MCI5C Cooling system

[jjrbus]

  Started a little correspondence with Gary, but do not want to hijack Musicmans thread. So will start a new one.
I have a 79 5C Saudi model It is a 6V71 with a MT644 transmission.  This bus was built for service in Saudi Arabia and is impossible to overheat.I've had it up and down mountains in AZ and CA in the summer.
The problem I have had is I cannot keep coolant in the sight glass in the expansion tank. I have been told that this is a design flaw in the system. The coolant level will be about 1 inch under the sight glass and stay there. To overcome this I replaced the hose under the tank with clear hose, which has to be replaced/cleaned once a year.
This year I decided to try to fix this. After conferring with my bus guru's. Jack Conrad/Jerry Jenkinson. We decided that the cooling system is not holding pressure. According to Detroit the system should carry 7 lbs.
The pressure regulator and the fill cap gasket seemed to be the problems. The fill cap gasket was hard as a rock, its probobly been in there 30 years!
I opted to remove the presure regulator  (1st picture) which was mounted to the expansion tank and plug the opening.
I removed and modified the filler by adding a automotive style radiator  neck and 7 lb cap. The base was no longer flat, but it was brass and rubbing it over a piece of sandpaper on a flat piece of steel quickly restored it.
While I had the system apart and becuse the bus runs so cool, I replaced the 170 degree thermostats with 180's. I might have been able to go to 190's but no use in pushing the envelope.
I have not drove much since doing this. The system now holds pressure and the coolant is staying in the sight glass. The higher tempature should result in better combustion and fuel economy.   HTH

[gumpy]

Interesting. I don't quite understand where you put that filler cap neck, though.

My bus actually has a schrader valve where you can check the pressure, though I admit I've not actually used it. I did replace the pressure valve on mine when I cleaned up my cooling system. The fill cap seals well. I guess I should check the pressure sometime, though.

Yes, you should be able to keep coolant in the window at all times. It should be about half full when cold, and should fill completely when the engine coolant is warmed up.

craig