Over heating on Rotax 670

[959 11]

I have been fighting a over heating problem on my 670 install.

New engine from Rotax Rick.

Everything from Rick is new or re-built.

Just had installed new thermostat.

Engine temp go's to 200 degrees at 6200 rps at climb out.

Have to idle back to 3500 to get the temp back to 180 degrees.

On the ground using a laser temp gun there seems to be a hot spot around the thermostat.

EGT doesn't go over 800 degrees.

If it was timing or jetting the egt's would be higher.

Timing is spot on according to the A-P mechanic.

I'm getting fed up with this install.

It looks like I'll have to buy $1100 radiators.

Rick has sent some pics of a large radiator that should work.

Not sure where it would be mounted.

Any advice would be a help.

Thx Marv

[959 11]

Pic of radiator

[SuberAvid 617]

You might be blocking a lot of the exit opening out of the bottom of the cowling and also looks like you had to remove the lip that creates the low pressure area.  You may have to open it up more and add another lip.

[wolves200 31]

quick question here Marv: are you using a spinner? if you do, fly without it, and check back with the temps!! let me explain a little, I saw a guy airflow analysis, and he had more or less same cooling setup as you; there was a flow caused by the spinner and it acted as screen preventing the air flowing into the vents, pretty much like yours...I can see you are routing one of the hoses very close to the "Y" exhaust, you know that particular piece is extremely hot.

 

this is a very high end  performance engine, I strongly suggest go by the belly installation, save head aches and very flexible with radiators shapes.. meaning less money,  you can basically use whatever radiator you can find. 

 

 

hope this helps; very nice installation by the way!

Regards

Dimi3

Edited 30 Jun 2014 by Wolverine

[959 11]

Thx for the reply.

No to the spinner.

Was trying to keep the install clean,thats why I didn't want to go to a belly mount.

[Av8r3400 1178]

As randy said, the opening and the lip on the exhaust side of the cowling is as critical, if not more than the inlet openings.

I remember reading somewhere you are looking for an opening area with a 2:1 ratio of exhaust to inlet. The lip shape and size allows this opening to be smaller by generating aerodynamic flow while in motion.

By the look of your cowl from the above photo, your muffler blocks much of the opening and the lip is completely gone.

Having a spinner on an Avid "cheek" cowl aids flow into the inlets, too.

Edited 30 Jun 2014 by Av8r3400

[1avidflyer 1983]

One other idea to look at besides the bottom opening and lip, is to make sure the radiators are sealed off against the cowl.  Otherwise the air will try to go around the radiator instead of going through it.  If the radiators aren't sealed off a 582 will often run toward the warm side.  Using more water in your coolant mix is a help also.  Up to 90 % water and 10% antifreeze if freezing isn't an issue.  Jim Chuk 

[EDMO 1078]

This can't possibly apply to cheek rads - But in all my reading of airflow thru rads, the books say that you need a large plenum chamber to slow down the air before it goes thru the rad, and the rad edges need to be sealed so the air cannot bypass it.

   I agree on the comments about the exit port, although I have read a larger ratio, like 3 or 5 to 1. 

EdMO

[ChrisBolkan 130]

This might be a stretch but you have incredibly low EGT's.

 

That can indicate either a too rich condition, or too much load. if you are in a too much load condition, you might be able to pull the pitch back a bit, bring the EGT's up where they belong, and in doing so produce less heat because the engine won't be working so hard.

 

Others mentioned the cowl lip and airflow..super important.

 

Also you might consider running 10% coolant and distilled water. That might get you about 10 degrees.

[C5Engineer 1170]

I am with Chris on the low egts. An over pitched motor will create a lot of excess heat. You should be seeing 1000-1100 degrees on climbout at least. With my IVO prop I can watch the water temp go up in cruise just by bumping in some pitch. The in cowl radiators are also pretty notorious for overheating issues. As a result many have gone to belly radiators.

[BryceKat 125]

What tach are you using? Westachs are liars 😄

[Bandit 286]

Leni went from a belly radiator to the cheek radiators. It solved his cooling problems.

[959 11]

I believe the pitch is set at 12.5 degrees static to limit rpms at 6200

[C5Engineer 1170]

On a needle tachometer from the lighting coil or a digital tiny tach off a plug wire?

[959 11]

From the lightning coil

[boxwrench 2]

I agree with the airfow comments.  If you look at that big muffler sticking out the bottom of the cowling the top half is actually deflecting air up into the bottom cowling.  I would try a temorary piece of aluminum attatched to the bottom cowling to bottom of muffler and add a lip around the rest of thr bottom cowling opening.  You can put huge radiators on it but if the air does not flow through them they will still not cool the water/antifreeze.

[Av8r3400 1178]

Get a tiny tach. Your tach is wrong. Guaranteed.

[akflyer 1427]

I had cut the bottom lip off my cowling when I was using the belly radiator.  When I went to the incowl radiators like you have I had to glass that lip back on and I had to put baffles around the radiators to keep all airflow going straight through the radiators.  since I have done that I have not gotten it to break 180 in a hard extended climb.

 

I would also check that tack with an optical hobby tach on the prop (then do the math for your reduction on the gear box) or spent 45 bucks on a tiny tach,  The Analog tachs are about like the skidoo dream o meters they put in the dash on snowmachines that tell you your going 125 when in reality, on radar, you lucky to hit 95 MPH. 

 

Your ETGS are really low and will lead to carbon build up as well as over loading the engine.  I dont think your getting the RPM that you think you are.  What are your EGTS in cruise?  you really need to get them up around 1100 to help burn that carbon out.

 

What do your plugs look like?  EGTS have errors in them and are only to be trusted to show a "trend"  You plug color is the life line on a 2 stroke and should be what you judge your EGT temps against.  By that, I mean that if you are getting a nice tan colored plug with no fouling, but your EGTS are only showing 900 or 1000, then use that as you bench mark on the EGTS and keep an eye on them from there if they start showing an up or down trend to let you know something is changing in the mixture or loading of the engine.

 

What RPM are you getting on take off and climb out, and what are you hitting at straight and level wide open throttle?

 

[sioux201 84]

More power = more heat = more water/air flow, radiators work better with low pressure cowlings, not high pressure to radiators!

[allonsye 85]

Marv -

 

Did you see this through?  What was the outcome?

[959 11]

I put electrical fans 1 each on the radiators.

Just a stop gab till I get the new radiator built.

[allonsye 85]

Good, glad you're onto a permanent solution. Did you address cowl issues already as well?

 

Aside from that, what do you think of the 670?  I was chatting with Rick about it - he really loves this thing. How's it been working for you you?  I'm interested in it but have a few concerns.

 

cheers:)

[959 11]

If I was to sell the tuned pipe I would want $2000 for it.

I know this is not what you asked but that was one of the most challenging part of the project.

This is from me who build my chassis car that runs in the 8's.

 

I would do it again.

The plane is very lively.

 

Next I'm going t o put the  clutch in.

But I will buy a couple of extra clutch lining because of the extra hp.

[akflyer 1427]

I talked to the shop that developed the clutch. (twisted metal racing in canuk land) and Tony told me that a lot of guys were using them in air boats running 150+ HP on them with no issues.  I had asked him becasue I figured on using it for my 800 conversion as it will be running around 120 HP (just loafing along for that engine) and he said it should be fine and last just as long.  The secret is to not doink around in the RPM range where it throws the pucks out ( dont play around with the throttle around the 2500 RPM range, just get the prop swinging then keep the RPM up to keep it fully engaged.  I love the clutch and I hate every start up and shut down I have been doing without it this summer.  It will be getting put back on when I get home this trip I hope.

 

[LORENZ 9]

Did the new radiators help?

 

Did you check to see that your not over proping the 670?

 

My 670 is Being built and I really hope I don't have over heating issues. Im buying the exhaust parts and cones from Mike, the guy who builds the exhausts for Rotax Rick, and I will be assembling and welding them up myself. This will keep the "tune" that Mike and Rick have worked so hard to produceon the dyno and have thw 670 jetted for , while giving me a couple inches either way to get her fit into the MKIV Cowel... Wish me luck.