so i took the new boat out for the first time this weekend. a few lil issues. its is a 30' scarab with twin 350 chevy with vortec heads, crane cams and roller rockers.

1. on both engines water temp goes up and down from 200-150. it has crossovers with bypasses and 160 thermostats. im guessing i need 140 thermostats with a couple 3/16 holes drilled. sound about right?

2. i can only get the boat up about 48mph. the most rpms im gettin are 4000. what rpms should these motors be turning? the engines only have like 20 hours on them. the props are 21p. i was told the boat use to go 65mph? all speeds are gps speeds.

any help would be great!!

thanks scott

With twin 330's in good condition, that boat will run 62mph. With small blocks in good condition I would guess 58-60. Your rpms are way low. Try a pair of 19's. Your rpms should be in the 5000-5500 range.

I agree, and i would take the thermostats out and just take it easy untill u see the temp neddle move !

Replace sparkplugs and go at it again,,you may have a fouled plug from engine foging..


engine temps, make sure your thermostat housing's have the proper gaskets with the brass rivets in them..also if the sensor is in the back of the intake manifold it will show 200*...move them to the front of the engine..

the temp sensors are in the front of the engine. i will hopefully do some more testing this weekend . thanks for all the help. any more advice let me know

thanks scott

My boat has a single 350 and at wot runs 4400 at just over 160 F at about 60 with just me in the boat(22 ft. scarab excel) IS that normal temp for my boat?

another thing to add...im getting a little white smoke out of the left bank on both engines when idleing in the channel? not sure what thats about?

Smoke or Steam? Have someone smell it.. Might be nothing Black is poor fuel burn, blue is oil, white however is due to antifreeze burn so it may be steam you are seeing, or oil burn that looks white but you can smell it if that is the case.
Pull your plugs for sure, it will give you an indication easily.

i would do a compression check on both engines,if thats ok,next would be plugs,cap,rotor&wires,also,check total ignition timing.never hurts to replace fuel filters while your at it.