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Low CHT

Adam

Well Known Member
I'm one of the guys that has a problem with a low CHT. I know many of you have high CHTs and high oil temps put I have the opposite issue. I have a standard Vans cowl with an Superior I0-360,, on days that the temp is say 75 degrees my CHT is usually from 250 to under 300. On cold days my run up temps are higher then my in flight temps. I have checked all my probs and they read correct. My issue is that because the cylinders run so cool I get cokeing of the valve guides. What is the best way of dealing with this?
 
I'm one of the guys that has a problem with a low CHT. I know many of you have high CHTs and high oil temps put I have the opposite issue. I have a standard Vans cowl with an Superior I0-360,, on days that the temp is say 75 degrees my CHT is usually from 250 to under 300. On cold days my run up temps are higher then my in flight temps. I have checked all my probs and they read correct. My issue is that because the cylinders run so cool I get cokeing of the valve guides. What is the best way of dealing with this?

What makes you think they are too low? Is this a low compression engine? The Superior cylinders do for some reason run cooler, better fins and less flashing etc maybe? DanH might have some wise words on that.

As for cooking of the valves, please qualify what you mean by that. Otherwise it seems fine to me.
 
Oil coking is a high temperture condition (think burnt oil) and generally assoiciated with turbines in my experience. If you are suffering from sticky valves this is generally caused by lead contaminated oil /failure to lean.

Low CHT's are fine (better than high CHT's), your temps are nothing to be concerned with especially in the winter.
 
Your right about cokeing that would be a hot oil issue,, the problem is that there is a lead build up on the valve guides that causes a sticky valve and the engine to shutter every so often. I lean all the time and fly lean of peak. My concern is that because the temps are so low the lead dose not get burned off.
 
I've heard that running LOP allows lead deposits to build up and that You should also run some higher power settings intermittently to help clean off these deposits. I have no facts just word of mouth, perhaps someone else...
 
LOP operations do not cause lead or Lead Oxybromine deposits to be any worse, in fact they are better.

Valve guides could well be an issue from manufacture, and I would suggest that any talk of the contrary is a smoke screen. Otherwise I can show you thousands of engine all stuck up and failing........Nope not happening.

Oil issues maybe....

Walt is right.....
your temps are nothing to be concerned with especially in the winter.
 
Too low

I have a Superior IO360 also and your temps seem unusually low to me. I am curious as to why. Efficient cooling is great, but you are running 75 to 100 f cooler than most. Are you confident you are making full power? Confident in your gauges/probes? Running overly rich? There must be something else going on here.
 
As a point of reference my ECI runs around 280-300F during cold weather (cold to me is <50F, I don't usually fly when its less than 40F).
I rarely see anything above 350 even in the Texas summer heat.
The above is typical at my cruise power of 65%
 
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On a 75 f day at 60 percent power, my cht s are about 345 f. The other day at 32 f, my cht s were about 320. If I lop on a 75 f day, I can get down to 300 f at low power setting
 
Not Too Low

I have a Superior IO360 also and your temps seem unusually low to me. I am curious as to why. Efficient cooling is great, but you are running 75 to 100 f cooler than most. Are you confident you are making full power? Confident in your gauges/probes? Running overly rich? There must be something else going on here.

I have a stock lycoming IO-360 angle valve, and Adam's CHT's are in line with mine. I typically don't see anything over 360 on a hot day/full power extended climb, and my cruise CHT's run between 260-310F. This is with the stock cowling and baffles, except that my oil cooler (stock vans FWF Niagara) is mounted behind #3 instead of #4.

Skylor
RV-8
 
low cht

Adam, you are not alone. My O-320 never hits over 370 on summer climb out, and cruised at from 200f to 325f. I called Lycoming and he said, "Lucky You, your cylinders will last forever!" His words were, don't worry till they get down to 150f, then we need to do something. In the winter with 30f OAT, they get down 180-225f, especially if I am cruising around saving fuel at 5-6gph. I would love to get them a little higher.
Blocking off the exit does no good, tried that, by blocking off 60% of the area. The inlets are the key. IMHO (and yes I checked to probes).
49clipper
RV-6
 
Although there is nothing "wrong" with low CHT, you will give up free speed by flowing more cooling air than necessary.

Cooling mass x velocity loss = cooling drag

Blocking off the exit does no good, tried that, by blocking off 60% of the area. The inlets are the key. IMHO

You can reduce mass flow by shrinking the inlet, but doing so may result in reduced velocity at a large exit, thus no net loss of drag. Quite a few folks have been down that road.

Low cowl pressure + large exit area = low exit velocity

Exit area reduction incorporating shape beneficial to velocity increases speed. It also unquestionably throttles mass flow and provides CHT and oil temperature control if the area can be made variable.
 
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