Expert: Jeff Grigg - 2/18/2008

Question
QUESTION: How can I tell if the poppet valve is working prpoerly on my 1996 Mariner?

ANSWER: It is a little difficult. If it is leaking out the weep hole the diaphragm is bad. If the water pump is in good shape and the thermostats are working as they should, but the engine is too hot at cruise or above, but seems to run properly at slow speeds the poppit valve may not be opening correctly. On a 12 year old engine if you are just not sure, go ahead and replace it with a new kit. It isn't that expensive and can be done in less than an hour.
Jeff

---------- FOLLOW-UP ----------

QUESTION: Thanks for the answer on the poppet valve.The water line from the poppet to the top of the engine should that have water pressure all the time or just when the poppet operates? Could you explain how the poppet system works or send me a canned explanation? Thanks again for the great service.
Paul

Answer
There should be some water all the time depending on the year of the engine. Basically it works like this, as you increase the speed and load on an engine it needs increased cooling water from low speeds and idle. As the engine goes through the water the faster you go the more water pressure into the intakes of the lower unit, through the water pump and into the engine. This pushes the poppit valve off of it's seat and allows increased cooling into the engine. As you slow down the pressure decreases and the spring loaded poppit re-seats cutting off the increased water flow.
Jeff