Question for those of you with a digital CHT gauge Options

[era vulgaris]

For those of you who have a digital head temp gauge, what's your #3 cylinder temp after a good distance of highway running? Say like after 20 minutes between 3K5 and 4K RPM in 5th gear, or in the 70-80mph range?

Part of the reason I got my car with a 2270 for a proverbial song was because the PO was having serious issues with the engine running hot and I think he was a bit fed up with the car. I've spent a crap ton of time tuning the shit out of the carbs and engine, and also replacing a few sketch-ball parts he had on there. I can now run EZ-PZ in the 310-320F range on #3 all day long off the highway, up to 60 or 65mph.
But once I get on the highway and get above 70mph, my temps start climbing up into the 370's and even higher if it's an uphill grade.
I know it's a much greater load on the engine to push through the air at that speed, but the difference in temps seems abnormal. Or is it?

I'm wondering if the 916 bumper on my car might have something to do with it. Is it possible that the lower "splitter" part of the bumper is acting like an air dam, preventing cool air from getting under the car, and causing the temps to go up at higher speed?

Any insight is much appreciated! (IMG:style_emoticons/default/beerchug.gif)

[76-914]

I would see 340 when I ran one. How are your oil temps behaving. IOW, does the oil temp follow suit or stay the same? Good luck; it's what keeps 'em running.
EDIT: More importantly, did you verify the accuracy of the gage and sender?

[era vulgaris]

Oil temps are slightly higher after extended interstate running, but nothing that would be of concern. Only a few degrees.
I had a thought last night....I wonder if this could be due to the fact that I'm going 75mph with the top off and windows down. That's a hell of a lot of extra drag, which would create extra load for the engine. And that might explain the large change in head temps I'm seeing on and off the interstate.
I'm going to try a run today or tomorrow with the top on and windows up and see if there's any difference.

[76-914]

Do you have a wideband air/fuel gage as well?

[era vulgaris]

I do. My AFR hangs out in the high 11's to mid 12's while cruising.

[BeatNavy]

Well, you're definitely not "lean," so that's not causing it. Although referencing this thread: Type IV Temps, you're probably on the "high end" of acceptable and may need to assess some the cooling/tuning. Just curious, are you running an external oil cooler on your 2270?

[era vulgaris]

Yeah I've got an external oil cooler with electric fans. The fans are thermostatically controlled, and the cooler is using the Tangerine external take off kit.

Yeah I've seen that chart. I'm just stumped as to why my temps are fantastic up to about 65mph, and then after I get on the interstate they go up. It's got to be something related to the speed, because otherwise they would be high all the time.

[stugray]

If you are detecting no ping (knock) when the temps read that high, I would suspect the temp sensor/gauge is not reading correctly.

Do you know what type of sensor & gauge you have?

Are you by chance running a lot of timing advance?

[era vulgaris]

I don't think there's any knock, but I can't hear anything other than wind at 75mph with the top off and windows down!

It's an MGL Stratomaster Velocity 4 channel digital gauge. It's actually designed for aircraft use. I've got a sensor under each spark plug so I can monitor every cylinder.

Timing is 28 degrees BTDC.

[toon1]

so many things affect head temps, top down is one, there is extra drag( i noticed 3mpg drop with the top down), crosswinds are huge on head temps. Running high rpms ( like at 70-75) will raise them (as you know) but it also increases the wind resistance that the car has to overcome. that goes up by the square.

I don't think the 916 bumper is causing issues.

JMHO....you are too rich at those speeds. you have too much fuel that is still burning on the way out raising your EGT's and creating heat.

I'm finding that the "needs to be rich to stay cool" thing is not what people think it is.

[76-914]

you want to see 13.5-12.9 on the gauge while accelerating or climbing, 12.8-12.5 at WOT, and 16-17 while cruising, going downhill or decelerating.
Generally heads temps are 265-365 F
375 to 395 F is getting warm
405 F being too hot

Oil temperature
180 - 220 F is optimum
225 - 235 F is warm
235+ F is too hot.

(IMG:style_emoticons/default/beerchug.gif)

[Mark Henry]

you want to see 13.5-12.9 on the gauge while accelerating or climbing, 12.8-12.5 at WOT, and 16-17 while cruising, going downhill or decelerating.
Generally heads temps are 265-365 F
375 to 395 F is getting warm
405 F being too hot

Oil temperature
180 - 220 F is optimum
225 - 235 F is warm
235+ F is too hot.

(IMG:style_emoticons/default/beerchug.gif)

I agree 12.5 to 13.5 at load and WOT, I aim for just under 13.
16-17 while at cruse is way too lean, 14 would be my max. In fact I see head temps rise the leaner it gets at cruse, I try to run at 13.5.
Decelerating, anytime the the throttle is closed no load (excluding idle) the reading is irrelevant.

Ed are you running both the external and stock oil coolers?

[Bills914-4]

I don't think there's any knock, but I can't hear anything other than wind at 75mph with the top off and windows down!

It's an MGL Stratomaster Velocity 4 channel digital gauge. It's actually designed for aircraft use. I've got a sensor under each spark plug so I can monitor every cylinder.

Timing is 28 degrees BTDC.

question,
sorry if a little OT , do you run the the stock cooling shroud system, if you do , can I ask
what kind of temp differences between the cylinders do you get ? thank you Bill D.

[toon1]

you want to see 13.5-12.9 on the gauge while accelerating or climbing, 12.8-12.5 at WOT, and 16-17 while cruising, going downhill or decelerating.
Generally heads temps are 265-365 F
375 to 395 F is getting warm
405 F being too hot

Oil temperature
180 - 220 F is optimum
225 - 235 F is warm
235+ F is too hot.

(IMG:style_emoticons/default/beerchug.gif)

This is about what I'm seeing also. Although I like about 14.5, 14.7:1 at cruising. seems to give the best MAP reading so far. anything leaner makes the MAP readings go up.

[gereed75]

Sorry. Did not read the referenced thread so sorry if this redundant.

First off I would say that the cooling airflow through the cooling shroud is driven by pressure differential. The air travels from areas of high pressure to low. The delta P is not large ( Evan with the fan helping). So any disturbance of the delta P can cause a significant change in flow through the system. It is a system - shroud, fan, cylinders, engine compartment, car underside etc. I suspect that #3 has some local stuff occurring that effects local airflow. Again it does not take much

Secondly 400 degrees is the consensus number for aluminum heads in the aircraft world.where such things are oft discussed. Anything below is good

There is much discussion in that world concerning CHT, mixture, timing, peak combustion pressure, AFR and particularly EGT. They are all closely inter dependent. If interested go to the Vans Airforce Website in the general discussion forum and search LOP. Lean of peak (EGT) operations is analogous to our cruise. Hours of informative reading there from some smart guys who work with these issues all of the time

[era vulgaris]

you want to see 13.5-12.9 on the gauge while accelerating or climbing, 12.8-12.5 at WOT, and 16-17 while cruising, going downhill or decelerating.
Generally heads temps are 265-365 F
375 to 395 F is getting warm
405 F being too hot

Oil temperature
180 - 220 F is optimum
225 - 235 F is warm
235+ F is too hot.

(IMG:style_emoticons/default/beerchug.gif)

I agree 12.5 to 13.5 at load and WOT, I aim for just under 13.
16-17 while at cruse is way too lean, 14 would be my max. In fact I see head temps rise the leaner it gets at cruse, I try to run at 13.5.
Decelerating, anytime the the throttle is closed no load (excluding idle) the reading is irrelevant.

Ed are you running both the external and stock oil coolers?

I'm only running an external oil cooler. But with the tangerine remote kit, I have the block off piece which compensates the cooling airflow for there not being a stock oil cooler in place.

Yeah, I was running mid 12's to mid 13's AFR originally, but dropping it down to high 11's to mid 12's actually helped me run cooler head temps, which is why I took it down that low. While running mid 12's to mid 13's, I was in the 340F area around town. Dropping the AFR down brought my temps down to ~320F. Staying out of the 13's altogether really helped with my temps for driving around town.

[era vulgaris]

At any rate, I just got back from a run down the interstate again, this time with the top on and the windows up. I was running consistently in the 350F range on even level grades, which I think is definitely acceptable. Ambient temps were about the same as yesterday when I had the top off.
I guess that drag from the open cabin really made that much difference.

[era vulgaris]

I suspect that #3 has some local stuff occurring that effects local airflow.

#3 is always the hottest cylinder because it's the furthest away from the cooling fan. That's why that's the relevant cylinder to take readings from.

[era vulgaris]

I don't think there's any knock, but I can't hear anything other than wind at 75mph with the top off and windows down!

It's an MGL Stratomaster Velocity 4 channel digital gauge. It's actually designed for aircraft use. I've got a sensor under each spark plug so I can monitor every cylinder.

Timing is 28 degrees BTDC.

question,
sorry if a little OT , do you run the the stock cooling shroud system, if you do , can I ask
what kind of temp differences between the cylinders do you get ? thank you Bill D.

Yeah I've got the stock cooling setup. I'll have to look next time I'm driving to give you actual numbers. The gauge displays like a 4-channel bar graph and then you can choose which cylinder to specifically display a large number at the top of the gauge. I keep the number of #3 at the top since that's always the hottest.
At any rate, the bar graph looks kind of like a zig-zag with 1 and 3 being the hottest (3 being hotter than 1) and 2 and 4 being cooler. Makes sense since 2 and 4 are closer to the fan.

[toon1]

What weight oil?