1999 S225 OX66 Pressure Valve Questions

Well, I dug into both engines this weekend and came across something interesting. One engine had the pressure valve plunger installed backwards... actually jammed in the grommet. This generates a few questions for me:<br /> - What symptom would this cause? This engine ran "normal" for temp, ie .. no alarms.<br /> - How does the pressure valve operate? <br /> - Should I expect any engine damage from this?<br />At the same time I checked both thermostats for correct opening temp and gap. Both looked OK.

Re: 1999 S225 OX66 Pressure Valve Questions

if its stuck open it will cause overheat problems at low RPM. stuck shut maybe higher water pressure. usually they are jammed cause corrosion built up between the cover and the grommet. even installed backwards they wont jam cause its the same diameter on both ends<br /> at low speeds pump volume and pressure are reduced due to low pump speeds. as the t-stats open and close pressure must be maintained. water boils at a higher temp under pressure and high pressure water tends to fill all the voids better. but at 5000 RPM pressure may become to great so the valve is opened and allows excess water pressure to be dumped down the exhaust leg. opening pressure is controled by the spring.

Re: 1999 S225 OX66 Pressure Valve Questions

rodbolt,<br /> thanks for the description. It doesn't sound like stuck closed is a big problem. The plungers on both of these engines have a slightly larger short end, or spring side end, than the end that goes into the cooling passage. the one that was backwards was jammed in so tight I was afraid of breaking the plunger during removal. These had minimal corrosion so I guess that is a good sign.

Re: 1999 S225 OX66 Pressure Valve Questions

the valves wont corrode. the area under the grommet will and squeeze the grommet down. yes the spring side is a tad longer than the cooling side to assit in guiding the spring. but if you can see 4 tracks in the grommet its corroded under the grommet and the exhaust housing needs a thourough scraping