1987 150 COOLING

T

TAF

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JUST BOUGHT A 1987 MERC 150, SER # OA181592. THE TELL TALE IS VERY STRONG, CAN I ASSUME THE WATER PUMP IS OK? HOWEVER THE TELL TALE WATER SEEMS HOT. IF I UNDERSTAND CORRECTLY, THE TELL TALE IS THE LAST THING IN THE COOLING FLOW. HOW HOT SHOULD THIS GET, 140 DEG? (POST T-STAT TEMP). IF IT IS HOTTER THAN SAY 140 DEG WHAT SHOULD I LOOK FOR AS THE CULPRIT?
 
T

TAF

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Re: 1987 150 COOLING

FORGOT TO MENTION, THERE IS NO TEMP GUAGE, WATER PRESSURE GUAGE, OR OVERHEAT ALARM. ALL I HAVE TO GOBY IS THE TELL TALE.
 
K

KCLOST

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Re: 1987 150 COOLING

If you call Mercury, they will tell you 140-145F, but it's common knowledge that these motors (black max's) like to run hotter than most others....<br /><br />A good tell-tail is a good sign, obviously showing you that you are getting enough water up to the block. But since you just bought the motor, I would recommend changing the t-stats, poppet valve and water pump impeller. Start fresh and know where you are at..<br /><br />If you run the engine of the muffs (garden hose), at idle the water out of the tell-tail should be just warm, you should be able to take the heat easily. That is what mine is like anyway when the t-stats aren't opened fully yet. At full throttle or just after, that is another story, I would guess that it is much hotter, so hot I can't hold my hand on it....But I've never tried it... Get that overheat alarm fixed or install one... That will tell you if you have a problem with the block temperature...<br />I think your overheat sensor should measure metal temp, not water by the way...
 
J

JohnnyS

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Dec 30, 2002
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Re: 1987 150 COOLING

Had a similar problem with my 87' 150. Even though I had water coming out the tell-tale pretty good, the water got VERY hot and the overheat alarm would go off. <br /><br />What are the water pressure readings like? When I had the problem, the pressure rarely went above 10psi. Since I bought it used, I had nothing to base it on.<br /><br />Replaced water pump, t-stats, poppet - still had the problem. <br /><br />Mechanic finally flushed out the cooling system with 'some acid'. A bunch of 'stuff' came out. After that, the water pressure reading on the gauge went way up and varied nicely according to the RPM. <br /><br />Problem solved.<br /><br />Good Luck <br />John
 
K

KCLOST

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Re: 1987 150 COOLING

With a good tell tail low water pressure doesn't make sense... Unless you have a blockage near the temp/overheat sensor or at the water pressure fitting..... Since you don't have a pressure guage, the best way to start is to replace the basics as I mentioned above... IF it is indeed too hot, this could be a number of things, stats, impeller, a bad head gasket, and possibly a blockage in the water jacket. But don't flush the engine with any acid stuff, as it could get into the cylinders if you have a bad head gasket, and then you will have a big problem...<br /><br />You need to get that overheat sensor installed and working properly. <br /><br />By the way, what type of temps are you getting out of the tell-tail. Do you think you're having a problem, or just curious? What is the temp. at idle?
 
T

TAF

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Re: 1987 150 COOLING

I'M NOT TOO SURE WHAT THE ACTUAL TEMP OF THE TELL TALE IS. I WAS THINKING OF GETTING A CANDY THERMOMETER OR SOMETHING TO GET THE TEMP. THE OVERHEAT ALARM IS THE BELL-LOOKING THING UNDER THE CONSOLE, RIGHT? MINE IS WRAPPED IN A PLASTIC MESH TYPE STUFF. WHEN I TURN ON THE IGNITION I DON'T GET ANY AUDIBLE WARNING OR ALARMS. OIL INJECTION HAS BEEN DISABLED. HOW DO I TEST THE WARNING HORN ITSELF? WHERE ON THE BLOCK DO I LOOK FOR THE SENSOR/SENDING UNIT?
 
1

1986mariner150

Petty Officer 2nd Class
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Mar 13, 2004
Messages
142
Re: 1987 150 COOLING

That alarm beeper just has 2 wires and it gets 12 vdc to sound off. You can put a light or any noise maker that works on 12 vdc. I use a bright courtesy type light mounted just under the lip of the console.
 
K

KCLOST

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Re: 1987 150 COOLING

Fagro, yes that is the horn under the console.<br /><br />You can test the alarm easily by gounding out the lead wire that goes to the sensor, to the block. The sensor goes into the cylinder head just below the #1 or #2 cylinders (top cylinders).<br /><br />Do this with the ingnition key in the on position. I don't know if you have any exposed wire or metal at the sensor, but if you do, just use a scrap piece of wire and run it from the metal exposed, to ground on the engine.... If you have a hard time finding exposed metal on the sensor lead, track it back to the juction where it connects to engine with a screw (it's above the rectifier somewhere) and ground the junction... <br />Let me know if you have any problems...<br />It probably works, as my oil injection is disabled also and I get no test beeps when turning the key on either. But my overheat sensor/alarm, is still working.
 
T

TAF

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Re: 1987 150 COOLING

THANKS KCLOST.<br />TODAY I PLAYED WITH IT A LITTLE. I GOT THE HORN/ALARM TO SOUND IF I GROUNDED THE TAN WIRE TO THE ENGINE BLOCK WITH THE IGNITION ON. I GOT NO SOUND WHEN I CONNECT IT BACK TO THE TEMP SENSOR WIRE AT THE JUNCTION BLOCK NEAR THE STARTER.<br />HOW IS THE ALARM SUPPOSE TO WORK?,HOW CAN I TEST THE SENSOR? IT LOOKS LIKE JUST A WIRE THAT GOES INTO THE BLOCK AND IS SEALED WITH RTV OR SOMETHING.<br />IF I UNDERSTAND CORRECTLY, WHEN YOU TURN ON THE KEY IT SOUNDS TO LET YOU KNOW IT IS WORKING. I GET NOTHING WHEN I TURN THE KEY, UNLESS OF COURSE I GROUND THAT TAN WIRE AT THE SENSOR LEAD.<br />ANY IDEAS? HINTS? SUGGESTIONS?
 
K

KCLOST

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Re: 1987 150 COOLING

Ok,<br /><br />The overheat sensor wire should be black, with possibly a piece of clear tubing around it... The temp sensor wire (coming from the other block) will be a white wire (possibly discolored to a tan) WITH a blue stripe.... The black wire goes to the screw/junciton I mentioned, and the white w/blue stripe wire goes directly to the temp guage.<br /><br /><br />The overheat sensor is designed to ground out to the block if the temp reaches 240F. <br />As far as the testing beep goes, when you turn the ignition key, it's probably been disabled due to the removal of your oil injection system... I think the testing signals for both the oil injection and overheat run in conjunction with each other... My motor has no testing beeps anymore either... I could be wrong but I believe yours has been disabled....<br />The key factor for you is to make sure that when the overheat sensor is grounded the alarm will sound. And based on your tests it does, GOOD NEWS.... That screw that connects the overheat lead to that junction, may have paint on it so loosen it up and retest, ensuring you have good metal contact. Again, grounding the lead (basically) to engine ground.<br /><br />You can remove the overheat sensor, by unscrewing a couple of bolts that hold a bracket on around the sensor and then pull it out.. But I don't know how to tell anything about it's condition after you do...
 
T

TAF

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Mar 1, 2004
Messages
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Re: 1987 150 COOLING

THANKS FOR YOUR INFO. MINE DOESNT HAVE A TEMP SENSOR OR TEMP GUAGE. I JUST HAVE THE OVERHEAT SENSOR. THE ONE YOU MENTIONED WITH THE CLEAR PLASTIC TUBING AROUND IT. IT IS LOCATED JUST BELOW THE #1 CYLINDER. THIS "SENSOR" DOES NOT LOOK SERVICEABLE. THE BLACK LEAD GOES RIGHT INTO THE HEAD, AND IS SEALED WITH SOME RTV/SILICONE STUFF. NO BOLTS, SCREWS, ETC. IS THIS HOW YOUR OVERHEAT SENSOR IS?<br />THIS BLACK LEAD GOES TO A PLASTIC JUNCTION BLOCK AND JOINS WITH THE TAN WIRE FOR THE ALARM.
 
S

strut70

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May 25, 2004
Messages
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Re: 1987 150 COOLING

I have the same problem with my 150 merc...if you are facing the engine from the back. there are two sensors... the one on the left goes directly to the temp gauge....i cannot get it to sound the alarm by shorting it out...the one on the right that has that is mounted in rtv or whatever will sound the alam if shorted out ......not sure why one will check ok and the other won't........My motor sounds like the typical 80's merc stays cool at low or mid rpm,s at wot the temp gauge goes almost to the redline.. but never has set off the alam......so makes me wonder about the alarm.<br /><br />It does do the check ok when you turn on the key and all the oil alarms work ok......had a low voltage problem with the oil alarms but swithced the green wire from alarm box to another coil and solved that problem......any idea,s why the one sensor is not going off when i short it out??????
 
K

KCLOST

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Jun 22, 2002
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2,095
Re: 1987 150 COOLING

Your temp. sender isn't connected to the horn. So it won't go off if you ground it... Unless you ground it to the overheat lead where it connects to the wire junction just above the switchboxes. In that case you are just grounding the overheat sensor..<br /><br />By the way, when I run WOT my guage hit's the redline (or almost does) also... We have the blackmax's which are known to run pretty warm. I haven't had an overheat yet either (knock on wood)..
 
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