1988 Mercury 175 - Running Tempature

[jkering66]

I have a 1988 Mercury 175 outboard that appears to slowly heat up at headway speed, when you just click into forwared and stay at that speed for 10/15 minutes. It appears to top out at a little under the 3/4 mark on the temp gauge, no numbers on the temp gauge. Whe I get the RPM up to 1800 the engine cools right down to under 1/4 on the temp gauge. It has a new water pump. When I run at 4k or 5k RPM it is right under 1/2 on temp gauge.<br /><br />Is this normal for a Mercury outboard? <br />Should it heat up that much at 1100 RPM in forward?<br /><br />Any information would be appreciated.<br /><br />Thanks

 

[gss036]

Re: 1988 Mercury 175 - Running Tempature

I run a 1989 Mercury 200 hp and my temp stays steady, usually at about 150 degrees. Might be time for a new water pump / rebuild. You might have an obstruction somewhere also.

 

[KennyKenCan]

Re: 1988 Mercury 175 - Running Tempature

Jack,<br /><br />That is considered normal operation.<br /><br />Running at or slightly above idle, in gear will cause the temp to rise because the pop-off valve has not opened and the engine is running its cooling water thru the thermostats only.<br /><br />Once you gain enough RPM and water pressure, the pop-off valve will open and the temp should go down to normal, 143 degrees.<br /><br />Also, once the body of water you are boating in temerature goes above 80 degrees, you can expect that normal operating temp of 143 degrees to be higher, but your temp should never exceed 165 degrees, or go into the red zone of the gauge.<br /><br />Heres another tip, get rid of that gauge without numbers, not only is it annoying, it doen't tell you alot of information.<br /><br />Get a gauge that has numbers on it, I use one for an I/O.<br /><br />Hope that helps.<br /><br />Kenny

 

[nilsson]

Re: 1988 Mercury 175 - Running Tempature

Hi Jack66<br /><br />Kennykencan is right, what youre seeing is normal. <br />I own the 135hp version of your motor with the boat equipped with the same un-numbered Quicksilver gauge.<br />After buying the rig, I replaced waterpump, thermostats and pressure cont valve- same temp reading <br />Had it looked at by reputable Merc mech who checked the whole cooling system.<br />The reason for the wild variation in your gauge is the fact that your motor uses an UNREGULATED alternator, the high volts at high rpm sends your gauge higher than normal.<br />The trick?- fitted a 12V stabiliser, from a hobby store, to gauge "+" ign. input. Gauge now reads between 1/4 and 1/2.<br />Your motor sounds fine, but get it checked first- all those whizzing pistons, rods and bearings all clock up the dollars when seized!! <br /><br />good luck<br />Nilsson

 

[jkering66]

Re: 1988 Mercury 175 - Running Tempature

Thanks guys, good information. I will get a temp. gauge with numbers. The engine does have new water pump and thermostat.<br /><br />I have owned I/O's in the past and did not notice a big temp swing based on RPM, so I was not sure on the outboard.<br /><br />On a non numbered temp. gauge, is there a general temperature rule of thumb that I can go by, ie. 1/4=100 degrees, 1/2=150, 3/4=200?<br /><br />I am curious what this engine heats up to when running at low RPM.<br /><br />Thanks again for the reply's.