1986 Mariner 150HP Cooling Issues, PLEASE HELP!!!

[dropnbassonu]

Hi,

So here's my dilemma. I crank my boat up and my alarm runs for what seems to be no set time. Sometimes its 1 minute, sometimes its 5 or 10 minutes. Here is the problem.....

My boat will idle fine up to about 3-5 mph and the temperature gauge won't go up, it stays in the middle. As soon as I drop the throttle and gun it, the temperature gauge goes up to hot. My dad and I replaced the water pump impeller, even though it turned out the one in there was basically brand new. It was and has always peed a nice stream out of the boat, even at full throttle. So, my next thought was maybe a thermostat. I took out both thermostats today and ran it the same way. Same problem. Below is a pic of the thermostats....

Also, for what it's worth last time I took it out in the morning and idle'd the gauge was right in the middle. After pushing it a little (~15mph) it started going up to hot, but as soon as I gunned it and planed out the gauge went from hot to cold in a matter of seconds.

Could it just be the gauge or heat sensor?

Any other suggestions?

Thanks a ton!!!

 

[DamianJP]

Re: 1986 Mariner 150HP Cooling Issues, PLEASE HELP!!!

Hey dropnbassonu

I don't know if the thermos came out like that but 1 thermo gasket is up side down. The right thermo is the right orientation. But get new thermostats and make sure the gaskets are installed like the right one in the picture.


Thermos stuck open will overheat at idle.

Poppet controls water flow at high RPM.

Now when you said you gunned it the first time it overheated.
Then next time you gunned it, it cooled in seconds.
Mabey something like the poppet is sticking here and there. When is the last time you've done the poppet?



Now about the gauge and sender...

Im away from my home right now and only have 1 service manual in front of me, which covers 1990-2000 2.5-275 Mercs.

Sender,
When temp reaches 232-248 F(Heat range might be diffrent on your engine!) the switch is closed. During normal operation switch is open.

Place switch end into water with a thermometer and heat to 232-248 F.

Take switch out and as it cools,perform an Ohms test to check when the switch resets.

If switch does not meet spec (or change in Ohms) as it cools, replace send unit.


Gauge

Hook up Pos from battery to the "I" or ignition post
Hook up Neg on "G" or ground post
Gauge should pin to lowest spot.

Hook up Pos from battery to the "I" Post
Hook up Neg from battery to the "G" post
Now jumper the "G" post to the "S" sender post.
Gauge should pin to highest spot.

If not the gauge is defective and need to be replaced.


Lemme know what ya find and if ya need more help.


DamianJP

 

[dropnbassonu]

Re: 1986 Mariner 150HP Cooling Issues, PLEASE HELP!!!

OK, I haven't taken my boat out much lately, but I think the poppet valve needs replacing. I can go along under 3000 rpm's without any overheating issues, but as soon as I get over that the temperature gauge starts to go up.

My question is, do I need to buy the whole valve kit? Will I need all of these parts?
http://www.amazon.com/POPPET-VALVE-GLM-Part-Number/dp/B004AQYY84/ref=sr_1_2?ie=UTF8&s=sporting-goods&qid=1291049216&sr=8-2

Thanks!

 

[RadarRick]

Re: 1986 Mariner 150HP Cooling Issues, PLEASE HELP!!!

Damian,

To test the sender, you recommended placing the switch end in water and heating to 232. The problem is that water boils at 212 so I don't think you can go any higher.

Perhaps one could put the switch end in an oven and use oven thermometer to monitor temp?

 

[CharlieB]

Re: 1986 Mariner 150HP Cooling Issues, PLEASE HELP!!!

Engine temp should never be anywhere near 212.

A water PRESSURE gauge is far more reliable in determining a heating issue and provides a constant gauge of water pump performance.

Heating at higher speeds can be caused by a number of things;

restricted fuel supply, deteriorated water pump/impeller, gasket leak(s), head, exhaust, or powerhead base gasket, improper ignition timing, dirty carb jet(s)

Careful inspection and testing of ALL components will reveal the problem BEFORE resorting to throwing money/parts at the motor.

 

[dropnbassonu]

Re: 1986 Mariner 150HP Cooling Issues, PLEASE HELP!!!

Engine temp should never be anywhere near 212.

A water PRESSURE gauge is far more reliable in determining a heating issue and provides a constant gauge of water pump performance.

Heating at higher speeds can be caused by a number of things;

restricted fuel supply, deteriorated water pump/impeller, gasket leak(s), head, exhaust, or powerhead base gasket, improper ignition timing, dirty carb jet(s)

Careful inspection and testing of ALL components will reveal the problem BEFORE resorting to throwing money/parts at the motor.

I agree 100% with you, the only problem is I am clueless when it comes to checking/inspecting these things. I guess I'll have to resort to my least favorite option, taking it to the boat mechanic, who I know will bend me over...

 

[CharlieB]

Re: 1986 Mariner 150HP Cooling Issues, PLEASE HELP!!!

You don't necessarily have to take it in just yet. You can start checking a bit deeper. You have already replaced the impeller, now start looking at water FLOW.

Fire the motor with the T-stat housings removed, you should see water out both openings at an idle proving the water pump is moving good flow.

Reinstall new stats, fire the motor and allow to warm up, watch the P stream to ensure a strong flow once the stats open.

On the water when the motor begins to heat, how is the P stream? Strong, weak, none, just steam?

If the P steam disappears then it is an indication of NO water supply at speed while under load, often caused by a head gasket leaking combustion gases at HIGH pressure into the cooling system, overcoming the water pump pressure. The high pressure gases effectively stop any water flow thru the motor and it overheats. This test MUST BE done under load as cyl pressure will NOT raise this high just reving the motor in Neutral, the prop MUST be in the water and doing work.

If there is steam instead of water from the P tube then remove the cyl heads, check all surfaces for straightness, and install new gaskets.

 

[dropnbassonu]

Re: 1986 Mariner 150HP Cooling Issues, PLEASE HELP!!!

You don't necessarily have to take it in just yet. You can start checking a bit deeper. You have already replaced the impeller, now start looking at water FLOW.

Fire the motor with the T-stat housings removed, you should see water out both openings at an idle proving the water pump is moving good flow.

Reinstall new stats, fire the motor and allow to warm up, watch the P stream to ensure a strong flow once the stats open.

On the water when the motor begins to heat, how is the P stream? Strong, weak, none, just steam?

If the P steam disappears then it is an indication of NO water supply at speed while under load, often caused by a head gasket leaking combustion gases at HIGH pressure into the cooling system, overcoming the water pump pressure. The high pressure gases effectively stop any water flow thru the motor and it overheats. This test MUST BE done under load as cyl pressure will NOT raise this high just reving the motor in Neutral, the prop MUST be in the water and doing work.

If there is steam instead of water from the P tube then remove the cyl heads, check all surfaces for straightness, and install new gaskets.

Thanks for your help! I have taken my boat out with and without the thermostats and the stream at all rpm's is nice and steady. I haven't noticed any steam coming out, though the motor does get hot enough that I can only hold my finger on it for maybe 1-2 seconds before it starts to burn.

 

[Dukedog]

Re: 1986 Mariner 150HP Cooling Issues, PLEASE HELP!!!

Just something we do on older motors that develope coolin' problems. We don't do it one part at a time ta start with. Its ALL old!

Replace COMPLETE waterpump and gaskets.(no mater how good it looks)
New T-stats, rubbers.
New poppet assy, gaskets.
Use ALL OEM parts in tha coolin' system.

This is tha COOLIN' SYSTEM. I consider it tha most important part of any Merc/Mariner.............

An older motor probably needs this stuff anyway. This is not all that expensive ta do ta keep your motor in good health compared to screwin' up tha powerhead chasin' tha problem.

This resolves tha problem in 90% of heatin' problems. If it doesn't, your gonna need a lot more knowledge of how these motors work than most askin' questions on tha computer............JMO and good luck.

Oh yeah, get a water pressure guage first............

 

[CharlieB]

Re: 1986 Mariner 150HP Cooling Issues, PLEASE HELP!!!

Hot water alone is not necessarily a head gasket.

Pay attention to what has already been posted, check to ensure the poppet valve is in good shape, the seat is firmly in the block and not sliding out with the valve as it opens.

Check engine timing and the link'synch to throttle opening, throttle pick-up either too early or too late can also cause heating.