2001 135 Optimax overheating at idle

[180combo]

My temp gauge climbs steady up to the point the alarm goes off and reduces power on the engine. I have good flow from the tale tell. There is a magical RPM where the temp will imediately fall. When in the overtemp alarm, in neutral rev the engine and about 1800 RPM's or so the temp plunges back to normal. This is annoying. Makes it almost impossible to pull skiers because while idling waiting for the skier, as soon as they are ready to go when you hit it the engine goes into alarm and shuts power down. Any ideas? The impeller has been replaced and seems to make it better for a short time.

 

[ronnieboy]

Re: 2001 135 Optimax overheating at idle

bet its the thermostats. increasing rpm and pressure makes a sticky thermo unstick and operate like it should, worth a try, they are cheap( compared to other parts! ) good luck ron

 

[WillyBWright]

Re: 2001 135 Optimax overheating at idle

One or both thermostats are sticking. There's a bypass valve that opens at higher RPMs and cools the motor regardless of what the thermostats are doing.

 

[180combo]

Re: 2001 135 Optimax overheating at idle

Thanks guys! I will have a look see at these thermostats. Are 2001 manuals available for this motor?

 

[down_time_1]

Re: 2001 135 Optimax overheating at idle

180combo,<br /> I had a 2000 115 opti (only made 18 mo.)it,sence been replaced with a 2004 150efi, but still have the merc manuel and the 4 guage light worning system . If your interested in them i'll let them go cheep as i have no use of them now.<br /> DT1

 

[Texasmark]

Re: 2001 135 Optimax overheating at idle

Had a stuck therm in a different Merc. Telltale just says that water is "available" for use in the engine. If it were were generated by block water, there would be no tell tale until the thermo opened. I was falsely reassured as my telltale was excellent.<br /><br />The bypass is a pressure bypass that allows direct cooling water (in a much larger volume) to circulate through the engine when you get ram water into the water inlets on front of the skeg....like when you are on plane and faster.<br /><br />I don't know if the water pump can develop enough pressure to open it at high rpm's idling. I doubt it as the impeller blades fold back at high pressures, but that might be high pressures caused by ram water input, not impeller revolving speed.<br /><br />So with my problem at slow speed or idle, the horn was on. I had just bought the rig and this was a surprise to me. To get back home I put her on plane (20-25 mph) and after about a minute the horn turned off. Apparently had enough pressure to open the bypass valve.<br /><br />Upon arriving in the no wake zone near the launch, I had to slow down to a crawl and it sounded again. Shut her down and used the trolling motor to get to the launch.<br /><br />Later at home I verified my stuck therm in a pot of water. Took it out (of the engine) and no more alarm.....but I just bought a new one and installed it to help warm the engine when boating in cold weather. Seems these newer EPA compliant 2 strokes are fuel strangled to the point where they don't want to keep running when you first start them up. I'm thinking the stat will help.....once I get it started.<br /><br />HTH<br /><br />Mark

 

[180combo]

Re: 2001 135 Optimax overheating at idle

Mark, <br />I can get the engine to cool down in neutral by getting the revs above about 1800 rpm's. And the cooling is very rapid at the magic rpm. Has nothing to do with planning speeds at all. Does this change your trouble shooting thoughts?<br /><br />DT1, I am interested for sure in the manual but what is a 4 guage light warning system?<br /><br /><br />Greg

 

[180combo]

Re: 2001 135 Optimax overheating at idle

Can anyone give a clue as to where on the engine I should be looking for these t-stats? At the top of the cylinder heads right?

 

[180combo]

Re: 2001 135 Optimax overheating at idle

Ok, got the old t-stats out and compared them to new ones in hot water... both old and new opened at the same time. the new ones look like they may be openng very slightly more than the old ones. I doubt this very slight difference could actually cause overheating at idle. <br />New stats are installed but I have not put the boat back in the water yet. I am really not very optimistic about my optimax running cool at idle now.

 

[andy6374]

Re: 2001 135 Optimax overheating at idle

Don't know until you try.<br /><br />When's the last time the waterpump was rebuilt or the relief valve assembly replaced?

 

[180combo]

Re: 2001 135 Optimax overheating at idle

the impeller was replaced a couple seasons ago and made no real difference to the temps at idle. The motor does not get a whole lot of use so other than being a couple years old the impeller has low hours on it. <br />The relief valves have not been touched. <br />What do the relief valves have to do with idle temps? I thought those were designed to open as RPM's increased. I only have temps rising while at idle speeds.

 

[andy6374]

Re: 2001 135 Optimax overheating at idle

The poppet valve (part of the pressure relief assembly) is designed to open at higher RPMs (2500-3000) to dump excess water from the block and promote better flow (as you mentioned). However, if the poppet is stuck open at idle speeds it is dumping water from the block at idle speeds and thus your block will never fill with water and will overheat. This is a frequent cause for overheating at idle, do a search on it.<br /><br />Just because the impeller has low hours on doesn't mean a thing. The rubber can get dry rot amongst other things. It should really be replaced every 2 seasons, along with the tstats and poppet assembly.

 

[andy6374]

Re: 2001 135 Optimax overheating at idle

The poppet valve (part of the pressure relief assembly) is designed to open at higher RPMs (2500-3000) to dump excess water from the block and promote better flow (as you mentioned). However, if the poppet is stuck open at idle speeds it is dumping water from the block at idle speeds and thus your block will never fill with water and will overheat. This is a frequent cause for overheating at idle, do a search on it.<br /><br />Just because the impeller has low hours on doesn't mean a thing. The rubber can get dry rot amongst other things. It should really be replaced every 2 seasons, along with the tstats and poppet assembly.

 

[180combo]

Re: 2001 135 Optimax overheating at idle

ok, more info. Took the boat out after the t-stats were replaced. No change. still getting hot at idle. took note of water pressure. at idle there is only about .5 psi read by the system. at 3500 rpm and at 30 MPH there is about 6 psi. this does not really sound like enough to me. brought the boat home and put it on the water hose. engine would not overheat on the garden hose but still noted only .5 psi or less at idle. I would assume because there is pressure applied to the impeller from the hose that it would possibly function better. So the lower unit is coming off and a new impeller will be installed.

 

[gss036]

Re: 2001 135 Optimax overheating at idle

I would suggest that you follow the above given suggestion and change the poppit valve as that is probably where the real problem lies. Your water pressure should be around 2 psi at idle and 12 psi at 4500+. So both would be good move.

 

[Texasmark]

Re: 2001 135 Optimax overheating at idle

Back to my problem. I had just bought my engine and had not joined this forum. So I guess I was lucky that my particular problem was indeed the therm. <br /><br />Now that I am more versed, I agree that the poppet could be the problem. I ran my boat up on plane as I didn't know I had a poppet and if I had a water pump delivery problem, the forward speed pressure from water forced into the lower unit should have solved my problem at speed. It was solved, so I guess the poppet opened now that I know I have one. I did not know to run the engine over 2000 rpm's in N to get the poppet to open so I don't know if it would have cooled at fast idle or not.<br /><br /><br />Also, on impellers, if the engine sits without being turned over periodically, your impeller can take a "set". The water pump is deliberately eccentric. So part of the impeller has the blaces forced back and the other part has them almost completely relaxed. If it takes a set, when it's time for it to pick up water (relaxed position) it doesn't contact the wall of the pump (due to the set from the compression side) and it can't move adequate water.<br /><br />The water hose proved that for you. <br /><br /><br />On pressures, I can't help, but .5psig is really tiny. I'll go with the impeller and due to the pressure and what gss said that it shuld be, redo the poppet and spring that holds it shut.<br /><br />My 2c,<br /><br />Mark

 

[180combo]

Re: 2001 135 Optimax overheating at idle

so looking at the impeller, the correct shape is the blades are bending towards the direction of turn?

 

[KCLOST]

Re: 2001 135 Optimax overheating at idle

No,<br /><br />The blades should bend in the opposite direction of turn.. The blades will bend in a counterclockwise direction! But the impeller turns in a clockwise direction. (when you look at it from above) And don't forget the impeller key!

 

[180combo]

Re: 2001 135 Optimax overheating at idle

I have replaced the t'stats, water pump(everything except the bottom section), and poppet valve and spring. Everything that has been suggested so far. While the poppet assy was removed I verified I had water coming from the top of the block that dumps into the poppet assy so it appears the motor is filling with water. I am only able to develope about 1 PSI of water pressure at idle until the t-stats open and then only about .5 PSI. This engine will not overheat while running on a garden hose- possibly due to the lack of any engine exhaust back pressure out of the water. In another thread related to this same engine it was mentioned that Mercury had increased the size of the water tube from the water pump by about 50% with out changing the pump to increase volume. Are there any ideas related to this possibilty? Please, I am just about out of ideas.<br /><br />Greg

 

[180combo]

Re: 2001 135 Optimax overheating at idle

Anyone have a plumbing diagram for this engine? I would like to see if I can pin down some sort of blockage somewhere.