raw water pump v. engine water pump v thermostat v ???

[ers906]

How can you tell the difference between a problem with the raw water pump and the engine cooling pump, the thermostat freezing or something different?

Today was out on the water and the boat ran fine for about ten minutes, when we stopped and waited for the ballast to fill. When started to ride, the temp spiked at around 190. Shut it down and it immediately went down. Initially at idle the temp stayed at 160, but when increased to 20-25 mph the temp spiked again and the engine went into limp mode. I was able to motor at 5 mph and the remained normal. Took apart the raw water intake, ensured all the hose clamps are tight, and checked the impeller. The gasket on the stainer was intact. But there does not seem to be any water flow through the strainer. I took off the hose between the intake and the raw water pump and placed it in a bucket of water (all done while on the lake) and it did not seem to be sucking any water through the engine.

Any ideas what can be the problem? Would a stuck thermostat not allow water to be sucked through the engine? POssible bad raw water pump? Now that I have the boat on the trailer at my house, where would the logical first step being to figure out the problem? Any help would be appreciated. (sorry for the ramble, it has been a long day, first day out with the girlfriends kids and the boat doesnt work, FML)

[Mamigacz]

I don't think your thermostat is bad.

If its holding temperature at idle, the thermostat is doing its job. Something is restricting flow.

If the raw water pump is bad, You should be able to feel the exhaust riser for excessive heat. If you can't touch them, or if burnt rubber smells are noticed, there is most likely restricted flow in the raw water pump circuit. The raw water pump's two jobs are to bring cool lake water to the engine and the exhause risers. When the thermostat is shut cool lake water is still flowing through the exhaust risers. When the thermostat opens, cool water goes into the engine, while hot water flows into the exhaust riser. This cycle of open and closing will keep the temperature down on the risers.

If the circulation pump is bad, it would be weeping water (A sign of seal failure) bfrom the bottom of it. My thoughts are:

Bad raw pump impeller
blockage between the raw water pump and inlet
blockage in the water jackets of the engine.

If you want I can give you proceedure on testing the raw water pump?

[vision]

Mamigacz analysis is correct.

But, considering the raw water intake through pump appears normal and there was no gross evidence of a raw water intake blockage or vacuum leak on your inspection, and no obvious damage to raw water pump/impeller, I would actually still replace the thermostat if this is your 2002 Super Air.

The symptoms are not characteristic of a bad thermostat, but I have learned the hard way that a bad thermostat does not allows result in the expected type of over heating.

[Quinner]

Excalibur, GT-40 or other? When you ran off the bucket was there any bubbles which could indicate pump installed backwards? Was the valve for water intake in open position??

I would be leaning towards impeller issue or air coming in somewhere before the pump, start by checking there.

Bummer your day got screwed up, hopefully an easy fix for ya.

[Mamigacz]

Just curious. Your doing this all in the water, right? when you disconnected the intake hose didn't a flood of water come through from the lake, after you dissconnected it?

I addition to Quinners suggestion:

I would try hooking the garden hose up the oulet of the raw water pump (bypass the raw water pump). If the flow of water from the garden hose travels to the risers (and out the exhaust) and the engine holds temperature, the odds of having a defenctive impeller will be alot greater. I would guess, you would have to hold the engine RPM on the trailer at 3000 to see if the engine gets hot.

[ers906]

I turned off the main intake while disconnecting the hoses, checking the raw water pump etc. I am going to take apart the entire system tomorrow on my day off after I initially bypass the raw water pump. If that is normal, then i will do the same on the other side of the raw water pump. I figure that will allow me isolate the water pump/impeller as a source of the problems. I will likely replace the thermostat since I am selling the boat and figure since I will be working on the engine, it will be one less part for the new owner to worry about. Same with the impeller. If the problem isnt obvious, I will just keep moving down the line to look for where there is a water flow obstruction. This sound like a solid plan?

[Mamigacz]

Sure does. I'm curious what the outcome is.

[JayG80]

I have heard that the impeller can appear fine but the rubber fins can spin around the hub

[Quinner]

I have heard that the impeller can appear fine but the rubber fins can spin around the hub

Great point, Just happened on my buddies boat when we put it in this year, the brass hub broke so was not turning the vanes. Had to really look at it to see it was broken.

[azeus17]

If you took off the suction side of the RWP and put in a bucket and did not notice any water being sucked out, I would be willing to bet it is your impeller. It should suck that bucket dry in seconds. I assume it was all working when you put her to bed last fall. Did you take anything apart to winterize that could have been put on backwards?

[DanielC]

This is a thread on a flushing adapter I made.
http://www.planetnautique.com/vb3/sh...ushing+adapter

The thread describes how I use it to check for leaks before the raw water pump, by pressurizing that side of the cooling system. Remember, a small water leak is a big air leak. Also remember, with V-drive boats, there is a lot of hose, connections, V-drive coolers, Transmission coolers and other stuff between the water intake on the hull, and the raw water pump on the engine.

With my adapter, a GM 5.7 engine could suck more water than my garden hose would put out, AT IDLE RPM. A GT-40 engine started using more water than the hose around 900 to 1,100 RPM.

[High altitude]

I would guess, you would have to hold the engine RPM on the trailer at 3000 to see if the engine gets hot.

That would be a mistake to run it at those RPMs off a hose. You will solve this problem..but it takes some patience. Don't compound the problem with an even bigger one. JMHO.-Marc

[Rick]

Don't discount an air leak in the strainer bowl. If air leaks in through the O-ring things might look normal but your sucking air past the strainer.

[Mamigacz]

The rubber coming loose from the hub, is a very good point. Before trying anything, that impeller should be taken out of the housing to check for damage.

I have ran an engine (351W) off the garden hose while breaking in my cam. The engine RPM's were varied between 1500 and 3000 for a period of 20 minutes. The engine temperature stayed rock steady at 140 and I could touch the exhaust risers whole time. If there is something else that would damage the engine, I would be curious what it is?

[Quinner]

As Daniel pointed out, if you are directly connected to the hose at higher RPM's it will draw faster then the typical hose flow, if using a bucket method it's not a problem if you start with a full bucket, water level will be visible making it clear if you are running low on water and need to reduce RPM. As long as you are getting adequate water, High RPM's are not a problem on the trailer.