HELP, engine running HOT!

[dereklschmidt]

Hey guys, I'm new to the boards and just picked up my Moomba back in April. It's a 2000 Mobius V with the 5.7L V8 Indmar in it. It's sitting at about 840 hours right now. It's been pretty well taken care of and ran into my first issue.

Last weekend, on the last run of the day, we noticed that the temp gauge got up above 180 for the first time. When we throttled up the temperature went back down to normal, but when we were idling around it would slowly climb back up. When I bought the boat, the previous owner gave me a new impeller and said that it would need replaced in the next 10 or so hours. I assumed this was the problem and replaced it this morning.

We got it out on the water today and the temperature just kept rising, didn't matter if we were idling, cruising, or at a dead stop, it kept rising. I shut her down when it got close to the 240 mark and let it cool off. When I started it back up it slowly started to rise again. If I stayed out of gear and just reved the engine above 2500 RPM or so, the temperature gauge slowly dropped back down to the normal 160 range.

This is where I am lost and need your help, I checked the metal strainer on the bottom of the boat and it was clear, is there another filter or strainer of some sort that could be plugged and not be getting enough water when we are moving?

I am trying to avoid taking it in to a dealership as things are pretty tight right now. This is my first true inboard I have owned and I'm not too bad at working on things so I would like to figure this out with your help. Please let me know if you guys have any suggestions or where to start. THANKS!

[Razzman]

How was the old impeller? Was it missing any part of it? Did you check the thru-hull strainer intake for blockage? Sounds to me like you have a block somewhere in the cooling system. If pieces are missing they can get trapped in the system and you have to dig them out.

[gcnettl]

Ok, so you changed the impeller, to no avail.

Your thermostat could be not opening, or not operating properly.

If you take the outlet hose off of the impeller housing, while your boat is in the water, and then crank up, it should throw some water out of that outlet.

While running, do you notice any play in your water pump? That is a good bit of hours on one water pump. It could be not pumping well after this time.

It really sounds like the thermostat or the water pump.

[maxpower220]

What was the condition of the old impeller that you took out. If it was in pieces, it is possible that some of that is clogging you engine block.
It is also possible to have sediment from your lake making some type of a block, you should know if that is possible based on the lake that you operate in.

[Razzman]

I'll gaurantee it's not the thermostat as this condition only applies when at idle. A thermo either opens or it doesn't. As he can get down to 160 with rpm's then that eliminates that one.

It's also not the circulating water pump, they either work or don't. If they don't then they blow the relief valve and water spews everwhere. They have brass internals so they don't corrode and deteriate.

As i said above I'll bet it's either a blockage due to a large impeller vane that broke off and lodged in the system.

I can't say if a 2000 has a water strainer but if it does it could be blocked or full of debris as well. It would be after the thru-hull but before the raw water pump.

Another possibility if i remember correctly, the transmission cooler. If that's clogged i think it can cause that problem as well. It's a long cylindrical thingy with hoses attached that usually sits down low along side the engine.

[dereklschmidt]

Thanks guys, I am going to start in on it tonight and hopefully get it going by the weekend. Is there anyway to hook a garden hose up to these engines so I can run it without being on the water? Also, the Impeller was ripped and tore a bit, but no missing rubber from what I can tell. I'll let you know what I find out tonight. THANKS!

[kaneboats]

YOu can make your own "fake a lake". Do a search on "plunger" and you'll find it.

[LSV_Flying]

Ok, so you changed the impeller, to no avail.

Your thermostat could be not opening, or not operating properly.

If you take the outlet hose off of the impeller housing, while your boat is in the water, and then crank up, it should throw some water out of that outlet.

While running, do you notice any play in your water pump? That is a good bit of hours on one water pump. It could be not pumping well after this time.

It really sounds like the thermostat or the water pump.

I've had a lot of trouble with my thermostat on the same engine (replaced it 3 times) but, when it goes it opens up meaning you cannot get the engine to heat up b/c cold water keeps rushing through the water jackets.

check with the folks at Discount Inboard marine, LLC (http://www.skidim.com/) -- they are awesome.

Good luck

[buzcoats]

I took the water pump off and it looked good. The thing is pretty simple, it's like an impeller but has a metal cage on it. It appeared to be fine. Not sure where to go from here. Maybe I'll just make sure all the lines are clear. Hopefully I can figure this out before the season is over.