Oil Temp - data points and questions

Hello all,

I'm looking for some opinions and perhaps suggestions that I haven't thought of yet. I've read all of the threads on here (and the RV list) about temperatures and cooling.

I have 31 hours on my RV-8. It has a 180 HP Mattituck TMX-IO360 with dual P-mags. I have replaced the vernatherm, and I have replaced the Vans-supplied Niagra 20002A with a Stewart Warner 8406R. I have cut the cowling exit so it is about 1" in front of the firewall. The baffles are sealed up tight, and the inlet ramps are glassed in on the ends.

Here is some sample data from the other day:

Takeoff with a direct climb to 8500 MSL at 115 kts IAS. OAT 70F at takeoff, decreasing to 55F at altitude.
Oil temp peaked at 218F in the climb, CHTs peaked at 370F.

At 8500 MSL, I flew for an hour like this:

Then I decended to 7500 MSL and flew for an hour like this:
My oil temp is manageable right now, but it won't be next summer if nothing changes. So far I've flown with ambient air temperatures ranging from 45F-80F, and the oil temp seems to vary more closely with CHTs than the air temperature. I never get CHTs over 400F and they usually peak at 370-380F, so I don't think I have an airflow problem related to the baffles.

So... Here are my thoughts (in order of preference based on ease of the solution):

1. Do nothing until the engine gets more time on it and see what happens.
2. Cut another few inches off the cowl exit so it's 3" in front of the firewall.
3. Put some louvers in the sides of the cowling.
4. Get a bigger oil cooler.. A friend flying a similarly-configured RV-8A has a Niagra cooler that is an inch wider than my SW, and he's never seen a temperature over 200F at any time. This would require rebuilding the back baffles, though.

Have I missed anything?

Thanks.
-Geoff

Seems like an obvious suggestion, but have you tried swapping out your oil temp probe? Maybe it's just a bad probe?

Also I would pull the oil cooler lines and make sure there are no obstructions in there. You never know.

oil temps

I have been going thru the same ****......

1st you need to call the manf. and find out what the min and max are.

The problem is most likely a baffeling problem. Make sure all the baffling is correct.

I also changed the vernatherm valve.

If it were me, I'd first choose option #1:

1. Do nothing until the engine gets more time on it and see what happens

...and wait for the warmer weather so you know what you will really get during the summer.

Just checking, but you did use -8 hose, right? I sometimes see folks (particularly with 320's) using the smaller -6 hose. That can reduce flow thru the cooler. You more than likely did use a -8 hose, but had to ask just in case. Anyway, your temps do seem marginally high and it is probably worth checking gauge calibration too.

Rather than speculate, I can just tell you that I have the same basic engine TMX-IO-360, but Slicks (should not make a difference) and although I don't have all the temp data in front of me here's some anecdotal info FWIW...

I have a 10599R Stewart Warner Oil Cooler which IIRC is the next size up from yours. I now have a Vans oil cooler shutter mounted behind the cooler to warm up the oil more in the winters because it is too cold otherwise. Yes, I know, a nice problem to have and an easy one to solve with very little effort and that was exactly what I intended. After reading the many oil cooler woes and experimenting, I got lazy, pulled out the checkbook and went for the biggest SW that I thought would be reasonable. I have the usual Vans gauge and sender.

Running close to your cruise settings: 2,350RPM and 22.0MAP - here's what I normally see:

Without the shutter, I was seeing temps of 160F during the coldest winter days (20's) and 185F on the hottest summer days (90-100). At most without the shutter I would hit 200F in a climb. Too cool in winter for sure.

Now with the shutter, I can close it down to be at 180F in the winter. The shutter fully open in the summer, the most I see is generally 190, or 220 after an agressive climb, then it settles back down to 190. At cruise during the summer, I rarely ever have it go above 195 even at higher power settings. As you can see the shutter does restrict quite a bit - even when fully open.

I will say that with the shutter now in place it is more tempermental for slow flight and I have seen it hit 240F under extreme circumstances - i.e. low and slow for a long time with some flaps down coming into SnF.

IMHO, the larger cooler is the only way to go for the -8. Although possible, I doubt you have any real baffling issues and I certainly wouldn't go cutting more off of the lower cowl just yet.

Here's where I think your problem really lies....
OK, so I lied, I am speculating now... Many folks don't realize that while the -8 isn't as tight as the -4 cowling that it is also not as big as a -6/7/9 and that means that for a baffle mounted oil cooler you can't move it up as high on the baffle to get better airflow to the cooler. There just isn't enough baffle there. At the highest point you can get it, much of the cooler is still buried behind the hot cylinder/head fins. Your cooler is probably just fine on any of the side by side RV's, but in the -8 or a -4 it probably doesn't work quite as well unless it were firewall mounted.

Just my opinion and I'm sure I will get flamed, but frankly I didn't want to waste my time on a topic that causes so much frustration and consternation among builders, so I went big, expensive and opted for over-cooling and restricting it down as needed.

If I had to do it over again, I would do the exact same thing except I would go back to my original plan to mount the cooler on the firewall if I could find a spot that I actually liked.

Good luck,

Rob

Normal

New engines run hot. Why? Some think its because its tight, there is more friction? May be but the real reason, new pistons and cylinders are not coated with carbon.

The Carbon coating acts like a ceramic coating, a thermal barrier. You have more heat being absorbed in the head where the highest oil temp are. The oil in the exhaust valve guide area is the hottest, about 20F hotter than what you read at oil inlet. Temps will go down as you break-in your engine, or season it. Good Luck.

210F is a little hot but normal and well with in limits. The never exceed oil temp is 240F. You don't want to ever get that hot but that's the limit. I like 180-200F. 220F still in the normal top of green. Ideal is about 190F. You don't want to operate at less than 130F.

PS how is your cooler mounted. Is it baffle mounted behind #4 or is it 3" dia scat feed on the firewall. 3" scat is too small to feed the cooler. You need about 3.5" dia scat, 4" dia is better but hard to fit.

N908RV said:

Just checking, but you did use -8 hose, right?

Many folks don't realize that while the -8 isn't as tight as the -4 cowling that it is also not as big as a -6/7/9 and that means that for a baffle mounted oil cooler you can't move it up as high on the baffle to get better airflow to the cooler. There just isn't enough baffle there. At the highest point you can get it, much of the cooler is still buried behind the hot cylinder/head fins. Your cooler is probably just fine on any of the side by side RV's, but in the -8 or a -4 it probably doesn't work quite as well unless it were firewall mounted.

Click to expand...

Interesting observations on oil line sizes and cowls. Personally I like the remote mount the cooler to isolate the cooler from vibration and save baffle cracking. The cooler with oil in it and oil hoses hanging off the cooler with oil in the hoses is heavy. The engine vibrates a lot. Per my comment above the Van 3" scat is on the small side for 180HP engines and totally inadequate for 200HP engines. Also you don't have to mount the cooler on the firewall necessary. You can mount it off the engine mount. The cooler exit needs to be in a low pressure area or shielded to promote flow through it.

oil temps

if I were u I would check with the manuf for the acceptable range.

220* above is un acceptable

The range is most likely going to be 175-210.

N908RV said:

Just checking, but you did use -8 hose, right? I sometimes see folks (particularly with 320's) using the smaller -6 hose. That can reduce flow thru the cooler. You more than likely did use a -8 hose, but had to ask just in case. Anyway, your temps do seem marginally high and it is probably worth checking gauge calibration too.

Click to expand...

Yeah, it's -8 hose.

I have a 10599R Stewart Warner Oil Cooler which IIRC is the next size up from yours. I now have a Vans oil cooler shutter mounted behind the cooler to warm up the oil more in the winters because it is too cold otherwise. Yes, I know, a nice problem to have and an easy one to solve with very little effort and that was exactly what I intended. After reading the many oil cooler woes and experimenting, I got lazy, pulled out the checkbook and went for the biggest SW that I thought would be reasonable. I have the usual Vans gauge and sender.

Click to expand...

My friend with the RV-8A has the Niagra version of the SW 10599R, and his temps are in line with yours. IMHO, the two extra rows in the larger cooler seems to be the key. I would have ordered the bigger cooler if I knew what the heck I was doing, but I just ordered Vans FWF kit and installed what came with it. Incidentally, my friend did exactly the same thing I did, but Vans mistakenly sent him the 9-row cooler (and larger baffle doubler) instead of the 7-row cooler, and he installed it. Lucky him.

OK, so I lied, I am speculating now... Many folks don't realize that while the -8 isn't as tight as the -4 cowling that it is also not as big as a -6/7/9 and that means that for a baffle mounted oil cooler you can't move it up as high on the baffle to get better airflow to the cooler. There just isn't enough baffle there. At the highest point you can get it, much of the cooler is still buried behind the hot cylinder/head fins. Your cooler is probably just fine on any of the side by side RV's, but in the -8 or a -4 it probably doesn't work quite as well unless it were firewall mounted.

Click to expand...

I agree with you 100%. Half of my cooler is covered by the cylinder. On the side-by-side planes, it seems to be about a third or less.

Thanks for the input and data points... Replacing the small Niagra (20002A) with the small SW (8406R) got me 15-20 degrees, but I'd still like to get another 15-20.

-Geoff

gmcjetpilot said:

210F is a little hot but normal and well with in limits. The never exceed oil temp is 240F. You don't want to ever get that hot but that's the limit. I like 180-200F. 220F still in the normal top of green. Ideal is about 190F. You don't want to operate at less than 130F.

Click to expand...

Roger all that. It's manageable now, but it won't be if I take it someplace hot next summer.

PS how is your cooler mounted. Is it baffle mounted behind #4 or is it 3" dia scat feed on the firewall. 3" scat is too small to feed the cooler. You need about 3.5" dia scat, 4" dia is better but hard to fit.

Click to expand...

Baffle behind #4. But as we've discussed in other threads, the slope of the cowl on the RV-8 prevents mounting the cooler as high as on the side-by-side planes, so at least half of it is covered by the cylinder.

-Geoff