Grumman CHTs?

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Whenskey

Filing Flight Plan
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Whenskey
Question for Grumman owners/operators:
I've heard before that the Grummans typically run hot because of the cowling design and cooling issues, and I've had some experience with this, but my question/concern is how hot is too hot? My dad and I recently put in a new engine in a Tiger, as the old one was original and pushing 40 years old. It ran hot, as expected, but never had any problems. We hoped that a new engine and better baffling would help everything run cooler, but it's still very hot as well. In the climb cylinders 1 and 3 seem to be the hottest, with 4 close behind, but in cruise 1 and 3 cool back down to low 400-410s, while number 4 seems to settle around the 430s. Number 2 usually always stays below 400. I will say that this is flying around in Florida in a warmer climate. I came down from the Philly area last month, and in the cold winter temps, nothing really got about 400 degrees in climb or cruise. I've been doing what I can to keep things cooler (faster cruise climbs, richer mixtures) but these CHTs seem rather excessive. I was just wondering what you other Grumman pilots have been seeing temperature wise, and what it normal for you?
 
Call Fletchair. There's a mod for the size and shape of the cowl air exit that lets more hot air out. I can't recall exact specs on it, but there's a hot air bubble that forms down under the baffling that can be fixed by modding the cowl exit area. I had a AA-5 with similar problem and my finding was there's also a gap up near the fresh air inlet that lets in hot air to the engine where there's usually very cool air. You may need a doubler seal on that air inlet to stop the hot air. Also, recheck the cutout for the oil cooler. Many planes got the 6 row cooler, but the cutout in the backing baffle plate was only shaped for the 4 row. Review your rubber baffle seals again, and also make sure there are deflectors under and between each pair of cylinders. The left side of my engine was missing the deflectors. After all my fixes in these areas the CHT and oil temps went down a lot.
 
You could also take a stick on foam block weather seal and create a 3/4" tall dam right in front of the lower cowl outlet (have the trailing edge be 125% the height of the bloc behind the block). This will reduce the pressure the exit flow runs into, and will probably be aerodynamically cleaner than opening up the hole. Stick it on and see how it works, that's what I did on the Traveller we were using for our gofer plane and it brought the CHTs down considerably. If it doesn't work you're out $5 at Home Depot.
 
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What EGT monitor, JPI or EI.
 
I know on the AA1s quite a few folks do the oil cooler addon.

400+ is toasty.

How is the baffling under the cowl?

Different bird, but I don't like anything over 380 on climb and 350 cruise.
 
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If it's over 400 in cruise this time of year, then you need better cooling (even with the JPI probes which tend to read higher). First thing to look at is the baffle seals, especially the ones around the front air dam, which often get overlooked. Also check for any gaps or other unsealed openings in in the baffling -- you may need some rubber gaskets around cable holes and the like.

The large gap between the prop spinner and the cowling is another place cooling air is lost -- there are several discussions on how to deal with that in the Grumman Gang archives if you look up "prop spinner gap seal". The LoPresti nose bowl alters that opening to dramatically reduce leakage there and reduces the cooling air losses by eliminating the induction air hole in the aft baffle.

Beyond that, Jim Candeletti came up with a mod to the lower cowl outlets to improve outflow. To my knowledge here's no STC or approval for it, but several people have done it with good results. You can find Jim through the Grumman Gang, too. However, contrary to what docmirror said, I don't know of anything Fletchair has done in that area, although they do have a field approval you can copy to mount a larger oil cooler -- they'll send a copy with the cooler if you buy it from them.
 
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Fletchair put me on to the Candeletti mod from a plane they had in the shop. I went down and took pics, and used a tape measure and stoinked it out. They had good things to say about the mod, and -- they are all things Grumman.
 
Whenskey said:
Question for Grumman owners/operators:
I've heard before that the Grummans typically run hot because of the cowling design and cooling issues, and I've had some experience with this, but my question/concern is how hot is too hot? My dad and I recently put in a new engine in a Tiger, as the old one was original and pushing 40 years old. It ran hot, as expected, but never had any problems. We hoped that a new engine and better baffling would help everything run cooler, but it's still very hot as well. In the climb cylinders 1 and 3 seem to be the hottest, with 4 close behind, but in cruise 1 and 3 cool back down to low 400-410s, while number 4 seems to settle around the 430s. Number 2 usually always stays below 400. I will say that this is flying around in Florida in a warmer climate. I came down from the Philly area last month, and in the cold winter temps, nothing really got about 400 degrees in climb or cruise. I've been doing what I can to keep things cooler (faster cruise climbs, richer mixtures) but these CHTs seem rather excessive. I was just wondering what you other Grumman pilots have been seeing temperature wise, and what it normal for you?
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Wondering if you ever fixed your CHT problem. My Tiger having identical issues in Florida.
 
A lot of time with the tiger it’s a baffling issue. Mine would run 385-395 inncruise dueing the summer. Any hotter and I would enrichen the mixture a little.
 
I had the same problem. My A&P/IA re-did all of my baffles - everyone - in between cylinders, around the starter, etc. Sealed all air leaks and then cut the back of the nosegear boot. He also installed a small air dam on the front of 1 & 2 cylinders to force more air towards the rear. Now, I rarely see 400 during a climb in the summer months and in cruise, typically see about 385 on the hottest cylinder which is #4. My temperature spread among the cylinders is a lot more even now. I also have a Powerflow Exhaust which adds more heat into the engine compartment. Find someone who really understands Grumman baffleing. You can add cowl flaps that are supposed to provide greater delta P, and you can also install larger cowl ducts. Gary Vogt at AU County sells them in fiberglass and I believe Fletchair sells them as well.
 
Although this is an old thread, the OP's temps are not normal. Poor baffling is the first place to look. My Tiger rarely goes over 400 during climb on a hot day (if I see it getting that hot I shallow out the climb and/or reduce power a little). I see 330-380s in cruise. I would recommend you have a IA very familiar with Grummans to help you out. I "think" True Flight in Valdosta is still around and servicing Grummans. Maybe give them a shout.
 
mr_happyland said:
Although this is an old thread, the OP's temps are not normal. Poor baffling is the first place to look. My Tiger rarely goes over 400 during climb on a hot day (if I see it getting that hot I shallow out the climb and/or reduce power a little). I see 330-380s in cruise. I would recommend you have a IA very familiar with Grummans to help you out. I "think" True Flight in Valdosta is still around and servicing Grummans. Maybe give them a shout.
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Thanks. Will do they are close enough. Had them inspected by my local guy but not the same as a Grumman specialist.
 
Joseph Costa said:
Thanks. Will do they are close enough. Had them inspected by my local guy but not the same as a Grumman specialist.
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What type of thermocouple do you have. I've got the ring type under the plug on my O-320. I'm not real sure I'm getting accurate readings. CHT's range from 275 to 325 in cruse the other day. OAT was around 20F.
 
The Tiger I had ran hot in summer, requiring enrichening quite a bit after max RPM take off here in the high DA southwest in summer. 420* would be the hottest I'd let it go before leveling for a short bit to cool. Baffles were done at FletchAIR as well as the exit ramp, but they never mentioned the air damns listed earlier.
 
Always been able to keep my temps in my tiger well below 400* even in 90*+ temps.
 
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we have a ag5b in the club with a new engine and even on cool days it runs 430 cht's. defintely have to watch the temps during climb.
 
Thanks for above comments. Getting it looked at by True Flight guys in Valdosta this Saturday. Lloyd is going to let me know what further work he would recommend doing after inspecting my Tiger. Will keep everyone updated if I make changes that help cool things down.
 
i will be looking for a tiger of my own soon so i will keep an eye out for your post.
 
Been a while since I owned a Tiger, but I do agree, they all run hot. Look into changing the lower spark plugs. Sorry, I can’t remember the numbers, but there is a longer (runs cooler) plug, that you put on the bottom. Makes starting on hot days easier also. You will definitely see an improvement. Good Luck.
 
docmirror said:
Fletchair put me on to the Candeletti mod from a plane they had in the shop. I went down and took pics, and used a tape measure and stoinked it out. They had good things to say about the mod, and -- they are all things Grumman.
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What does this mod look like? Does anyone have a description or photo of it?
 
Go to aucountry’s web site and look at his front strut boot replacement. Not only does it make removing the cowl easier but will drop your chts by a fair amount
 
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