I understand your system and it seems like sound reasoning. The reason I believe many of the Rotary builders run higher pressure is the rotary does stress the cooling system more than the Subaru. The extra BOILOVER protection rather than the simplicity of the system wins out. Not that your system wouldn't work on a rotary. The builder would just have to be sure to provide more radiator area to be sure the reduction in boilover protection (provided by higher coolant pressure) wasn't that big a factor. I'm sure you could and will make the arguement that the radiator area should be sized as such, and I wouldn't argue, but often people don't consider how much radiator is needed until they have painted themselves into a corner.
There's one coolant design that's substantially better than the others. I discovered it when doing severe ground testing...deliberately overheating my engine.
Three basic requirements:
1) Place your radiator cap and reservoir above engine. The higher the better. This allows trapped air in system to rise out of the flow and stay there.
2) Put a 24 psi cap on the system. You can throw away your overflow stuff. Not needed.
3) Always keep around 2 cups of air under the cap. This is the key item. It brings a big safety advantage. It allows you to use coolant pressure to predict well in advance how good your system is doing. It minimizes pressure. Mine never exceeds 7 psi. But if something goes wrong, then my pressure rises and I gain boilover protection due to the increase in system pressure.
If you have compression leak into the cooling system, it shows immediately as spike in pressure that reaches 24psi. But when all is normal, you never see pressure above 7 psi. If you have any cooling problem, the pressure gage will respond quicker than any other sensor.
Sounds like many of you don't have that 2 cups of air. As result, your coolant pressure regularly reaches 24 psi. Stressing components (radiator welds actually). It masks compression leaks. Makes it difficult to predict your safety margin.
Tough to explain this stuff in text, but it's a big improvement in safety margin. No downside.
To qualify the system, I omit the two cups of air. This causes pressure to rise to 24 psi. Thus proving all of my welds and connections have safety margin. Then I add the 2 cups of air and the system never rises above 7 psi unless something goes wrong....whereupon I have extra margin preventing boilover. Your biggest cooling risk as it cascades and is nearly irreversible.
On Sun, 18 Mar 2007 11:41:33 -0400 "Tracy Crook" <
lors01@msn.com> writes:
Higher coolant pressure will naturally increase the risk of a leak due to blown hose, loose clamp, radiator tank failure, etc. As in many of these matters, it is the builders choice as to which potential problem is most important.
BTW, I do recommend doing a system pressure test at annual inspection time or after making any changes. I intentionally over-pressure the system by 50% by hooking a regulated air pressure source to the overflow port on the cap fitting.
I could be wrong but the likelihood of a blown rotor housing coolant seal from coolant pressure is very low. If coolant pressure causes them to leak there was a problem that needed to be addressed long before the leak happened. Most coolant seal leaks happen at the inner seal which normally have to seal combustion chamber pressure. Even 30 psi coolant pressure is a very tiny fraction of that.
Tracy (still waiting on Bluemountain)
----- Original Message -----
Sent: Sunday, March 18, 2007 8:21 AM
Subject: [FlyRotary] Re: water boiling point
My same thought, the higher pressure the better chance of leaks, for the last 1400 hrs I have been running a 7 lb cap with no problem, I normally run about 180 for water temp but do see 220 on a hard climb out on a hot day and when at high altitude its usually so cold outside that cooling is not an issue.
Ken Welter
Thanks for your reply Tracy!
I did a google search on water boiling point. Coolant should be higher,
but it seems that water boils at 183 degrees at 16,000 feet. But that
is with no added pressure. I could not find the corrected number for the 12 psi cap.
I wonder how many blown rotor housing seals are due to higher coolant pressure ?
George Graham
Sarasota Florida
Mazda RX7 EZ
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