First of all I really appreciate the knowledge base here and the help everyone has given me. New to this awesome sport/pastime. That said this weekend was a couple of days spent on my Scarab 29 and at almost every RPM range I have one motor running at about 170 degrees and one running 145 degrees. (Puget sound so the water is pretty cold) I also notice there is a pretty big spread in raw water pressure. Is this a sign of a failing water impeller? also the motor running the warmest get a sulfur smell after prolonged running. Thoughts? Thank you

if the warmer engine has lower water pressure I would think the pump is about finished.

What motors? If they are EFI/MPI, 170 sounds normal. If they are carb motors 170 is too warm.

They are 350 Mag MPI and I also think the 170 is normal. The cooler motor has the lower water pressure reading. Which I just can not explain unless the guages are cross wired.

Maby the gauge is not reading the right temp. One of mine was reading a little over 180,but the real temperature was 170.

When was the last time the impellors were changed? If the boat is new to you and you are not sure, that's the first thing I would do. I would back flush all the cooling lines too. See where you are after that. Gauges don't seem to go bad nearly as frequently as the senders. The senders is the next place I would look if the impellors are new.

Backflushing didn't do jack for me. The pieces of old impeller were so jammed into the oil cooler I had to pluck them out with needle nose pliers.

Pull the hose off the oil cooler inlet and outlet after running the boat for a while, the heat will make the hoses easier to remove. Use a flashlight to shine upward through the cooler, and a coat hanger or welding rod to mechanically sweep every tube clean.