2003 mercury 150 saltwater carb motor running hot at full speed...HELP

[merc150]

Hey guys I have a 2003 mercury 150 saltwater CARB motor with maybe 350-400 hours on it. I have been having problems for the past month with it running at about 180-185 at 4000 rpms. It will run at 140 to 160 or so from idle to mid rpm range then it gets up to 180-185 at 4000 to 5000 rpms. I have changed the water pump about 5 months ago (mercury pump kit), I recently gutted the thermostats and changed the poppet valve and its still doing it. The water flow though the telltale is very strong. (before I changed the poppet valve I had the opposite problem it would run hot when going slow through a no wake and at mid throttle then cool down to 160 at full throttle). The guage (Teleflex sahara) and temp sending unit are new. I do not get a overheat alarm (yes it has been checked and is working). Before this past month the motor has always ran at 160 degrees no matter what. I fish a lot of redfish tournaments so im trying to get this figured out as soon as possible. One other thing both of my mercury dealers are telling me 180 is way to hot and that the warning alarm should come on at about 190 degress BUT my seloc mercury manual says that the warning alarm should turn on at 232-248 degrees I don't know which one to believe. I also removed the oil pump about a year ago and I have been mixing the oil 50:1. Other than that the motor is very strong and runs great. ANY help will be greatly appreciated!!!! THANKS

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

bump.

 

[1nebel0]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

Well the poppet valve would have been suspect for me but you changed it...what do you mean you gutted the therms? If you took them out you are asking for problems as only the Bridgeports run washers and no therms due to wanting to dump the water ASAP given the heat and rpm's these motors spin...My friend cold siezed his 200 by not running therms...very simply stated the pistons are expanding and the cylinders are cold due to the water running out of the motor and over cooling it. Next thing that happens is the pistons scuff the cylinder walls that didn't expand with the piston getting warm and the cylinder running too cold...You idle temps don't indicate that..You got a wierd one on your hands for sure...blockage somewhere...Every melt an impeller?

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

Thanks for the reply!! I removed the spring on each thermostat and just stuck the t stat housing and seal back in so its like the thermostats are open all all the time and still has the housing to slow the water down. (my merc mechanics recommended it) I live in florida and the water temps down here are around 85 to 90 degress. I just pulled the water pump out and put a new merc in. I didn't see anything wrong with the old pump but Im going to take it out this weekend and see what happens

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

I took my boat out over the weekend and im still having the same overheat problem. I did put a new poppet valve (just the RUBBER DIAPHAM) my mechanic said I didn't need the kit but Im thinking I do because with all the research ive been doing everything seems to be leading to the poppet valve. I did a temp laser test on the motor at idle and all was good no hot spots and the temp gauge in the boat is accurate. Also I pulled the spark plugs out they all looked normal with no signs of a head gasket issue. Im stumped!! What do you guys think? THANKS

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

I just did a laser temp test on the engine block and heads I didn't find any hot spots at idle and also the temp gauge in the boat is dead on. At idle the temps on the block and heads were all about the same between 125-130. Im stumped:grumpy:

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

anyone?

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

I also just tried lowering the motor down 1 inch on the transom still runs at 180 full throttle also i put the stock 17 pitch prop back on it and no difference. Im starting to think 180 degrees is normal temp for this motor especially with 85 degree water temperatures. But IDK

 

[Chris1956]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

Of course water boils ar 212*F, so the motor alarm would need to come on before that. 190*F sounds about right for the alarm.

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

my seloc mercury manual says that the warning alarm should turn on at 232-248 degrees and turn off at 195. Does this sound right? The temp sending unit measures the temp of the head not the water THANKS

 

[Chris1956]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

I think the guys at Seloc were drinking their lunch, when they wrote that. Motor thermostats are normally about 140*.

 

[Dukedog]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

How much "run" time on tha pump? Sometimes even tha OEM stuff won't last very long. We always replace tha complete pump first with an overheat problem no mater what unless its something else that's very obvious. Put "complete" T-stats (143's) back in it. I hear 'bout tha water temp tha boat is runnin' in will make a difference in motor temp but have yet ta figure out "how". Might make it warm up or cool down "quicker" but think that's all. Alarm is usually around 240 like they said. "Sometimes" Seloc gets it right! Tha very early (first generation V6) motors alarmed at 190 but not tha later models. Sounds like tha water isn't stayin' in tha block long enough. Could be volume of water being pumped, T-stat or poppet problem...........Seems like none of these parts (unlike most Merc parts) are that expensive compared ta end results............ jmo

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

I already had new tstats in it and it was running hotter upwards of 210 and still no alarm since i pulled them out ive been running 180 only at full throttle (it runs 150 160 at part throttle and 130 at idle. The water pump kit and poppet valve are brand new (had the same problem with other waterpump that was only 3 months old). When I pulled the other pump out it was like new.

 

[Dukedog]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

Sounds like ya covered all tha bases with those parts. Still sounds like its "leavin' tha block to quick....Pressure gauge? Water "pressures" at different rpm?............Might make ya lean towards power head and/or exhaust adapter plate gasket (between tha two plates). This is a reach but ya might peek at tha piston tops for any kinda "steam" wash. Will be very small if present. This may/may not indicate a small leak in divider plate/gasket. Have seen these develop a tiny crack. This doesn't change tha pressures but will cause a raise in temp and may not be enough ta cause tha cylinder ta "not fire". You did say this excess heat is a new problem, right?

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

I dont have a pressure gauge but i was thinking about installing one. My exhaust baffle came loose (the 2 nuts that hold it on fell off and went missing) My mechanic could only get one nut back on. I did notice the motor was alot louder when the baffle was off but since we put it back up its alot quieter. Could that cause the overheating?

 

[Dukedog]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

No, not really. I've seen motors come in for a water pump and tha tuner layin' in tha bottom of tha can. Pressure gauge is really a must when ya lookin' for an unknown coolin' problem. Did he pull tha power head ta fix tha tuner?

Re-read! Baffle? What are you referring too?

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

My mechanic called it the baffle it a piece about 1 to 2ft long located in the mid section. Ill get a pressure gauge. Where on the motor do I
mount or t off the line that would go to a pressure gauge? Thanks for you replies!!

 

[Dukedog]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

Ok. Tuner. 4 nuts hold it on. Did he pull pwer head ta fix? There is hose on top, right behind tha flywheel. "T" inta that hose on top....

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

No we didnt pull the power head to much work and I cant afford to pay him for that job. There was only 2 big nuts that were holding the tuner on (one on each side) I saw them myself. Hopefully I can get a pressure gauge next week. Thanks for the help

 

[merc150]

Re: 2003 mercury 150 saltwater carb motor running hot at full speed...HELP

Do I put the t fitting in the hose that connects the 2 thermastats? THANKS!