Raw Water Pump

Without the t-stat, the operating temp wont't get hot enough, the engine parts won't expand the the optimum size, and so you may experince some engine damage from loose tolerances between them. Without the t stat, the engine shouldn't get much more than 110 degrees.

Operating without the t stat to trouble shoot or to get back home is fine. I wouldn't run for several hours with it out.

Put the t stat in boiling water with a theometer to ensure it isn't opening and closing at the right temp (143 or 160 depending on t stat) This could help pinpoint your problem.

The engine water pump can leak if it is worn, it is underpressure when the engine is turning.   The Raw water pump shouldn't leak, it will suck in air rather than leak out water if the seals are worn.

The pump could just be worn out, sometimes it just need repacing. I have a spare I could sell you if you are looking for one.

Hey all. My newly acquired 1968 Mustang with a Ford 289 has a sucking problem. The previous owner advised me that when first starting the engine it must be reved up to get the raw water pump to pumping OR plaining the boat will also get it pumping. He said he replaced the impeller but that did not help. Well, he is absolutly right. Am I in need of a new pump? Could the problem be a blocked line somewhere? Your help is appreciated. The engine heats up pretty fast if no water is moving though it.