Comp test does water need to be flowing?

[10 FOOT INVADER]

Going to run a comp test on engine. Do I need to have muffs on and water circulating? The engine will be turning over so I think water should be flowing.

 

[Don S]

Re: Comp test does water need to be flowing?

No,
You won't be spinning the engine long or fast enough to cause a problem

 

[thrasher]

Re: Comp test does water need to be flowing?

As Don saya, NO. You must disconnect all the spark plug leads and remove all the spark plugs. This prevents the engine from starting (so no need for cooling water to be flowing) make sure the throttle is fully open, then screw the compression tester into the required cylinder and turn the engine over with the electric starter. let it turn for 3 to 5 seconds to get a stable reading. write down the reading and the cylinder number then test the next cylinder. You want there to be less than 10% difference across all the readings if your engine is in good condition and yoou want to see something around the 150 or higher PSI range. If you get more than 10% variation you might correct it by putting the plugs back in and starting the engine and running a top end motor cleaner through the carb inlet, will smoke a lot. Then retest.. If the readings are below 150PSI then you have a tired engine and will want to plan on a fresh-up of the engine in the not to distant future!!

 

[Maclin]

Re: Comp test does water need to be flowing?

Not sure what drive 10 Foot Invader has so this may not be relevant, but on a system with the raw water pump up front on the engine is it a concern that the impeller could eventually get dry even if the engine is only turning on starter motor power??

 

[bruceb58]

Re: Comp test does water need to be flowing?

I know it is only going to turn a few revolutions every time you test one cylinder but, if you have water available, why not just hook it up just to be safe? Just turn it on very slow...that way you will have water at the pump.

 

[Don S]

Re: Comp test does water need to be flowing?

Heat is what causes the impellers to go bad when there is no water. And during a compression test, there isn't a chance to build up any heat.
Stop being so parinoid.
On a compression test, the max number of revolutions for each cylinder is 5 or 6. Now consider the pump is either driven by the drive or by a belt, and they are not 1 to 1 so you would have even less and slower revolutions of the pump.
No, you don't need water running. That stuff is expensive to run for no reason.

 

[10 FOOT INVADER]

Re: Comp test does water need to be flowing?

Thanks for the info. I will wait on the comp test. Taking it out to the lake in the morning. Have used it 3 times but never towed or backed it down a ramp. My mini van pulled my little invader just fine. My lincoln town car gets the duty for this boat. 20 foot monterey with a 305 merc boat weight near 2800lbs. With trailor and gear has to be atleast 3500lbs. My t car states with a towing package can handle 5000lbs. I installed a tranny cooler power steering cooler and a 4 core radiator. New brake pads and shoes. I will be testing the brakes while towing around a mall parking lot to get a feel for it. 20 foot boat on the water sure got a whole lot larger out of the water. Thanks again.

 

[Haut Medoc]

Re: Comp test does water need to be flowing?

Good luck, btw anything below 150 psi is not tired.....
Anything below 120 is getting tired, with 100 psi being the bottom line....

 

[Robj]

Re: Comp test does water need to be flowing?

Good luck, btw anything below 150 psi is not tired.....
Anything below 120 is getting tired, with 100 psi being the bottom line....

I agree, there are engines below 150 that are not tired.

Have a great day,

Rob.

 

[bruceb58]

Re: Comp test does water need to be flowing?

No, you don't need water running. That stuff is expensive to run for no reason.

Hey Don...I respect your opinion and you may be 100% correct but we aren't using bottled water here. Turning it on with just a trickle would suffice for a test like this as long as the water makes its way to the pump.

I have a spare pump for my LK series Volvo that is driven off a belt. It is extremely hard to turn when it is dry so there is a large amount of friction. I believe that is why they supply the jelly when you install a new impeller. Since the pulley on this pump is smaller than the crankshaft pulley that drives it, it actually turns considerably more revolutions than the motor turns.