135 blackmax mercury overheating

[wakeup]

I have a 1988-89 merc 135hp Blackmax that I think may be running too hot at high revs. It runs at approx halfway on the temp guage at low revs and idle, however when I tow skiers at high speed the temp guage goes up to three quarters or higher. If I throttle back off the temp comes straight back down. The tell tale out the back of the motor is good and strong with a constant pressure...any ideas would be much appreciated

 

[rodbolt]

Re: 135 blackmax mercury overheating

hello<br /> have you checked the t-stats. if your pulling skiers then you must maintain the system. that means a yearly water pump kit a yearly set of t-stats. I use the sierra ones with a steam vent that are self flusing and a pressure relief valve cleaning and diaphram replacement.<br /> good luck and keep posting

 

[KCLOST]

Re: 135 blackmax mercury overheating

Wakeup,<br /><br />You have the classic signs of a normal Mercury V6 of that decade.<br /><br />Mine, does the same thing. At WOT the guage nearly (or does) read at the max. And I'm not pulling skiers...<br /><br />Your temp. sensor is measuring the metal temperature of the head not water temp. I truely believe your readings are normal. It is wise however to check the stats and the pressure relief (poppet) valve just to be sure. But I would almost bet my boat that you are OK... There have been many topics just like yours and as long as your not getting an overheat alarm you shouldn't have anything to worry about.. These Mercs like to run hot!

 

[bluebyyou]

Re: 135 blackmax mercury overheating

Well just to muddy the waters...I have the exact same engine and my motor does just the reverse. Cool at WOT and hot at mid-range! It's in the shop right now getting the waterpump and impeller done.

 

[KCLOST]

Re: 135 blackmax mercury overheating

BBY,<br /><br />Does it always do that or just recently...<br /><br />It sounds like your temp sensor is measuring water temp, not metal... <br />Just curious...

 

[Reel Precision]

Re: 135 blackmax mercury overheating

I agree with KCLOFT check your poppet valves.