CHT temps

Dgrainco · #1 10-16-2018, 07:38 PM

Just purchased an RV6A with IO-360 Lycoming. Climbing out at 1200 fpm no 4 cht goes to 425 other cht?s under 400. One person told me this is the nature of the beast. I have no experience with this and thought it seemed a bit on the high side. When I level off to cruise it runs about 360. Should I be satisfied with this or look for improvement?

Kyle Boatright · #2 10-16-2018, 08:37 PM

That's fairly typical. Use the high climb rate to clear obstacles, but otherwise, cruise climb at 120 knots or more to keep temps down.

However, there is every chance that your airplane isn't optimized for cooling, so you probably want to ask an experienced builder to help you find and fix any problems that would impact cooling. Baffle leaks, for instance.

AlexPeterson · #3 10-17-2018, 06:15 AM

Welcome to the world of RV's and to VAF!

There is perhaps more written about CHT's in these forums than any other subject. Set aside a day or two to search and read through the numerous threads on the topic.

N941WR · #4 10-17-2018, 06:34 AM

Read the Lycoming Operating Handbook for your engine.

The max CHT numbers are much higher than you would think.

Latech15 · #5 10-17-2018, 06:48 AM

I have cowl flaps from anti-splat installed on my 6A and since I replaced a faulty cht probe, I haven?t seen anything over 400.

meyer228 · #6 10-17-2018, 01:30 PM

I went through this a few years ago. Reach inside the front of the cowling inlets and feel if the inboard side of the upper ramps are sealed. If not, it's a fairly easy fiberglass effort. Some builders put baffling to cover these holes. Mine were wide open and a bunch of cooling air must have been escaping because when I seal them my temps went down 20 degrees.

Mark33 · #7 10-17-2018, 05:35 PM

Quote:

Originally Posted by Latech15

I have cowl flaps from anti-splat installed on my 6A and since I replaced a faulty cht probe, I haven?t seen anything over 400.

I?ll be incorporating the anti-splat cowl flap on my new -7 build. How much did your temperatures drop after installing one on your 6A? Also, did you install one or two?....I?m only going to install one.

Mark

lr172 · #8 10-17-2018, 08:55 PM

I would say that something is either not right or can be improved. I would start with baffling issues as that is the most likely reason. CHTs of 425 are not the "nature of the beast" for a well setup 6.

My 6A with an IO-320 climbs 1000-1500 FPM with CHTs below 375 in the heat of Summer. CHTs are pretty evenly distributed ( + or - 10*), though the distribution changes between climb and cruise.

You can likely do better with an investment of time improving your baffling. And if a baffling re-hab doesn't address it, I would then look for reasons in the engine. Be sure to experiment with different size blocking plates in front of #2

As mentioned, a search will produce some guidance.

Larry

KeithB · #9 10-18-2018, 08:45 AM

I flew an RV-6A with an O-360 for 3 years. It exhibited similar CHT problems as described and I implemented many ?fixes? - RTV sealing of the baffles, filing of casting flanges between fins on cyclinders, altered front baffle deflectors (to better balance front to back air distribution), closing the open inlet ramps, better cowl seal material. All had positive affects, but I still had to watch my climb speeds (> 120 knots) and used step climbs in more extreme conditions (high DA, high outside temps, full load, etc). Due to a cyclinder AD, I did a top end overhaul (new Millenium cylinders). During this overhaul I found two cylinders where one of the compression rings was broken. All cylinders were making compression (one with a broken ring was consistently over > 70 psi, the other in 60s). After the top overhaul, all CHTs dropped by 20-40 degrees.

I offer this history not to scare people with CHT issues - it does NOT mean you have to do a top overhaul. However, everyone should be aware that high CHTs are not always solved by easy fixes, and can be symptomatic of bigger issues.