XR6 still running hot still cant firgure it out

[merc150]

Hope you guys can help me figure this out! I have a 2003 merc 150 xr6 CARB motor. I changed the thermostats,poppet valve,temp sensor for the gauge, new water pressure and temp gauges,spark plugs (yes they are the correct ones) and did a complete water pump kit, all parts are from mercury, (also back flushed the cooling system with a water hose and found nothing),inside of the heads look clean. I also rinse the motor with salt-away everytime and after every use. I had the cooling issue before I did all this work also my compression is 125 in a 6 cylinders. The motor seems to run hotter at lower speeds but will slowly cool to 190 or so at WOT. At slow speeds the motor will get close to 200 degrees before I turn it off (seems like it will just keep getting hotter). My water pressure is good (3-5 at idle and 11-13 WOT). I also went from a 19p prop to a 15p prop and that didnt help any (Stiletto props). I looked at the water holes in the lower unit and they are clean. The motor is mounted at the correct hight on the transom. Im in florida and right now the water temps are 90 degrees.I was thinking maybe the timing is off but looking at the timing screw it doesnt look like anybody has messed with it (factory paint is still alined on the screw). The motor runs absolutely perfect except for this cooling issue. I also used a laser temp gauge just to make sure my gauge was right and it is. ANY help would greatly be appreciated!!! I need to get this fixed ASAP I have tournaments coming up. THANKS

 

[merc150]

Also the sparks plugs are clean, light brown and dry

 

[Chris1956]

A slow RPM cooling issue candidate is the waterpump. Sometimes the pump base will melt a bit. Did you replace the waterpump base, base gasket, wearplate and it's two gaskets, the impeller and the water pump cover? When I have had that issue, the impeller fins had small missing pieces of rubber where they touched the wearplate.

 

[merc150]

I replaced the base, base gasket, wearplate and the gaskets. Also when I took the old stuff out including the impeller it all look good as it was all replaced last year

 

[merc150]

Im out of ideas lol. Anybody else running half way on the temp gauge? Im starting to wounder if this is normal. My seloc manual says the over heat alarm is set to off at 230 degrees and back off at 195 (I get up to 190-200). Also I tested my alarm and it works but has never gone off

 

[wired247]

I'd pull the poppet cover and make sure your rubber base washer isnt blown out.

 

[merc150]

I just put a new poppet valve kit in it...still does it

 

[wired247]

Try the merc# 14586 thermostats used in the 225 promax's. They open at 120 instead of 143 and I think open wider too. The Sierra number is 18-3549.

 

[merc150]

Ok ill order them now! I appreciate your help

 

[merc150]

What about if I gut my thermostats?

 

[wired247]

You wouldn't maintain an even water temperature if you did. I have seen all kinds of stuff about thermostats like if the water passes through the block to quickly the engine will overheat because it doesn't have time to pick up the heat. Sounds like a load of horse crap to me though as every experience I've ever had with no thermostats is that the motor never gets to operating temp. The thermostats are there to keep the motor at an even operating temp . Without them the motor will stay too cold which is as bad or worse than running moderately too hot.

If you have good water pressure and you don't have blown head gaskets theres not too many other things it could be. Its not a very complicated cooling system. Thermostats, a pressure relief valve and a pump. You have pressure so the pump isnt in question and you arent going over or under pressure so the poppets probably OK.

One of the issues with the Merc V6 cooling system is that is NOT a full flow system. The thermostats dont get all the water. Most of it dumps out the exhaust and isnt regulated by the thermostats or at least doesnt go through the temp regulation system the thermostats provide. I run the pro max thermostats and my cruise temp is minimum 120 ish but it will go as high as 170 or maybe a bit higher after a long 7K run and I stop to idle for a few minuted and the pistons dump their heat in the cooling system . You might also want to look at your jetting. Are you running lean?

 

[merc150]

didnt plan on taking the thermostats completely out just cutting the spring out and putting just the top of the therm back in just to restrict the flow. We do it on our race cars but woundering how it would do on a outboard. Thanks for the fast response!

 

[wired247]

Where is your sender for the gauge located and how hot is your tell tale water?

 

[merc150]

sender is under the number 1 spark plug. tell tale seems pretty hot but not a steamy hot but feels kinda normal to me

 

[wired247]

If your water temp isnt 180+ I would question it actually overheating and I'd be looking more at the gauge or sender unit. What type of sender are you using? Is it screwed into the dry NPT port on the back of the head?

 

[merc150]

just put a new mercury sending unit in and a new gauge and the sending unit sits in the head and theres a fork type bracket holding it in and the actual bolt goes in the head. I also used a new laser temp gun pointed it at each cylinder while running it on the muffs and it was reading the same as the gauge. With the motor idling out of the water with the muffs on my temp stays at 160

 

[merc150]

I took the hose off that connects the 2 thermostats and replaced it with a clear hose im going to run the motor on muffs in a few hours to see if theres any air getting in the water

 

[Dukedog]

Sensor under # one is over heat buzzer only. Won't work for a gauge. Where are ya pickin' up tha sender connection for tha gauge? If your not gettin' an over heat alarm wouldn't worry 'bout it unless ya changed something up front. Know several that run 3/8" hole washers in summer with no problems. Tha 143's should be just fine. If not ya got other problems. Don't know where he gets lower temp for tha PM. They ALL come with 143's from production........Just like yours.

 

[wired247]

Offshore mid and 15 " mid section 225 pro max's came with the 14586 thermostats. My heads were takeoffs from a new 1998 225 promax offshore and thats what mother Mercury put in there.

 

[Dukedog]

My mistake. Tha 15" 0ffshore PM is actually tha only "little" V6 that did. Production or Hi Performance. Its tha only PM that had a one piece adapter plate, offshore housing. Very few of those were sold........Still if it over heats with 143's he's got problems elsewhere........