Hot running 2.5 engine

dunc

RAF/Sparrowhawk/SC 2.5 FI
It's not even summer yet. As I transitioned from learning to fly gyro in the pattern, to short (<50 mile) x-country flights, in my newly purchased used RAF 2000, I noticed that the coolant temperature would run at the 225 redline, and easily approach 250 over longer distances at 4800 RPM, 70 mph cruise. I originally removed and placed the sensor in some boiling water, or about 200 F at this altitude (digitally measured) and saw the RAF gauge measuring 225 F. I figured the sensor was bad, and continued flying assuming indicate 225 was "really" 200 so "no problem".

I bought another sensor and just now replaced the old one. Same in flight measurements were seen. I returned to testing with a pan of boiling water, but this time found the gauge was properly measuring the 200 boiling temp. Both sensors measure about 50 ohms at 200 F, but I can't find what their spec is. I think I was using a battery charger during my earlier test so the battery voltage may have been higher, causing an error in the earlier meter reading of boiling water. In flight my battery voltage is about 13.3 - 13.5 volts.

So I now think I have real problem, not an instrument accuracy problem. I burped the system by squeezing the radiator hoses and no longer see any bubbles raising to the overflow tank. My water pump has the vertically mounted thermostat which I understand is more prone to air issues. The cabin heater works fine. I replaced pump and stat along with oil pump, timing belt and pulleys late last year. I have a single row radiator, and at 75 F today's density altitude was about 8000 MSL, so not a "lot" of airflow. I have not flown at sea level to see if thicker air would make a difference, thus imply a thicker (more core) radiator is needed here at my 6500 MSL home.

Ideas for what next? Any way to insure or test that no air is remaining is the coolant system?
 
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Vance

Gyroplane CFI
The second to the last RAF I worked on with cooling problems took almost an hour to get all the air out of the system after we changed the thermostat.

The last RAF I worked on with cooling problems had the sensor hooked up backward.

I have seen head gasket problems with EJ25s where the oil leaks into the coolant. Overheating was intermittent.

Good luck with your cooling challenges.
 

dunc

RAF/Sparrowhawk/SC 2.5 FI
Thanks Vance. During that hour, were you simply squeezing the upper radiator hose? Was the engine running? Most Soobie car help videos show this done with the engine running - I have not tried that. Not sure how sensor can be hooked up backwards. There is just one wire, and it goes to the gauge.
 

Vance

Gyroplane CFI
Both Duncan. We could feel the bubbles in the hose. I don't even know how important it is.
 

Smack

Re-member?
On my Mini Cooper, the trick to bleeding air out of the coolant system is to put the shop vac on the reservoir spout and run the engine up to operating temperature (thermostat opening).
Pulling a vacuum helps to remove trapped air in the system. Works pretty well.
Brian
 

dunc

RAF/Sparrowhawk/SC 2.5 FI
Smack - what would keep the coolant system filled? I am certain my shop vac would suck it dry in short order. Most of the YouTube "help" videos, etc. use a funnel on the radiator top and just keep it filled while squeezing the upper radiator hose. I think the RAF overflow tank will do that same job if the cap is removed.

Vance, I will try burping while engine is running. It may have something to do with coolant flow to dislodge the air bubbles. One video showed drilling additional bypass holes in the thermostat. The guy was using a drill press, and did not secure the thermostat. You can imagine what happened as the thermostat came loose from his grip and whirred about the drill. Luckily it did not come off.
 

AirCommandPilot

Just a fledgeling
I agree with taking your thermostat out and drill a few 1/8" holes in the plate. This will allow the trapped air past the thermostat even if it hasn't opened. Also, make sure your "burping" it from the highest point in the system that is on the water outlet side. On my EA82 I had to make a "tall tube" with a radiator cap on the water pump outlet tube to burp the air. I tried burping it from the expansion tank, but it would not.Riser.gif
 

Eric S

Junior Member
Duncan,

Yes, burp it with the engine running including after each flight for a while. That worked for me. I was surprised how long air kept coming out.
 

Smack

Re-member?
Dunc, pulling a vacuum WITHOUT flow is only reducing the pressure, NO FLOW of liquid. Seal the vacuum hose against the reservoir so that it does not suck air in.

Similar to opening the top of a beer or carbonated beverage; the pressure (in the can) is reduced and the dissolved CO2 comes out of solution due to that pressure reduction.
 

dunc

RAF/Sparrowhawk/SC 2.5 FI
I agree with taking your thermostat out and drill a few 1/8" holes in the plate. This will allow the trapped air past the thermostat even if it hasn't opened. Also, make sure your "burping" it from the highest point in the system that is on the water outlet side. On my EA82 I had to make a "tall tube" with a radiator cap on the water pump outlet tube to burp the air. I tried burping it from the expansion tank, but it would not.View attachment 1144616
I don't understand this. The water pump draws cooled coolant from the bottom of the radiator, and forces INTO the engine, assuming the thermostat has opened. Thus the pump "outlet" is directly into the engine block. Of course I am speaking about a L25, not an EA82 of which I confess to know nothing. My fill cap is already highest point in system, not counting the overflow reservoir.
 

dunc

RAF/Sparrowhawk/SC 2.5 FI
OAT is 79 degrees and after tying down gyro and achieving 200+ F on the coolant gauge, I then tried burping the hot (top) radiator hose while engine running at about 1600 RPM. No air bubbles seen running up the overflow into the reservoir. I note that the upper hose is quite hot, and the upper tank portion of radiator is about 150 F, while the lower portion is about 90 F and the return hose is quite cool. Both heater hoses are hot. There is a rapid change in radiator temperature (very top is 150 while just below, e.g. the tubes are about 90). Does this really mean no coolant is flowing past the thermostat?

After shut down, to avoid possible prop danger, a quick laser temp check of the temp sensor center connector shows 145-158 F with the gauge showing about 195. Note the system voltage is only about 12.5 V at this time, so the gauge reading is low. I have proven to myself the temp sensor and gauge are accurate, at least at 200 F and the nominal 13.3 V seen when charging during flight. It is similar checks that made me originally believe that gauge was reading low, but not any more.

20190608_171118.jpg
 

Kolibri

FW and Gyros
OAT is 79 degrees and after tying down gyro and achieving 200+ F on the coolant gauge
Most thermostats open up at, what?, 170° or 180°. Have you ever replaced yours?

Do you have an engine oil temp gauge?
That'd be more illuminating.

What oil viscosity are you using? 5W-30 makes sense to me at your altitude.
If you're using any -40 weight, your engine may be working harder than necessary.

Regards,
Kolibri
 

dunc

RAF/Sparrowhawk/SC 2.5 FI
My like new thermostat is rated at 82 C, or 180 F. I just tested on stove top. it starts opening at 88 C, and fully open at 92.

No oil temp gauge. I think the most significant evidence is

1) At 250 F on gauge, the radiator top tank measures 150 F on the top tank, and 88 F on the lower tank. Radiator should have about 10 degree temp gradient as coolant flows.

2) If running at full stable temp (225+ on gauge), and the coolant filling cap is removed, no fluid flow is seen below where the cap sits.

I think both of these mean the coolant thermostat is not opening, regardless of oil viscosity or temperature.
 
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Kolibri

FW and Gyros
Since you successfully tested it on the stove top, it should be opening. Hmmmm.
Can its opening be blocked within the housing?
 

Vance

Gyroplane CFI
My like new thermostat is rated at 82 C, or 180 F. I just tested on stove top. it starts opening at 88 C, and fully open at 92.

No oil temp gauge. I think the most significant evidence is

1) At 250 F on gauge, the radiator top tank measures 150 F on the top tank, and 88 F on the lower tank. Radiator should have about 10 degree temp gradient as coolant flows.

2) If running at full stable temp (225+ on gauge), and the coolant filling cap is removed, no fluid flow is seen below where the cap sits.

I think both of these mean the coolant thermostat is not opening, regardless of oil viscosity or temperature.
The thermostat needs to be in the water to work.

In my experience if there is air in the system the thermostat won’t open trapping the air in the system.

That is why some Subaru enthusiasts recommend drilling little holes in the thermostat to help get rid of the trapped air.

Based on your description the coolant is not circulating so either the thermostat is not opening or the water pump is not pumping.

We got the one I was working on working by burping it for an inordinate amount of time and drilling little holes in the thermostat.

We just kept at it because we could not think of anything else to try.

Once the coolant was circulating everything worked fine and the problem has not returned as far as I know.

I feel a thermostat has value or we would have just pulled it out to see if we could get the water circulating.

I am not a mechanic and this is the first and only EJ25 I had this problem with.
 

dunc

RAF/Sparrowhawk/SC 2.5 FI
I really appreciate your suggestions, fellas!

1. Thermostat operational blockage or installation error (upside down) are physically impossible.

2. The like-new coolant pump works, as witnessed by the cabin heater hoses both being hot and at same temperature.

3. I have tried two "guaranteed no air bubble" filling methods. One uses a large funnel, and slow addition of fluid, watch for thermostat opening denoted by flow observed below the filler cap. The other method uses shop air and venturi effect to make a partial vacuum, as can be seen on gauge and collapsed radiator hose, then open a valve to fill from reservoir and ensure that fill line has no air. I have attached images of these methods in use. I like the venturi method very much, and recapture some of the antifreeze from the ejecta hose.

4. I have read several Soobie threads with pros and cons about drilling the thermostat. I understand that Sparrowhawk actually suggests this resolution in their manual. Since the thermostat is out right now, I am going to try this today. They are cheap. This will be sixth time I have drained and refilled the system, the last three have used the venturi system. It is relatively clean. The number, location, and diameter of the additional holes varies based on who is telling the story. It seems more art than science! Anybody have anecdotal evidence here?

5. While system is drained, today I will also attempt a simple garden hose flow test through the radiator and its two hoses. Glad that this will be done in summer temperatures! Alternatively I can try a test with the thermostat removed. This requires fabricating a thermostat housing gasket.

6. How and when to fill the overflow reservoir remains unclear. I have a Mityvac syringe, and use a 1/4 inch wooden dowel rod for dipstick. I fill to about 4 inches below the filler. I built an adapter from PVC to use the venturi filler, and hoped the vacuum would open the radiator cap relief valve sufficiently to fill the entire system. But the filler neck is too close to the rotor mast and I can't get the first PVC elbow on.
 

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dunc

RAF/Sparrowhawk/SC 2.5 FI
I used a garden hose to check radiator and hoses - no noticeable flow decrease noted. Drilled one 3/16 hole in thermostat. Refilled coolant system using venturi vacuum method and topped off overflow tank using Mityvac. A ground run of 20 minutes at 1500 RPM showed 150 F on panel gauge, much cooler than previous tests. A hopeful 15 minute flight with two landings had panel gauge approaching 250 F - same as before. A few minutes after shut-down the panel gauge showed 225 F, the radiator upper tank exterior was 150 F, bottom was 130 F, and the engine temp sensor was 150 F using laser point thermometer. A post-flight burp yielded six 2-3 inch bubbles into overflow tubing using the upper radiator hose.

All same as before, except a longer warm up time.
 

dunc

RAF/Sparrowhawk/SC 2.5 FI
A quick request - can one of you Soobie guys with a laser thermometer check your radiator upper and lower tank temps at normal operating temperature? Let me know what you read, also at the top of temp sensor. Thanks!
 
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