HELP, engine running HOT!

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!

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.

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.

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.

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.

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!

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

It's right here under DIY fake a lake:

https://forum.moomba.com/showthread....hlight=plunger

Awesome, thanks guys. I also read that I can just make an adapter to tie into the intake side at the tranny cooler. Are both options just personal preference or would it matter too much one way or the other? THANKS

Preference. The fake a lake thing is just real easy.

Preference...hose to the inlet of VDrive.. I added a water hose shutoff at the adapter......no driveway mess while not running.

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!

How fast were you running the engine?

Engine was at idle, I never sped it up at all. Went back about 30 minutes later and turned the key on and the gauge was still pegged? Any chance a knocked a wire off of the switch? Let me know. THANKS.

Tap on those gauges if they are reading odd first. Hate to say it, but sometimes they settle back in with a knuckle bump.

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!

How long after it warmed to 160 did it run?

It ran for about 40 - 45 minutes after it got to 160.

that was ample time to overheat, and if it would heat up to too hot in that time frame before you inspected and cleaned out the system, and you have now ran it and it didnt heat up like before, I would say you are good to go.

Yeah, that's kind of what I am thinking, only part I couldn't really test is actually putting it in gear to see if that had anything to do with it. Going to try and do a lake test tonight so we'll see how it goes. I'll let everyone know. THANKS!

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>

I would sure change out the thermostat and make sure that it is not clogged.

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

You dont have any leaks around the impeller right?

Was the old impeller in good shape or was it wore completely down?

It sounds like the previous owner had the same problem, and maybe was guessing at the impeller.

The thermostat sits in its housing at the top of the engine and is spring loaded with a copper element. As the engine heats up, the copper heats and the spring loses tension at the designed temperature, in our case 160F.

One way to test it is to remove it and place it in a pot of water on the stove, and using a thermometer raise the temperature to 160 and gradually raise from there, and ensure that it is opening.

If it looks corroded, chances are it was sticking or not fully opening. Thermostats are inexpensive to replace, and as well there are chances that the thermostat or housing has debris in it.

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!

Quote:

---

Originally Posted by dereklschmidt

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!

---

As long as you know the temp for the thermostat (or part #) you can get tehm at any autoparts store. Nothing special about them.

I'm having the exact same problem. I changed the impeller looked at the lines, etc. I have taken my thermostat off and tested it in hot water and it is opening but I'm not sure if it is all the way. Since I already have it all apart I'm going to go ahead and put a new one in there. I'll let you know what I find out.

BTW, I do have a clear strainer and it is pumping water but I'm not sure of how much the flow should be. Someone told me that I should be able to put my hand on the exhaust for a couple of seconds before taking it off.

Yeah, please let me know what you find out, I'm going to replace my thermostat but the weather doesn't sound like it's going to allow me to get the boat on the water anywhere in the next few days. Thanks.

Ok, I got the boat on the water with the new impeller and thermostat and had the same problem. I checked everything and the only thing I can come up with is the water pump/circulating pump. I took off the big hose that goes from the pump to the thermostat housing and had my wife start the engine. No water at all came out of the hose even thought there was still water in it. I assume that that has to be the problem. So I will tackle that next. I'll let you know what I find.

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!

Glad to hear you're up and running again.

Quote:

---

Originally Posted by 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.

---

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

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.