'78 bayliner monterey24' 350/260 runs hot

[RandyJ]

I don't know how hot this motor is suppose to get. I took it out for a midnight cruise and things were fine as long as I was chugging at about 2,000 rpm. When I kicked it up to a nice cruising speed of 4,000 the temperature ran up from 140 to near 200 then I throttled back down and it took about 30 minutes or more for it to cool down below 160. This is a big heavy boat (24' cabin cruiser). I put a new long block in it last year with new impeller and thermostat and circulating water pump. It doesn't jump out of the water like a ski boat but will pull more like a freight train and sometimes will vibrate like one. I finially got the wiring straightened out so that it now has the original type of electric temp sending unit and gauge rather than the Sunco universal type temp gauge. With the old gauge it frequently showed 210 after running a while but never ran hotter and never "cooked". I did have a problem with a broken belt last summer right after puttin in the new block and ran hot one time. Now the oil pressure runs about 40 and at low rpm will look kinda scarey low. Cruising in at low idle in neutral I noticed oil pressure actually got up to 160. Thinking about pulling it out in the winter and replacing mains and rod bearings.... any thoughts on what may be causing it to heat up or is the 150-200 temp jump normal for a heavy boat?

 

[RandyJ]

Re: '78 bayliner monterey24' 350/260 runs hot

Bump...Hey you guys got any input on this?

 

[Scaaty]

Re: '78 bayliner monterey24' 350/260 runs hot

150-200 temp jump normal for a heavy boat?<br /><br />Not 200....my big 25/350 runs 140, with 40 pounds oil pressure

 

[Jilly - 5]

Re: '78 bayliner monterey24' 350/260 runs hot

Lots of questions first:<br /><br />1. Are you RW or FW cooled?<br />2. What block do you have (Ford, Chev, GM, etc)?<br />3. Is engine "nicely" at 4000 rpm or laboring?<br />4. Any trim tabs?<br /><br />Problem could be anywhere from a weak hose collapsing under pump suction at high rpm, to laboring with too much prop pitch, to sticking thermostat, to inoperative riser baffles, to non-linearity in your temp gauge, to .....etc etc etc. Are your manifolds too hot to hold your hand? Tell us more.

 

[RandyJ]

Re: '78 bayliner monterey24' 350/260 runs hot

Freshwater, Chevy 350 / mercruiser 260. Pretty much runs nicely at 4000 with light load(one to 3 adults)once on plane. Has hydraulic trim tabs that do not work very good so I keep them up. Manifolds are pretty much as hot as temp gauge indicates. At 140-150 I can put my hand on them. At 190 up they feel very hot under the soles of my tennis shoes. I have no reason to suspect cracked manifolds but haven't checked them either and don't know how without taking them off of engine or pulling spark plugs to check for water on them.

 

[RandyJ]

Re: '78 bayliner monterey24' 350/260 runs hot

Since the outdrive is from a 140 is there a possibility that the fw tube that passes thru the transom may be too small or maybe the hoses connected to it obstructed/pinched/kinked ?