9.8 Mercury Overheating

[Jwill]

My 1982 Mercury 9.8 outboard seems to be overheating.<br />I recently bought the motor and don't have much history on it. <br />I am currently running it in a barrel and not yet have run it on the water yet.<br />The outboard runs perfect but the water coming out the pee hole goes from cold to hot in about 45 seconds. The water coming out the pee hole isn't shooting out that hard. It will shoot out for a second then it will sputter then shoot, etc.<br />The water pump is brand new. <br />I checked the thermostat and it was missing so evidently someone took it out because it was bad or the motor was getting hot on them.<br />The water in the barrell is cold the entire time I'm running it. <br />I ran it with the thermostat housing off and the water boiled out of it ok. Is the water suppose to shoot straight up when the cover is off?<br />Any advice is appreciated.<br />Thanks!!!!

 

[jim dozier]

Re: 9.8 Mercury Overheating

Before you do anything else make sure the water level in the barrel is above the location of the water pump impeller (not just the inlet hole) these pumps don't suck they push water.

 

[Chinewalker]

Re: 9.8 Mercury Overheating

It's possible the pisser tube is simply partially blocked or crimped. It should be a solid stream out the tube. If you're getting a good flow at the t-stat housing, it should come out the pisser good & strong...<br />- Scott

 

[Jwill]

Re: 9.8 Mercury Overheating

The impellar is probably a foot under water so thats not the problem. <br />The water is boiling out of the T-stat housing but is it suppose to be shooting out?<br />I'm going to purge the water line with compressed air to see if that helps.<br />I'll post with the results.<br />Thanks!!!

 

[jim dozier]

Re: 9.8 Mercury Overheating

You probably don't want to hear this but I would recommend pulling the lower unit off again. Clamp a garden hose onto the water pickup tube that comes out of the water pump and flush the sysem with the thermo cover off. Then backflush it with the hose from the thermo cover down. Check the grommet at the top of the water tube to see if it is fouled and blocking flow. Somebody probably removed that thermostat in a vain attempt to fix an overheating engine before you got it. You said you fixed the pump now you have to rule out other blockages. If this doesn't get it, you may have to remove the head. Hope not.

 

[Bear]

Re: 9.8 Mercury Overheating

Thermostat missing? Hmm, it still acts like my '87 Mercury 8 HP. I thought it was time for a new impeller (the seller said it was done the year before). I checked old post here and found out that it was normal for Mercury. My old Mercury 402 didn't pee like that (weak/strong and hot/cold) or my Honda or any other ob I had seen so far.<br />Check these (yes I had to check old posts again )<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=17;t=003180 <br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=17;t=005846 <br /><br />Now, how come if you don't have a thermostat?

 

[Bear]

Re: 9.8 Mercury Overheating

Check this picture<br />#31 M75692 1 THERMOSTAT-143<br />9.8 HP 1979-1985 serial number 5206550 and up USA <br /> http://www.boaterssupply.com/images/fiche/big/mrmn17.GIF <br /><br />I think you should get one to keep the temperature under control.<br /><br />BTW I used my 8 HP for a few months last year and the temperature was no problem. I can hold my hand on the powerhead long enough to tell.

 

[Jwill]

Re: 9.8 Mercury Overheating

According to the message archives there's nothing wrong with the motor. <br />I ran the water line in a jug and put a meat thermometer to read the temp. The lowest reading on the thermometer is 140 degrees and it never got close to that. I'm guessing the water temp is about 120 degrees max.<br />I guess the sputtering water out the pee hole is fine according to the archives.<br />I thought for sure there was a problem because my Johnson 25 shoots water fast even with a 10+ year impellar in it. And the water it shoots out is just warm to the touch.<br />I checked the compression in the Mercury 9.8 and it only read 90-95 psi. Is that kinda low or is there still alot of life left in the thing???<br />My Johnson which is about the same age reads 115-120 psi. <br />Thanks to everyone who posted and I would be interested in knowing if the compression is low or not in the Merk.<br />Thank You!!!