overheating on Merc 140?

[bobafett]

I have an 1986 Mercruiser 140 4 cyclinder with raw water cooled system Not in salt water environment. When I hook up garden hose to the lower unit and let it warm up, the temp reading on the dash is about 155-160 F at idle. Is this normal operating temp at idle? I unhooked the hose from the stern impeller pump at the thermostat housing and it did have water being pumped up there (what kind of pressure/water flow should I see?). Also very hot water in an almost steam spray comes out at the back of the boat, so water is circulating, but at what rate should this come out?(It doesn't seem like a lot. Should I Test again at higher rpm to see if temp climbs over 160?

 

[ziggy]

Re: overheating on Merc 140?

bobafett, i think that 155-160 is right on (maybe even perfect)for raw water cooled. a 140 t-stat starts to open at 140* and is full open at about 160*. so it seems to me your right where you want to be. my boat is a bit older than yours but has the same hot water, almost steam comeing from the back too. i also have hot water comeing out of the prop and a little hole at the front of the lower. one other thing i learned here on "the fourm" here is, that when ya turn on your garden hose the water is really spraying out around the drive. when ya start the engine there is a lot less squriting out around the muffs, as it is being pulled into the cooling system from the impeller. i'm guessing your ok. this is only my opinion though.....

 

[Laddies]

Re: overheating on Merc 140?

You cannot judge water pressure on a hose the water is being pumped into the unit, itneeds to be ran in the lake or a tank to tell for sure. Generally speaking if you hook to a hose and water comes out the exhaust without the engine running the impeller is going bad, no water means the imp is holding and should pump in the lake--Bob

 

[bobafett]

Re: overheating on Merc 140?

If the engine is off , the thermostat is closed, right? If so, then how can water ever come out exhaust when engine is off?<br /><br />Also,<br />At a constant 2000 RPM for a few minutes what kind of temp should be normal?

 

[MainstreetUSA1]

Re: overheating on Merc 140?

Water is always being supplied to the exhaust. At least if everything is working properly.<br /><br />If the t-stat is closed all the water being pushed by the raw water pump is being diverted to the exhaust manifold /riser at the t-stat housing. Once the t-stat begins to open, cool water pushed by the raw water pump mixes with water already circulating in the block and whatever is left over goes to the manifold and riser.<br /><br />If the engine is off and the t-stat is closed and your impeller is still good, the water from your garden hose and muffs shouldn't be able to make it past the impeller vanes and pump housing. If there are little to no vanes left, the water pressure from the muffs could possibly push the water up through impeller housing and out then through the exhaust.

 

[bobafett]

Re: overheating on Merc 140?

Thanks, Sound like good insight so I connected muff with the engine off and disconnected the hose the the t-stat housing. When the water was turned on, a slow steady trickle of water was coming out the end with the hose lying on top of manifold. If I grabbed the end and held up 8 inches or so water flow would stop. So does this mean some of the implellar vanes are gone and the whole impellar will soon fail? <br />When the engine is on I do have flow going to the t-stat housing but I don't know if it the right flow rate.

 

[Don S]

Re: overheating on Merc 140?

If that impeller is over 2 years old, it's past due to be replaced anyway. And with your clanking outdrive post, it's a perfect time to pull the drive and check everything and replace the impeller.

 

[MainstreetUSA1]

Re: overheating on Merc 140?

The only way to really know the condition of the impeller is to pull the lower unit, remove the pump housing and inspect the impeller. <br /><br />When I had an impeller go bad on my 3.0. I found bits of the vanes stuck at the t-stat housing and at the water inlet to the exhaust manifold.<br /><br />If you search the forum you'll probally find previous posts giving specs on how much volume the raw pump should produce in a given amount of time.

 

[bobafett]

Re: overheating on Merc 140?

Can pull the lower unit myself? Any special tools need or a hoist required?

 

[MainstreetUSA1]

Re: overheating on Merc 140?

Go Here: <br /><br /> http://www.mercstuff.com/waterpumpinst.htm <br /><br />This gives you a step by step proceudure on how to replace your impeller. Get a shop manual either from Mercury or a knock off Seloc or Clymer. I have the Clymer for my Volvo SX drive but I've ordered an official manual because the Clymer is a bit vague on some procedures.<br /><br />Don't forget you'll need to replace the raw water pump housing gaskets if you open it it up to change/inspect the impeller. If you search the forum you'll see advice on pulling the lower unit and getting it back on with the water tube, drive shaft and shift shaft all lined up. Very similar to merc outboards.