HELP, engine running HOT! 2000 Moomba Mobius V

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!

Could be your circulating pump. Had mine go out in my boat at about 9 years.
This is the engine water pump driven by the belt, not the fresh water impeller.

Some times the impeller can break off and pieces will get lodged going into the transmission cooler, check it out, good luck!

The belt could be loose also. It tightens up by the alt.

If thats not it, Take the hose's off one at a time and blow through them. You might have a clog somewhere.

Change impeller and clean transmission heat exchanger.

make sure you don't have any air leaks from the thru hull to the water pump inlet, check the tightness of all hose clamps and the sea strainer bowl if you have one. A small air leak will cause the problems you are having. Make sure you don't have water coming out of your water pump, that it's sealed up properly after you put in the impeller.

Also make sure the o ring is properly seated in the raw water strainer.

maybe the thermostat!!

I second taking the hose off the transmission cooler. There is a screen that can get clogged up in there. This is quick and easy to check. Like everyone else said, start pulling lines off looking for some trash or a piece of an impeller.

Have you ran it since you changed the impeller. If not, then it may just be old and not moving as much water.

Thanks for the input guys, going to start in on it tonight, hopefully get it going by the weekend. Is there anyway to take a hose off of these and run a garden hose into it so I can run it without being on the water? THANKS!

(Message edited by schmidt18 on June 15, 2009)

yes, there's a very recent post about exactly that, with pics

Get a Fake-A-Lake or just make one out of a plunger from the hardware store.

By the way I would start with the raw water impeller (made of rubber and need to be changed every couple of seasons.) If that checks out to be ok then look at clogs in hoses as stated above. If that is good then pull the thermostat housing and replace the thermostat. P.S. if you don't know when the impeller was changed last just replace it when you have it apart. At that point you have done 98% of the work to change it and with the part being less than $35.00 cheap insurance and you don't have to worry about it for a couple years.

Fake-a-lake's blow. You'll have to crawl under the trailer to set it up. Then turn the water on. Then you'll be topside in the boat ready to start it & the thing will blow off the intake scooper & be blowing water everywhere but in the boat..... and you won't have any idea because it's under the boat & your topside.

For half the cost & way less hassle you can build yourself an adapter to plug your hose directly into the water intake.

Follow this thread

(Message edited by bill_airjunky on June 15, 2009)

Bill not sure why you have such a hatred for Fake-A-Lake's? Never had a problem with them in the 15+ years I have used them. Don't have to run a hose into my boat, don’t have to disconnect the supply hose to my v-drive and reinstall it and finally don't have to worry about water leaking inside boat. But to each his own if you like your way better than great. Just thought I would give him a fast easy way to run boat out of water. Not trying to get into a pissing match over the best way to hook you motor to a garden hose.

This isn't that cheap but is a nice system. I fyou wanted to get fancy you could even run a hose from it to a connection that goes through your transom.

http://bakesonline.com/detail.aspx?ID=821

Sorry Brandon. I used the fake-a-lake for over 10 yrs myself. And this spring I made the adapter listed in the other thread. I don't have any problem with water leaking anywhere inside the boat.

There have been quite a few guys on WW who had problems with their boats priming when using a fake-a-lake. Thats really what got me to build my own adapter.

I suppose the hatred comes from getting my 220 lb butt under the trailer every time I need to install or adjust the fake-a-lake. I just found it way easier for me to use a screwdriver & put a hose adapter in the boat where I can monitor how effective it is working..... rather than sliding under the trailer on my back & knocking my head on the trailer.

Sorry if it sounds like I'm attacking you. It wasn't meant to be a pissing match. Your right. Whatever method you like is what you should use. Just trying to give out an option that IMO works easier & more effective & costs less.

(Message edited by bill_airjunky on June 15, 2009)

No problem, guess I took it the wrong way no bad blood.

Alright guys, just got the transmission cooler off and flushed out. There was a few things in there, some weeds and a small stick. Not too much though, how much would it take to plug it up enough to heat up?

I did go ahead and build a plunger for right now, I'll end up building the other one too and decide which is best.

THANKS!

Quick Update: As I mentioned above I did get a little debris out of the transmission cooler, I don't think it would be enough to restrict the water flow to the point of it getting hot, but I'm not real sure.

I have taken all the intake lines off of the boat and everything is clear, no blockages. I started it up and ran it for about 15 - 20 minutes and the temperature gauge never went above 150ish. However, I'm not sure how long it would take to warm up, I would have left it on longer but my oil pressure gauge was bouncing around 60 - 80 then started to bounce enough to spike and finally staying above 80, which is the highest the gauge goes. I shut it down after about 3-5 seconds of it resting above 80. What would cause this? I'm wondering if I didn't have the plunger seated well enough or if that would matter? Could I have bumped something in the process of pulling hoses that would cause this?

Now it seems I have two problems and still need help with both, do I just go try a lake test and see how it performs or am I missing something? Looking forward to hearing some suggestions. THANKS!

OK, wiggled some wires around down near the transmission cooler and the gauge un-pegged. Must have a bare wire down there, not a huge deal. Just shook it somemore and now the gauge is stuck at 0. Any idea where the switch/sensor that controls this gauge is located at?

Now just need to know how long it should take for the engine to heat up above 160 at idle. I can not throw the engine in gear without actually being in the water correct? The shaft has to be fully submerged so the seal gets wet I am assuming?

Just ran the boat at idle for 1 hour, engine cover shut, no wind & about 95 degrees air temperature. Took about 15 minutes to climb to 160 but never passed 180. I assume this would mean that it is working correctly? I never throttled the engine above idle. Please let me know your thoughts, would like to get it on the water tomorrow night.

By the way, I really appreciate all of your guys' help on this, it's saving me a ton I'm sure. THANKS!

Really need to throttle it up to be sure it won't overheat, best to put in the water and run wide open for about 5-10 minutes to be sure. But since it d overheated that much before pay very close attention to the engine and your gauges while running, could have possibly caused some damage to the internals.

you should be able to run the boat at 3000rpm or so for about 30 seconds but you need to be careful you don't starve the motor for cooling water. Listen very carefully to the exhaust note. If it starts to get louder you are starving the motor from water, bring it back down to idle or shut it off.

You should always listen very carefully to the exhaust note anyway whenever you are trying to diagnose a cooling issue. Louder exhaust than normal is often the first clue of lack of cooling water supply, steam from the exhaust is often the second clue. These two indicators can tell you as much or more than the gauge in the dash.

STILL NEED HELP!!!

Well guys, just got back from the lake, 20 minute run and it was up to 200-220 again. I really need to figure this thing out. Why does it heat up when I have the boat in gear? It sat for an hour out of gear at idle last night and never climbed above 180. Someone please shine some light on this for me PLEASE! THANKS>

(Message edited by Schmidt18 on June 17, 2009)

Three things:

1. Your garden hose is forcing water through the motor so essentially your impeller could have shredded all of its veins and the motor would still get water because your garden hose is forcing the water through at 50-60 psi.

2. The motor makes way more heat when under load than it does just idling.

3. Finally when on a garden hose you have a constant stream of 55 degree water coming into the engine from you water. Based on your geothermal temp in KS. Your lake water has a surface temp of mid to high 60's. Your cooling water is 10 - 15 degrees warmer before it ever absorbs any heat from the motor. So the same amount of lake water can absorb less BTU's than tap water.

I still put my money on what I stated earlier.

"By the way I would start with the raw water impeller (made of rubber and need to be changed every couple of seasons.) If that checks out to be ok then look at clogs in hoses as stated above. If that is good then pull the thermostat housing and replace the thermostat. P.S. if you don't know when the impeller was changed last just replace it when you have it apart. At that point you have done 98% of the work to change it and with the part being less than $35.00 cheap insurance and you don't have to worry about it for a couple years."

I did replace the impeller before this all started hapening. I'm pretty sure there is only one way the to install the impeller, however, I did forget to replace the seal, how much would this matter?

Also, how does the thermostat work on this engine, I read somewhere that stated it opened at 160 degrees, if this is the case then I would believe that the thermostat could be the problem.

Is there a way to tell if the thermostat is bad once you pull it out? THANKS

(Message edited by schmidt18 on June 18, 2009)

The seal is very important. If any air gets into the system it will not get the suction to get the water flowing.

To check the thermostat put some water in a pot throw the thermostat in then boil it and when it opens you check the water temp with a thermometer. This is the way Ive checked automotive thermostats before. A mechanic buddy of mine checks new ones before install as well. I guess 1 out of 15 or so dont actually work right.

When I pulled the thermostat out, it looked old and kind of rusty so I rinsed it and put it back in, there could be a good chance that it is bad. Going to replace it, just hope I can get one near by, they are cheap but overnight shipping is not.

I didn't see or feel any leaks around the impeller when the engine was on, I may pull the cover back off and replace the seal just in case, that's easy enough to do.

Thanks again for all your help!

Well, got mine on the water today with the new thermostat and I am back in business, engine cooling is back to normal.

Now, I just need to find the loose connection going to the Oil Pressure Switch/Sensor, can someone tell me which side of the engine this is located?

Thanks for all your help guys!