Water pressure questions 140hp 2.0L looper

[Magnum1500]

I have just installed a pressure gauge on the cooling system of my 140 HP looper. I get a reading of around 5 psig when engine is running on muffs from garden hose at a fast ilde 1000 rpm.<br /><br />I plan to raise motor on jacking plate to increase boat speed.<br /><br />1) what pressure should I expect at around 50-60 mph and 6000 rpm?<br /><br />2) what is the minimum safe pressure that you would want to see at WOT 6000 rpm and 60 mph to prevent engine damage?

 

[Dhadley]

Re: Water pressure questions 140hp 2.0L looper

Water pressure depends on which pump, what gauge and which flow system youre using. <br /><br />A general rule of thumb -- 18 lbs is the minimum "safe" pressure at or near wot. At 15 the motor won't like it but will live -- probably -- if everything else is correct. Less than 15 it wont live long at wot.<br /><br />And this is assuming we're talking about solid water flow, not aeriated water.

 

[Magnum1500]

Re: Water pressure questions 140hp 2.0L looper

Thanks Dhadley. <br /><br />One more question.<br /><br />When I fired up the motor at home with the muffs and garden hose, water started to only dribble from the tell tale for maybe 10-15 seconds and there was a zero pressure reading on the water pressure gauge. Then after the 10-15 seconds the neddle shot up to 5 psig.<br /><br />Is this normal? for the system to prime it self, or should I take a closer look at the pump.

 

[Dhadley]

Re: Water pressure questions 140hp 2.0L looper

Sounds about right. The water cavity in a looper is pretty big. However, if you havent changed the pump in a couple of years, it might be an opportune time.

 

[Magnum1500]

Re: Water pressure questions 140hp 2.0L looper

Hi Dale,<br /><br />Went skiing on the weekend.<br /><br />Have not jacked engine yet.<br /><br />Got 5 psig at idle in neutral<br /><br />Got 7 psig at idle in gear (fwd)<br /><br />got 10-12 psig at 3500 rpm and at 25-30 mph skiing speeds<br /><br />At WOT (6000 rpm and around 55 mph) with 13.25" x 19" OMC factory prop the needle on the gauge was dancing all over the place between 12 - 16 psig. Real unstable reading all right.<br /><br />I did not have a liquid filled gauge, perhaps it would have been more stable if I had one?<br /><br />Is it likely that aerated water is geeting into the pick-ups and causing the fluctuating pressure?<br /><br />I only ran the motor for 20-30 secs at WOT and backed out of it. Temp gauge did not move up from the normal operating posn.

 

[Dhadley]

Re: Water pressure questions 140hp 2.0L looper

The reading should be steady. And it should be more than that at wot. Are you sure it's reading pressure from the adaptor plate? It's not T'd into the overboard line, right?

 

[jy118lfd]

Re: Water pressure questions 140hp 2.0L looper

Sounds like you tee'd into the overboard indicator

 

[Magnum1500]

Re: Water pressure questions 140hp 2.0L looper

I tee'd into the flexible line on the RHS of the power head that originates from a 1/8" NPT tapping at the bottom rear of the powerhead very close to the fibreglass lower cowl.<br /><br />My description might be a bit vague, I will detail it more if you want, but I will need to wait to i get home and have another look.<br /><br />Where is the proper place to take the reading from?

 

[jy118lfd]

Re: Water pressure questions 140hp 2.0L looper

Sounds right. try lowering the motor a bit and see if it helps. <br />If you haven't changed the pump recently you shoud consider it

 

[Dhadley]

Re: Water pressure questions 140hp 2.0L looper

Thats the right place. The idle pressure indicates its in the right place but the wot shouldnt jump around like that. When it did that you were holding a steady throttle, right?

 

[Magnum1500]

Re: Water pressure questions 140hp 2.0L looper

Yes, I got a foot throttle and it was pushed hard down. My mechanic assures me that the pump casing although not new are in excellent condition, but I have not seen this myself to verify. I will drop the leg and have a look.<br /><br />Do you think that the water pickups a catching aerated water at full throttle? The gauge is only flickering between the 12 and 16 psig marks.<br /><br />Is it the motor likely to develop hot spots in the water jacket if I continue to run it in this condition?<br /><br />My Mechanic runs a 2006 225 V6 High Output (He reakons it is 267 Hp at the prop) on a real light weight 18ft kevlar V-bottom. He says not to panick as he only get 7 psig at WOT on his boat. Even though he has good basic mecahnical skills working on outboards, he has limited performance and racing experience, since he has only just set his own boat up over XMAS.

 

[Dhadley]

Re: Water pressure questions 140hp 2.0L looper

Ah, the pump housing "looked" OK so it wasn't replaced. Lets go ahead and complete the job with a new liner and plate. You might look into it and find out the parts we need now are more money than a kit. Dont know for sure. <br /><br />What kind of boat are you running?<br /><br />BTW -- you "mechanic" is running more than 7 lbs at wot. If that was true he'd be changing pistons by now. I'd be real curious about his "rekon meter" too.