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IO-390 - #4 is about 50deg cooler CHT

B

BHunt

Well Known Member
I recently bought an 8 with a Barrett IO-390. Runs great, but the #4 CHTs are consistently 50 ish degrees cooler than #1-3 at cruise. I see about 350 on #1-3 and about 298 on #4. The EGT on #4 is about the same as the rest of the cylinders. I tried searching through threads, but couldn't seem to really dial in the same issues and the thread from earlier didn't quite seem it either... let me know if I am missing something. I also have pics from cruise that I can upload.

Thanks a lot!
 
4 gets the most cooling flow

For the angle valve IO390... Look carefully at the cooling fin locations on the cylinders... from the orientation that they attach to the engine you will see that 1 and 3 have forward facing fins and 2 and 4 have the the fins facing aft... with this arrangement cylinder 4 gets extra cooling from the fins on 2 at the front and its own fins aft. Cylinder 3 is deadheaded aft and is typically the hottest. You can adjust the temps a bit by working the forward facing baffle plates on 1 and 2 and adding some flow diversion to the back of 3. I have a spread of around 35 degrees from 3 to 4.
 
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You might want to swap CHT probes to confirm before diving into baffle changes, just to confirm.
 
I put a washer behind the #3 baffle and my #4 is the hottest. However, that wasn't the case before I made my oil cooler cut-out behind #4 larger.

In addition to verifying your probes are reading correctly, I would also consider mixture distribution. If you are running LOP and the #4 is leaner than the others, this will account for some of the lower CHT. However, it would have to be a large delta to account for a 50* difference.

You should also check your compression on #4. You could have a leak at one of the valves creating low compression. This would reduce CHT, if the leak was considerable. However, I would think you would notice the effects. Given this is a new to you engine, it is possible as you wouldn't have a benchmark to compare to.

Larry
 
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angle valve...

Note that the cylinder shape and fin arrangement is quite different between the angle valve and parallel valve cylinders...

OP question is specific to the angle valve IO390
 
BHunt said:
My #3 is the hottest. Could you explain more why what I have doesn't make sense?.
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Unless I cant read, which is likely, you said 1-3 are the same and 4 is coolest, and it was 4 you were asking about. No where did you mention 3 as an issue. I was just noting that what you have is not typically what people see, and its also odd that your EGTs are all the same despite your CHTs. Just seems to point to a CHT probe being suspect (or both 3&4 probes) vs a cooling issue. That's all.
 
maniago said:
Unless I cant read, which is likely, you said 1-3 are the same and 4 is coolest, and it was 4 you were asking about. No where did you mention 3 as an issue. I was just noting that what you have is not typically what people see, and its also odd that your EGTs are all the same despite your CHTs. Just seems to point to a CHT probe being suspect (or both 3&4 probes) vs a cooling issue. That's all.
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You're right. #3 isn't an issue. That's why I was confused when you brought up #3 typically being the hottest and what I had not making sense. Care to elaborate on how your earlier response makes my situation unusual? I'm honestly curious/ trying to learn, but your earlier response didn't really address my question.
 
BHunt said:
You're right. #3 isn't an issue. That's why I was confused when you brought up #3 typically being the hottest and what I had not making sense. Care to elaborate on how your earlier response makes my situation unusual? I'm honestly curious/ trying to learn, but your earlier response didn't really address my question.
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Ah. I agreed with Raymo inthe first post - check your probes first. The rest of my response was qualifying why I thought that checking probes made the most sense - because bad probes would give you non-typical results. If it got confusing, I apologise - I'm probably badly guilty of typing out loud.
 
maniago said:
Ah. I agreed with Raymo inthe first post - check your probes first. The rest of my response was qualifying why I thought that checking probes made the most sense - because bad probes would give you non-typical results. If it got confusing, I apologise - I'm probably badly guilty of typing out loud.
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That makes sense. I will check that route just to be safe.
 
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