#3 and #4 CHT's - PA30B

Postby William Coleman » Thu Jan 31, 2013 4:01 pm
I am running 410 to 420 CHT's on the rear Cyl's during climb with cowl flaps full open. I have re-sealed all the baffles including the front with new seals and is very tightly sealed including sealing all open spaces. Engine timing at at exactly 25. Oil temp is at 180 to 190 which is good. I have the JPI 760 monitor and the new Shadin fuel flow system. During the summer months this condition gets worse! Also during cruise I must run with the cowl flaps 1/2 open to keep 3 and 4 below 390. #1 and #2 run at 320 to 340. I also installed the Knots2U side air induction system which closed the 3 1/2 hole behind #3 which showed little improvement. Both engines have new Lycoming clyinders with appox. 150 hrs on them so they are fully broken in. The ring gaps were set to the middle of the gap tolerances. I use about 1 qt of oil every 35 to 50 hrs. Oil samples from Black Stone show very normal samples. WHAT more can I do? Does anyone share this problem or can offer more suggestions? I don't want the cylinder temps going above 400.

Welcome to the Forum, I see this is your first post.

First, I haven't seen this problem with either stock cowls or LoPresti cowls on my Twin.

Couple of thoughts - do you know of a time when the CHTs did not run hot on these cyls and if so, what changes were made right before they started do the hot thing?

Is this happening on both engines?

If it is, then I'd look for further indication that cyls are actually hot. What do the stock gauges read? What do the EGTs read. Is there any heat indications around the cyls?

How is the exhaust fit in these areas? Had mine O/H and then had a problem on #1 due to a bad fit that only showed up after 50 hours or so -caught it at annual inspection.

Are the engines aligned with the air inlets? if not, older Lord mounts could impact the orientation and air flow. Suggestion is to change every 4 years.

Being of a computer background, the assumption is the probes are sending accurate info should be checked. Perhaps the are seated differently for the aft cyls.

Have tried to cover things that have impacted my twin in the past - any chance the servo is shorting them on fuel? Might be another area to check.

Hope something hear gives you some help.

Everything you mentioned in your post has been investigated. However, researching my log books I have not been able to find where the engine mounts have ever been replaced. I'm placing an order for 8 of them. Considering how much I have already spent restoring and overhauling the engines, I have no excuse for not replacing them at overhaul. I guess it was just hard to accept $1100 for eight mounts...
Thank you for your response.

What cowls?... your picture is small but appears that your plane is beautiful.. I have not seen a better Robertson STOL paint design!

You say your baffles are tight... I accept that... but respectfully, it took me probably 2 years to get mine "frog butt tight". Gaps the combined size of a quarter can have a tremendous effect. Pay particular attention around where the oil temp therm is located on the right side of the engines... some early baffles have a gap where the baffle meets the engine hidden by the oil cooler. I closed a gap on the left front of the engine that even Hans told me I was getting anal about. I finally got a borescope to really see what the situation was with the cowling installed. It isn't easy.

Jim