much slack in my 18' sender wire), but wanted to ask first: what would the temp difference be between cylinders #1 and #3? I searched but couldn't find the temp comparison that I thought someone posted a while ago.
Thanks,
- Doug
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aeromech
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Joined: January 24, 2006
Posts: 17638
Location: San Diego, California
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| Posted: Mon Jan 13, 2014 11:49 am Post subject: |
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That's going to be hard for someone to answer because most people don't monitor more than just one cylinder. I'd say just leave it when it is and it will be fine. some engines monitor all cylinders but I think for the most part you're just trying to get a trend of what's happening on a trip. In other words, you start climbing a mountain. Watch the cht and when it starts approaching the limit you tell yourself to back off on the throttle. This should work the same no matter what cylinder you're monitoring. Not sure what engine you have but the whole #3 runs hottest was from the type 1 non-doghouse style cooler blocking that cylinder. If you have a T4 engine or a doghouse T1 I'm not so sure if it matters which cylinder you have your sender mounted on.
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SGKent 
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Joined: October 30, 2007
Posts: 42521
Location: at the beach
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| Posted: Mon Jan 13, 2014 11:55 am Post subject: |
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| As Gary said - #3 on single port has an oil cooler in the flow so it runs hotter. 3 and 4 on a pancake split part of their air off to the oil cooler so they might be a tad hotter. I think that over the years mechanics noticed that cylinder #3 was more prone to failure so that is where we monitor. It really depends on what you want. Some folks don't even want to be upset by gauges whereas others want every cylinder monitored for temp, EGT and head temp. I monitor #3 CHT for 2 reasons - (1) it helped me tune the engine (2) it tells me when I am pushing too hard. Beyond that we use our bus as a Sunday driver. It is a 40 year old collector car. Our days of daily driver in a bus are over. The speed limit here is mostly 70 and in some states 80 now. Bus can't keep up in those conditions. |
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DougB
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Joined: January 09, 2007
Posts: 1077
Location: Falls Church, Virginia, USA
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| Posted: Mon Jan 13, 2014 12:07 pm Post subject: |
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Thanks all (and for not suggesting that the post be relegated to the "stupid questions" sticky 
I have a 2.0L FI Type 4 engine (a Raby Camper Special) in my '75, so that's the engine I'm monitoring. So far I haven't seen a CHT reading above 280 degrees F, though that was on a 55 degree day.
What would you all recommend I use as my "alarm" limit? I programmed 400 degrees F into the DD CHT as the point to sound the alarm...sound right?
Thanks again!
- Doug
_________________
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'73 Fastback
'52 BMW R67/2
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aeromech
Samba Member
Joined: January 24, 2006
Posts: 17638
Location: San Diego, California
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| Posted: Mon Jan 13, 2014 12:27 pm Post subject: |
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Why don't you ask Jake?
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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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| Posted: Mon Jan 13, 2014 2:54 pm Post subject: |
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Your number seems low to me. Are you intalling the sender around the spark plug?
Mine runs at about 350-380º most of the time and is set to flash at 400º. |
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SGKent
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Location: at the beach
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| Posted: Mon Jan 13, 2014 3:15 pm Post subject: |
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| Randy in Maine wrote: |
Your number seems low to me. Are you intalling the sender around the spark plug?
Mine runs at about 350-380º most of the time and is set to flash at 400º. |
I agree with Randy. The general consensus is that 350 - 380 F at the plug is normal. 280 F would be low unless the sender is bolted closer to the fins. Mine idles at 350 F at the #3 plug which is where the thermostat holds it. It remains below 380 F most of the time unless I am pulling a headwind, grade or pushing it above 65 MPH. The speed limit in the USA was 55 MPH when these buses were made. That law was in effect from 1973 to 1995. |
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60's Burnout
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Joined: December 10, 2006
Posts: 424
Location: SF Bay Area
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| Posted: Mon Jan 13, 2014 6:41 pm Post subject: |
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| DougB wrote: |
Thanks all (and for not suggesting that the post be relegated to the "stupid questions" sticky
I have a 2.0L FI Type 4 engine (a Raby Camper Special) in my '75, so that's the engine I'm monitoring. So far I haven't seen a CHT reading above 280 degrees F, though that was on a 55 degree day.
What would you all recommend I use as my "alarm" limit? I programmed 400 degrees F into the DD CHT as the point to sound the alarm...sound right?
Thanks again!
- Doug |
Wow, you're one of the 55. That's a really elite group. I think you should buy the aircraft style CHT. It monitors all 4 cylinders and has better accuracy. $20,000+ engines deserves that...Then put a pitot tube on it. Don't buy the one Airbus uses, you'll crash into the ocean... |
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aeromech
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Joined: January 24, 2006
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Location: San Diego, California
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| Posted: Mon Jan 13, 2014 6:46 pm Post subject: |
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Don't buy the one Airbus uses, you'll crash into the ocean...
That was a terrorist bomb cover up much like flight 800.
http://www.washingtonsblog.com/2013/08/the-missiles-that-brought-down-twa-flight-800.html
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
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Jake Raby
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Joined: August 23, 2003
Posts: 7433
Location: Aircooled Heaven USA
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| Posted: Mon Jan 13, 2014 7:17 pm Post subject: |
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| DougB wrote: |
Thanks all (and for not suggesting that the post be relegated to the "stupid questions" sticky
I have a 2.0L FI Type 4 engine (a Raby Camper Special) in my '75, so that's the engine I'm monitoring. So far I haven't seen a CHT reading above 280 degrees F, though that was on a 55 degree day.
What would you all recommend I use as my "alarm" limit? I programmed 400 degrees F into the DD CHT as the point to sound the alarm...sound right?
Thanks again!
- Doug |
That sensor MUST be on #3. You'll see that temps rise 30-50* immediately.
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Jake Raby
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DougB
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Location: Falls Church, Virginia, USA
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| Posted: Mon Jan 13, 2014 7:33 pm Post subject: |
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Roger, I'll make the change tomorrow. Thanks!
- Doug 
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Jake Raby
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Joined: August 23, 2003
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Location: Aircooled Heaven USA
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| Posted: Mon Jan 13, 2014 7:40 pm Post subject: |
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| DougB wrote: |
Roger, I'll make the change tomorrow. Thanks!
- Doug |
#3 is always hottest, #1 is generally coolest. With stock cooling a 30+* delta is normal.
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Jake Raby
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VDubTech
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Joined: December 29, 2002
Posts: 9156
Location: Syracuse, NY
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| Posted: Mon Jan 13, 2014 7:49 pm Post subject: |
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| SGKent wrote: |
| \The speed limit here is mostly 70 and in some states 80 now. Bus can't keep up in those conditions. |
Bullshit. A Bay Window Bus can, will, and was designed to go 75 all day long.
| SGKent wrote: |
| The speed limit in the USA was 55 MPH when these buses were made. That law was in effect from 1973 to 1995. |
The national speed limit was raised in 1987 and 88 to 65mph and the law was repealed in 95 when Congress gave that right back to the states.
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sambabus
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Joined: December 02, 2009
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Location: N. Cal
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| Posted: Mon Jan 13, 2014 8:04 pm Post subject: |
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I found this article to be interesting:
http://www.liquidcooledairpower.com/lc-topendheat.shtml
Not for the water cooled part, but the air cooled.
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udidwht
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| Posted: Mon Jan 13, 2014 10:27 pm Post subject: |
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| VDubTech wrote: |
| SGKent wrote: |
| \The speed limit here is mostly 70 and in some states 80 now. Bus can't keep up in those conditions. |
Bullshit. A Bay Window Bus can, will, and was designed to go 75 all day long.
| SGKent wrote: |
| The speed limit in the USA was 55 MPH when these buses were made. That law was in effect from 1973 to 1995. |
The national speed limit was raised in 1987 and 88 to 65mph and the law was repealed in 95 when Congress gave that right back to the states. |
States were given the right to raise them but a lot of them did it over time. It wasn't automatic. As states raised them it was set according to areas of flow. It wasn't 65mph across the board. Also baywindows were NOT designed to go 75mph all day everyday. One has to only look at the countless souls over the decades who've lost their beloved bus/camper due to dropped seats or thrown valves to know that. Yeah, yeah...I know it states in the manual that it's crusing speed is ...BS! Don't believe everything you read. They didn't mean that quite literally.
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DougB
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Location: Falls Church, Virginia, USA
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| Posted: Tue Jan 14, 2014 12:37 pm Post subject: |
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OK, sender swapped to cyl #3...I didn't immediately notice any significantly higher readings during my quick drive at lunch today, but that trip wasn't likely long enough.
One thing that I really appreciate about the CHT is the ability to know when the engine has reached the desired operating temp at warm up (which I've been doing religiously since installing the engine).
I have to say that of all the gauges I have installed right now the least useful seems to be the oil temp...perhaps on long, long trips it will be more useful, but the VDO version I'm running just doesn't register fast enough. I'll definitely be following the CHT readings more than anything once summer rolls around.
Onto the next project: installing the Bosch intermittent wiper relay!
- Doug
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'73 Fastback
'52 BMW R67/2
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SGKent
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Location: at the beach
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| Posted: Tue Jan 14, 2014 4:11 pm Post subject: |
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| udidwht wrote: |
| VDubTech wrote: |
| SGKent wrote: |
| \The speed limit here is mostly 70 and in some states 80 now. Bus can't keep up in those conditions. |
Bullshit. A Bay Window Bus can, will, and was designed to go 75 all day long.
| SGKent wrote: |
| The speed limit in the USA was 55 MPH when these buses were made. That law was in effect from 1973 to 1995. |
The national speed limit was raised in 1987 and 88 to 65mph and the law was repealed in 95 when Congress gave that right back to the states. |
States were given the right to raise them but a lot of them did it over time. It wasn't automatic. As states raised them it was set according to areas of flow. It wasn't 65mph across the board. Also baywindows were NOT designed to go 75mph all day everyday. One has to only look at the countless souls over the decades who've lost their beloved bus/camper due to dropped seats or thrown valves to know that. Yeah, yeah...I know it states in the manual that it's crusing speed is ...BS! Don't believe everything you read. They didn't mean that quite literally. |
We've driven cross county enough to know that the speed limit is not the same from state to state and I agree with udidwht as to how the speed limit was changed. Even today it is not uniform.
http://en.wikipedia.org/wiki/File:US_speed_limits13.svg |
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