Everyone I know about using the rotary plugs this bypass, and uses either a standard thermostat, or no thermostat at all for a/c use.
To be sure we're on the same page, when you say bypass, do you mean from the water pump output back to somewhere on the block, without going through the radiator? If the answer is yes, is there any chance that when the pump starts working harder at higher rpm, more of the water is taking the path of less resistance, back through the block instead of through the rad?
Do you have a diagram of your cooling setup?
From the video, it looks like a simple engine in/out, radiator in out. no overflow or bypasses. but I can't see everything from the video.
What are you using for cooling? (water, 50/50 glycol mix, Evans waterless?)
How's the radiator cap? Pressure rating? and can you check the pressure of the cooling system?
I've had weird issues when the radiator cap no longer seals properly. 1 symptom is the overflow tank will fill up and not siphon back when cooling down, but I also think the system doesn't pressurize and doesn't work quite right. If I have to remove the cap, I'll replace it with a new one.
How hot do you let it get before you shut it down?
Just a thought. (Subaru 3.0)
It may be trapped air, but your cavitation comment may be more accurate. I would suggest you install a restrictor in the two bypasses you have there. Maybe a 1/4" hole in each. Then install the thermostat.
Here is why, the pump is likely located up high relative to the overall cooling pool, yielding low suction head. Then to aggravate the issue, the pump is sized for a particular back pressure, forcing flow through the head.
Part of the systems' restriction is the thermostat and part is the two coolers. The result of lowering the system restriction is 1. allowing vastly increased flow, that thereby increases pump inlet velocity and lowering NPSH, net positive suction head. This can create cavitation and . . 2. excessive bypass lowers the pressure, and therefore velocity across the head/block, which would aggravate the possibility for incipient boiling.
Overall, it is likely #1 is the major part of your issue as the power is not high enough to have the #2 issue.
After getting the flows right, then we can see if you need some vapor bleed lines. Bleed lines are not unusual for highly loaded engines and will collect gas and direct back to the top tank.
If you have the thermostat housing open, can you take and post a picture to see where the bypass is located?
Worth what you paid for it.
3000 rpm and 20 inches is pretty low hp, similar to going up a moderate hill in a car on the highway-perhaps around 40-50hp. I've run liquid cooled engines with props at these settings and nothing gets hot with some pretty small rads at 70F ambient temps.
The 45 degree delta is something I've never seen in all my rad testing and this pretty well must be due to the water flow being low at high rpms which points to cavitation. My deltas are typically 10-20F across the rad inlet to outlet.
Maybe install a flow meter inline and see what's happening as rpms increase.
Bill's advice on the active bleed line is good. Those have proven to be highly beneficial on Subarus which can trap air easily due to their horizontal layout. I have a .125 ID hose going from the the top of my coolant crossover pipe joining the two banks to the top of my expansion tank.
To be sure we're on the same page, when you say bypass, do you mean from the water pump output back to somewhere on the block, without going through the radiator? If the answer is yes, is there any chance that when the pump starts working harder at higher rpm, more of the water is taking the path of less resistance, back through the block instead of through the rad?
Yes I had totally stock 2.5 imprezza subie, 165 hp,with SDS and 950lbs empty weight, turned out to be a rocket ship, way to much for someone my age, so in
Process building zenith 701, definitely use auto eng in it ! It went to good home
in S. America . Tom
My cooling troubles are SOLVED!
I do believe that 90% of it was just like Ross and others suggested, BUBBLES! Trapped air.
Super thankful to Ross, Bill, Andy, Jon, Jeff, RV7charlie and all who gave advice and support.
I ran it at 4800 rpm and about 28" MAP - for more than 10 minutes, which is kind of harry on a teststand in my parking lot at home.....and it held at 185*F outlet, and about 159*F inlet temp. This was with NO thermostat and the bypass open.
I will add the turbo back on and see how that goes. I have read different theories on the routing of turbo water cooling lines. These are on the sides of the turbo housing. Some say both should point up to allow water to pool to aid in cooling after shut down, some say one up and one down and some say both down.
Ross, if you are reading this, I know you have a ton of experience at this. what is yoru advice on the turbo water cooling lines. I have mine on banjo fittings. So they either have to point up or down. I have had them both pointing up and this does allow for water to "rest" in the turbo housing after shut down. But since my turbo is really up high on the block, they have a tendency to encourage air to get trapped in the top after shutdown. I can try to find a pic to show you what I mean.....
Charlie
The photo shows up fine. Lots of time spent fitting those tubes. I remember this step well on my 2 planes.
The power setting in the video is about where I run my Sube in cruise- 25 inches and 4200 rpm. The Honda sounds nice and smooth there. Keep up the good work.
My cooling troubles are SOLVED!
I will add the turbo back on and see how that goes. I have read different theories on the routing of turbo water cooling lines. These are on the sides of the turbo housing. Some say both should point up to allow water to pool to aid in cooling after shut down, some say one up and one down and some say both down.
Charlie
Most turbos have an option for a water cooled center section and they are a must when running ball bearings. My 40 years experience with journal bearing turbos is you don't need the water if you run Mobil 1 oil and don't shut the engine down with the turbine housing red hot. Let the engine run slow and idle for a minute or so as you finish your trip.
I've ice and road raced them (16 years) driven them on the street since 1978 to the tune of a million km+ and flown them for 15 years. Never had a bearing or seal failure yet with Mobil 1 in any of them.
The water lines are a liability in an aircraft IMO. More things to fail (and maybe lose your coolant), more weight, more complexity. We don't run water cooled turbos on the Reno stuff since there is no water available and that is a really severe test with EGTs up to 1800F and pushing the units right near their N1 limits.
I'll defer to your experience, Ross. Although, for validation of a good process, I might recommend a thermocouple on the housing to confirm this installation and cool down phase. Mobil 1 will tolerate much higher temps w/o coking.
Yes, the main key to not getting coking failures on the bearings and turbine end seals is the synthetic oil and that 1 minute of lower rpms and load before shutdown. Andy also runs synthetic automotive oil in his Race #30 Lancair which won Sport Class Gold this year.
I was having problems in my Audi with the turbo seals, excessive smoke, and oil consumption. Was using Mobil 1 full synthetic until an oil expert advised to not run a full-synthetic oil. Smoking and coking problems stopped immediately going to a semi-synthetic oil of the same weight. Oil consumption was reduced 90%. I was shocked because I was always under the impression synthetics were superior.
You can see most of my rad development stuff near the end of these 2 pages:
http://www.sdsefi.com/rv16.htm
http://www.sdsefi.com/rv17.htm
There are so many separate pages on our site, it's hard to build a search feature at this point. You can try the Control F command on each page to find something specific.
The cooling is so good, I leave it closed most of the time. I'll open it on the ground during a long hold or on a long climb on a hot day.
In the winter, I block off 50% of the rad with a foam insert and block off 30% of the heater core face as well. The door remains closed all time in the winter even with these things done. On final, it will still drop to 140F.
The heater core is in the thermostat loop and provides a lot of cooling. The thermostat does not have control over that water flow
Most auto engines for the last 30 years have the heater core flowing coolant all the time with no valve in the flow like the old days-they just mix hot and cold air with the heater control. This means the heater core coolant flow bypasses the thermostat all the time.
I take hot air off about 30% of the core through twin 2 inch SCAT hoses and the rest bypasses so the core offers a bit more cooling capacity for the engine at all times.
I don't use any other bypass hose in my setup for the thermostat. The heater core in plumbed with 5/8 hose.
On days below -10C, the heater core alone is sufficient to cool the engine in cruise below 25 inches. The thermostat never opens. The core is fed by a single ram duct via 3" SCAT hose and a difuser with internal guide vanes to spread the flow over the whole core face. The core is 8 X 8 X 1.625