High oil temperatures

[AaronJr]

I have a 1968 M20F with a modified J-model cowling and the cooler located at the back.

 

When I first bought the plane, my oil temperature was stable around 195°F. A few months later, it started staying between 205-210°F during cruise. During this time, I switched from 15W50 to 100W Plus oil, overhauled the oil cooler, and replaced the rubber seals around it, but none of these made any difference.

 

My CHT during cruise is normal, ranging between 360-370°F. I’m wondering if I should consider replacing the thermal valve?

[TaildraggerPilot]

What was the OAT during that climb? IAS? Cowl flap setting?

[AaronJr]

1 minute ago, TaildraggerPilot said:

What was the OAT during that climb? IAS? Cowl flap setting?

That’s during climb, full cowl flaps open.

23c

[TaildraggerPilot]

Those metrics seem pretty normal to me for a climb profile. Nothing is close to redline. Pro Tip:  120-130 IAS during climbs should provide you with the best cooling air flow with that J Cowl mod. What was your airspeed at that point? Do you have any shots of your JPI when settled down in cruise?

[AaronJr]

2 minutes ago, TaildraggerPilot said:

Those metrics seem pretty normal to me for a climb profile. Nothing is close to redline. Pro Tip:  120-130 IAS during climbs should provide you with the best cooling air flow with that J Cowl mod. What was your airspeed at that point? Do you have any shots of your JPI when settled down in cruise?

This picture (cruise)took from previous flight . All number are identical except the oil temperature (current) is around 205

[A64Pilot]

An indicator of high oil temps in cruise if everything else is fine is excessive blow-by, blow-by unfortunately doesn’t always show up in a compression check like you think it should.

If the oil turns coal black within a few hours of being changed you might have a stuck ring or similar.

Personally I climb my J at 120+ kts indicated primarily to keep cyl head temps where I like them, but of course it keeps oil temps low too. If anything I have an issue getting the oil warm enough, it’s never beyond the half way point on the gauge, but then I won’t let me cyl head temps get very high either. This was cruise the other day at 60% power or so LOP. It was cooler than average being Dec, but it was also in Central Fl and 4,500 so it’s not real cold.

 

[TaildraggerPilot]

All things being equal, if only the oil temp has changed, I’d look at the thermal valve. I wouldn’t worry about anything under 215, but that’s just me.

[markgrue]

First thing that comes to mind is the rtv on the oil cooler.   The air is supposed to circulate around the ends of the oil cooler through the fins there.  I personally prefer the 15-50 oil as it is a semi synthetic oil and I feel it lubricates better than the straight weight oils.  Just my opinion and it is worth just what you paid for it. 

 

Mark 

[AaronJr]

12 minutes ago, A64Pilot said:

An indicator of high oil temps in cruise if everything else is fine is excessive blow-by, blow-by unfortunately doesn’t always show up in a compression check like you think it should.

If the oil turns coal black within a few hours of being changed you might have a stuck ring or similar.

Personally I climb my J at 120+ kts indicated primarily to keep cyl head temps where I like them, but of course it keeps oil temps low too. If anything I have an issue getting the oil warm enough, it’s never beyond the half way point on the gauge, but then I won’t let me cyl head temps get very high either. This was cruise the other day at 60% power or so LOP. It was cooler than average being Dec, but it was also in Central Fl and 4,500 so it’s not real cold.

 

Actually yes, I think my oil turn black pretty quick. How should I fix things like stuck rings?

[TaildraggerPilot]

I agree with Mark about the RTV. I think somebody went a bit overboard with sealing that contact area and probably did more harm than good. 

[AaronJr]

10 minutes ago, markgrue said:

First thing that comes to mind is the rtv on the oil cooler.   The air is supposed to circulate around the ends of the oil cooler through the fins there.  I personally prefer the 15-50 oil as it is a semi synthetic oil and I feel it lubricates better than the straight weight oils.  Just my opinion and it is worth just what you paid for it. 

 

Mark 

RTV there just to fill the gaps, it forces the air to flow through middle than escaping from the side

[AaronJr]

3 minutes ago, TaildraggerPilot said:

I agree with Mark about the RTV. I think somebody went a bit overboard with sealing that contact area and probably did more harm than good. 

I’m little bit confused now, without the RTV on both sides, there are two big gaps in between, isn’t the high pressure air will just escape from the gaps and not flow through the oil cooler? 

[TaildraggerPilot]

6 minutes ago, AaronJr said:

I’m little bit confused now, without the RTV on both sides, there are two big gaps in between, isn’t the high pressure air will just escape from the gaps and not flow through the oil cooler? 

I don’t normally see any RTV on that area with the other rear-mount oil coolers I’ve seen. Any “blow-by” air would help cool the end tanks of the oil cooler anyway, right?

Edited December 24, 2024 by TaildraggerPilot
Clarity

[AaronJr]

3 minutes ago, TaildraggerPilot said:

I don’t normally see any RTV on that area with the other rear-mount oil coolers I’ve seen. 

Do you have similar setup? Any pics you can share with?

[TaildraggerPilot]

14 minutes ago, AaronJr said:

Do you have similar setup? Any pics you can share with?

My E has the trusty Dog House, and a very tightly sealed one at that. No comparison there unfortunately. A lot of Mooney drivers run around with oil temps pushing 225 and don’t even blink. I don’t make note of anything over 215 in climb or 195 in cruise, but higher temperatures than those are well within documented limits. Lycoming operating limits have been crafted over decades of development. Trust the numbers. 
Here’s a few panel data pics from a Dog House ‘67 E if anyone is interested (note: 11.5k shot was on 100 Dino oil at the tail end of a jug break-in period and the lower altitudes were later on after servicing the engine with 20W50 AW)

 

 

[AaronJr]

4 minutes ago, TaildraggerPilot said:

My E has the trusty Dog House, and a very tightly sealed one at that. No comparison there unfortunately. A lot of Mooney drivers run around with oil temps pushing 225 and don’t even blink. I don’t make note of anything over 215 in climb or 195 in cruise, but higher temperatures than those are well within documented limits. Lycoming operating limits have been crafted over decades of development. Trust the numbers. 
Here’s a few panel data pics from a Dog House ‘67 E if anyone is interested (note: 11.5k shot was on 100 Dino oil at the tail end of a jug break-in period and the lower altitudes were later on after servicing the engine with 20W50 AW)

 

 

nice panel btw!

Do you mean the area I circled in red is needed some airflow?

[TaildraggerPilot]

31 minutes ago, AaronJr said:

nice panel btw!

Do you mean the area I circled in red is needed some airflow?

Yes, that’s the RTV in question 

[PT20J]

37 minutes ago, AaronJr said:

nice panel btw!

Do you mean the area I circled in red is needed some airflow?

The circled area doesn’t need airflow. Mooney sealed the gap on the M20J with a foam rubber strip (14 in the drawing). The RTV is a sloppy way to seal the gap and makes a mess, but shouldn’t cause a problem unless so much was used that it got into the cooling fins. You can check by looking through the baffle at the back of cylinder 4.

 

[AaronJr]

3 minutes ago, PT20J said:

The circled area doesn’t need airflow. Mooney sealed the gap on the M20J with a foam rubber strip (14 in the drawing). The RTV is a sloppy way to seal the gap and makes a mess, but shouldn’t cause a problem unless so much was used that it got into the cooling fins. You can check by looking through the baffle at the back of cylinder 4.

 

Thank you, the fins is clear of rtv

[A64Pilot]

Ref oil temp, Lycoming published maximums and what Lycoming recommends. Think of it like that 500F Cyl head max temp, sure they say you can, but in several other pubs they recommend 400F max for engine longevity

This from last years IA renewal. This is what they recommend, sure higher is allowed, but not recommended.

As far as what to do about blow-by and possible stuck rings, Mike Bush has a ring flush procedure that I’m not a fan of, but several are.

Every case of stuck rings I have seen shows up in low compressions, sometimes not stupid low, but definitely a number that has me researching why.

In my cases it has resulted in cylinder removal, I’ve even disassembled everything freeing up the rings etc and putting things back together, but didn’t seem to fix the problem (My C-85) and will result in cylinder removal and an IRAN or maybe overhaul depending on what the shop suggests.

Just have to get a round tuit.

Oh, and on edit, rings wise listening for leaks at the oil fill tube or blow-by tube is more important I think than the actual compression number, obviously if there is a loud hiss from the exhaust but not the crankcase, then it’s likely your low compression is not from rings,but the exh valve.

 

Edited December 24, 2024 by A64Pilot

[takair]

How do the cylinder baffles look?  While your temps are not high, they are also not low.  Your oil temp can be slightly elevated as a result.  Also, don’t forget the baffle seals on the front of the engine to the cowl.  Those are neglected and cause some air to go under the engine.  The result is less differential pressure, less flow, higher temps.  These changes can happen with the flip of a baffle seal.

The blow by can be the result of various ring anomalies….but I would try to eliminate all of the easy stuff first.  There are a few threads, some recent, on evaluating baffle seals with flashlights, etc.

[markgrue]

On 12/24/2024 at 10:00 AM, PT20J said:

The circled area doesn’t need airflow. Mooney sealed the gap on the M20J with a foam rubber strip (14 in the drawing). The RTV is a sloppy way to seal the gap and makes a mess, but shouldn’t cause a problem unless so much was used that it got into the cooling fins. You can check by looking through the baffle at the back of cylinder 4.

 

This is how it is supposed to be.   That seal rides on top of the end Tank fins.  It allows air to flow over the end tanks.

[PT20J]

2 hours ago, markgrue said:

This is how it is supposed to be.   That seal rides on top of the end Tank fins.  It allows air to flow over the end tanks.

I can't really make out your picture. It kind of looks like the seal is on the wrong side of the flange. But regardless, the general idea is that air is supposed to flow through the oil cooler, not around it.

[1967 427]

I suspect that the vernatherm is headed south.  They don’t always open correctly when they start to fail.

[markgrue]

15 hours ago, PT20J said:

I can't really make out your picture. It kind of looks like the seal is on the wrong side of the flange. But regardless, the general idea is that air is supposed to flow through the oil cooler, not around it.

It is actually supposed to do both.  Whatever works for you.