Question for all the experts......

[KCLOST]

Based on my searches there are a lot of questions that have come up on high temp problems with the 1980-90 models mercury's.... Specifically in the 135-200 hp range... Anyway I know of several posters that have battled with this problem, replacing water pumps, stats, poppets, head gaskets, etc. Most of the time without any signifigant improvements... <br />I called Mercury today and asked them what the proper Full Thottle temp should be for my 86' Merc. 175hp... And after the lady put me on hold for 20+ minutes finally she said that the temp should be between 140 to 145F... That IMO is a bunch of BS since the stats open at almost that exact temp, after she told me so eirlier... <br />I'm having what I feel is a high temp. problem, since my temp gauge reads almost to the max a full throttle... Granted, I haven't confirmed the temp, but I would really like to hear your best opinion on the normal operating temp on these series of motors... I think it would help a lot of people out....<br /><br />Thanks..

 

[Skinsk]

Re: Question for all the experts......

I'd check the temp on the motor first. Are you getting an overheat alarm? <br /><br />I personally dont' think that Outboard temp sensors are accurate at all. The merc guy at school said that he puts a peice of cardboard down the hole before he put the sensor in because they all read hot. (I don't reccomend this of course, but it's to prove a point)<br /><br />If it overheats at WOT, then it may very well be poppet problem.. Such as the poppet sticking shut.<br /><br />Scott.

 

[trumanlake]

Re: Question for all the experts......

kclost, I have a question(s) for you. Where is your temp sensor that you are using located, and what type of heads (type 1 or 2)? There is a reason I am asking(to be explained later)<br />Thanks

 

[KCLOST]

Re: Question for all the experts......

I'm going to try to get a reading off of the head with a lazer this weekend...<br /><br />Skinsk, I really don't think its a poppet problem. I replaced the diaphram and clipped a loop on the spring last weekend (it wasn't stuck), replaced the water pump and stats.. Went out to the lake and the same thing happened... I have not had an overheat alarm, but I don't like the high temp issue... One thing that interests me is that when at full throttle the temp gauge reads almost to the max (at H). But when I throttle down it immediatly drops, I mean IMMEDIATLY... Is that normal? If its that hot wouldn't it take a little longer to cool down?<br /><br />Trumanlake,<br />I do know that the temp sender is right underneath the #2 cylinder (port or left side of the motor, top cylinder) the overheat sensor is on the other side... As far as what type of heads I have, I'm not sure of your quesiton (I guess I don't know what I have).<br />Does anyone know what the proper temp. should be a full throttle?

 

[trumanlake]

Re: Question for all the experts......

Ok, now for thew explaination. You are measuring the temperature in the same location that the overtemp thermal switch is just different side. The thermal switch will not close until it reaches 240 degrees. At this position, only a 1/4 inch or so directly in front of your sensor you have internal cylinder temps of 400 - 500 degrees. Your temp sensor is not in the water jacket. To be more accurate on temp, if you do not have a pressure gauge, install your temp sensor at the top-rear of the block. That will put you into the water. I would bet that if you measure the length of the overtemp sensor in the starboard side you will find it to be approx. 15 1/2 inches long. Check that and let me know.<br />Just for grins, do you ever come down to truman lake?

 

[KCLOST]

Re: Question for all the experts......

15-1/2" ?????<br /><br />Do you mean 1-1/2" ??<br /><br />Trumanlake, so you think that I should move it to where the pressure gauge normally is? (I don't have a pressure gauge on this motor)...<br />Surely I'm reading water temperature now, aren't I? That would explain why the temp drops so fast when I throttle down, wouldn't it?<br /><br />BTW, I haven't been down to Truman yet, but plan to very soon. Mostly do my fishing at Hillsdale, Smithville, Marion, and sometimes down at Bull Shoals where my parents live....

 

[trumanlake]

Re: Question for all the experts......

Sorry about that, was getting ahead of myself. I should have said measure the lead length of the sensor. oopps Your measuring the temp of the metal not the water.. There should be a brass plug at the top of the block. I myself with my 200 would like to have both water temp and pressure but, I stick with the pressure. I can tell exactly when the thermo's open and when the poppet opens just by looking at the pressure. If you have any questions email me if you want kaywilli@iland.net<br /> <br />Hook on to it and come on down, fish'n been pretty good.

 

[KCLOST]

Re: Question for all the experts......

The temp sensor is going into the water jacket cover on the cylinder head... Does it go all the way through the jacket and into the head?<br /><br />Regardless of where it goes, should it measure water temp or metal temp? And what should the proper temp be? <br /><br />And why do you suggest I measure the overheat sensor, since we are talking about the temp sonsor on the other side?

 

[KCLOST]

Re: Question for all the experts......

Ok, I think I figured the sensor thing out with some help from a friend of mine...<br />I have a type 1 head with an 18" overheat sensor. The Temp sender goes through a hole in the water jacket and touches the head. It does not enter the water...<br />What I really need to know is what the proper temp should be at full throttle with this type of sensor and its location. (right below the #2 cylinder).<br />Who's brave enough to answer that one?

 

[trumanlake]

Re: Question for all the experts......

I am really surprised that the lead length is 18 inches. Normally, according to the service manual if the temp sensor mounts under the spark plug hole it should be a 240 degree which would be 15 1/2 inches in length. The 18 inch normally mounts to the side of the head which would be a 190 degree. With that in mind I would assume (we all know what that stands for) that would be in the lower 200 degree range (210-230), which would still not be an accurate indication of the water temp. Cylinder temp will be dependent also on other factors, (octane,spark advance,proper oil ratio,.....) The black max's run right on the edge anyway. I would imagine that if you were to install the sensor in the block at the top, you would probably get readings in the 195-200 range. I have yet to see published the actual readings at WOT. I would imagine that all will vary slightly, even with identical motors. The reason I keep dwelling on the lead length is that the Mercury parts list is wrong, we found out. Anyone that his purchased a new sensor because the insulation on the old one was cracked and brittle will have received p/n 98799 (i believe that's it) which is the wrong one. With a little research in the old original manuals it will tell you which one is correct, and that's not it! I thought I had an over temp situation after I had totally rebuilt the block, the engine was just getting up to operating temps at 4 grand.

 

[KCLOST]

Re: Question for all the experts......

I was wrong truman, It is indeed 15-1/2"...<br /><br />Sorry for the mix up...<br />So you think I should be getting readings around 195-200 with my sensor?

 

[CU2NITE]

Re: Question for all the experts......

KCLOST,<br />Wow this post sounds way to familiar to me. I have an 85 150 Black Max and I have had the same problems with my heating getting up around 195-200 at full throttle, it stays in range at half throttle or under. I have checked compression 125 on all, changed impeller, water pump housing(upper and lower and all gaskets), stats, head gaskets, exsaust gaskets, checked and changed outside water jacket gaskets, checked all water passages, changed heat sensors, checked fuel system for "running lean", and rebuilt my poppet. DIDN'T CHANGE A THING!! Also my prop pitch is fine, I run 700rmp in gear and 5800rpm at full out, not to mention shes peeing like a champ. I think Trumanlake had the most concrete answer to your post. I think these motors must run warm. Anyone else out there have any suggestions before myself and KCLOST lose our marbles.<br />Thank you<br />CU<br /><br />-RUNNING THE MOTOR WHILE LISTENING TO THE HORN WILL MAKE YOU MORN!!!!!-

 

[The Marine Doctor]

Re: Question for all the experts......

I am going to take a shot at this. I believe the v6's during the 80's came with the old style waterpumps.<br /><br />impeller 89984T<br /><br />I do not think this high pressure Waterpump is capable of delivering enough water to cool these engines. <br /><br />With todays fuel engines run hotter than they used to.<br /><br />In the 90's they switched to pumps with a HIGH VOLUME rather than pressure and they did this with all their product...Maybe to compensate for the heat problems????<br /><br />TMD

 

[trumanlake]

Re: Question for all the experts......

Ok, keep this in mind. Again, what are you measuring with your temp sensors?? If on your trucks or cars you wanted to know what the engine temp was would you mount the sensor on the surface of the head or in the water jacket where it would be giving you a more accurate indication of the actual temperature??? Think about where Mercury put it and what they think is the danger zone on the type I head design (240 DEGREES)! Proper combustion is what they are after. Internal combustion temps below 400-500 degrees you're going to have problems on down the road. As for higher volumes, you still have the same size water tube going to the block, same size opening in the rubber grommet that holds the water tube, same size poppet opening to dump at higher rpm's. What have you really gained? At 4200-5800 rpm's 20-25 psi there is alot of water being run through. Turn around (carefully) and look what your dumping out the exhaust ports at the rear. <br />KC LOST, I'll send you a note I sent THE COL. last night.<br />I love it when you're just cruisin' along by a johnnyrude at 55mph then open her on up to 82mph (gps). Puts a smile on your face! Ya gotta believe in em'!!! #1 on the water for a reason!

 

[KCLOST]

Re: Question for all the experts......

So in theory, with my motor, my sensor, properly working stats and poppet, and assuming the temp sender is working correctly (measuring metal temp on the head)... Readings of 195-200 are pretty normal at WOT and not damaging to the engine...<br /><br />Thanks for all your help...

 

[trumanlake]

Re: Question for all the experts......

I believe you'll run with the best of them!!!!<br />If I were you though I would invest in a pressure gauge, not much of an investment but a whole lot of reassurance. Wouldn't be without one!<br />Come on down to the lake sometime, fishn's good.

 

[ronmold]

Re: Question for all the experts......

I wonder if the temperature gauge problems might have anything to do with the voltage reg. problems early mercs had. After all the temp sender is just a variable resistor and the guage inself runs off of the +12v rail. If your voltage rises to 15 - 16 wouldn't your sender pass more current showing a higher temp? Just a thought.

 

[trumanlake]

Re: Question for all the experts......

Now that's a thought. But, most electric gauges have internal regulators just for that reason, not all but some.<br />Thinking outside the box, I like that.