Okay guys, here's a doozie I really need help with...
Once apon a time, I wanted to get my Pilot back up and running after my lower back fiasco, so I decided to get a couple of things fixed and some maintenance done. I had a problem with my reserve fuel sensor, which wasn't working, and another problem with leaking coolant, so I figured I'd tackle these problems head-on.
Regarding the reserve fuel sensor, I ordered a replacement sensor. No big deal.
Regarding the leaking coolant, I looked under the Pilot with the engine cranked and saw that I had a shot mechanical seal (leaking coolant profusely through the cheater hole under the water pump) which, I believe, was caused by a kinked radiator hose that was going to the head. The hose used to curve nicely into the top of the head, but with time, it developed a kink which I believe caused the coolant to stop flowing, which, in turn, caused the mechanical seal to overheat and crack in two places. Since I was changing hoses and getting deep into the whole cooling system, I decided to change out the radiator cap, too. It was looking rather ragged after all of these years of use.
The rebuild began with the removal of the fuel tank. Not only was the reserve fuel sensor shot, but I noticed that there was a small amount of surface rust inside the fuel tank. I took some washers and dumped them into the fuel tank, along with some POR-15 metal ready conditioner in order to remedy the surface rust situation. The tank came out great, so I changed out the bad sensor for the good one and completed the task at hand.
Next, I had to tackle the right side cover in order to change out the mechanical seal. Not only did I change out the mechanical seal, but I put a new water pump shaft in as well. Call it preventative maintenance or whatever you like, but it helps me sleep at night.
Either way, I put everything back together and decided to do some maintenance work. Not only did the right side get new oil, but the case got an oil change as well.
Here I was, all done with everything I set out to do, but things didn't work out as good as I had hoped. On the maiden voyage out, my engine quit 30 feet from the house. Fortunately, the culprit was a defective spark plug and a new one cured the illness.
Next, since I had cleaned out the tank, the two subsequent fuel tank flushes apparently weren't enough. A few little (and I mean little) rust particles were enough to cause my carburetor's overflow tubes to go into fuel overflow during my second test run. Fortunately, a thorough cleaning of my carburetor's float bowl was all she needed to squash that issue.
Lastly, this is the problem I need help with. I fill the radiator with coolant to the top, purge the air by throttling the engine, then top off with coolant again. If I take her out for a hard run, she'll start to overheat only a few minutes into the run. When the Digatron yells at me, I shut her down and take a peek into the radiator. By this time, it's usually half empty. The only leak point is the pressure relief hole built in to the radiator cap. This is only supposed to spew when the cooling system reaches 20psi. To test this, I put a gauge onto the small radiator hose that used to carry coolant through the OEM carburetor's heating system. I pressurize the system to 15psi without any leakage of pressure. As soon as I hit 20psi, the pressure relief hole in the cap does what it's supposed to do and spews coolant.
After the repair of the mechanical seal, I have a beautiful stream of coolant flowing through the cooling system. If you peek into the neck of the radiator, you can see the coolant flow coming back in from the head's return hose.
After the pressure test, I have concluded that I don't have any leaks in the cooling system. I have also concluded that the radiator cap is working as per the manual's specifications.
I have checked and rechecked all the hoses and can certify that there are no hoses that are kinked or pinched in any way.
I have flushed the radiator with a garden hose from the top to the bottom and I don't have any obstructions in the radiator.
I have flushed the entire cooling system via the bottom radiator hose with the garden hose, causing fresh water to flow through the entire cooling system (minus the radiator) and it comes through successfully, which indicates that there are no obstructions in the cooling system.
Why, then, when my engine heats up during a hard ride, does the pressure of the water exceed 20psi and cause the radiator cap to go into "pressure protection mode" and spew coolant not only into the reserve tank, but out through the cap's hole?
Has anyone ever encountered this problem and what do I do to remedy the problem?
Can anyone think of something that I haven't tried yet?
As you might imagine, this one is really kicking my ass!
Thank you in advance for your help!!!