Mercury issues?

[ChuckN]

I need help from a Mercury motorhead. I've never owned one of these black motors

I recently bought a boat with a '94 Merc 175XRi on it. I changed the water impeller, seals, etc myself and followed a correct procedure according to detailed instructions in a manual. When I bought it the impeller was shot.

When this engine idles for approximately 5 minutes the water stream out of the engine is quite hot, and the head on the engine is hot. The "pee" stream seems to spit and after idling awhile it would flow out in a light stream. At more throttle the stream is good and everything is perfect as far as engine temp (warm) and water cooling the engine. No alarms have gone off.

Is this normal for this motor? The mechanics I have talked to can't tell me for sure. I have nothing to compare to.
I have torn the lower unit off several times to make sure everything was installed correctly and it was (according to the manual and mechanics who I talk to).

Every outboard I have owned had a nice stream that flowed with force and hardly ever changed temperature like this motor.

Thanks

[IFallsRon]

Are you running the motor with muffs or in the water? You can get a false overheat warning sometimes with the muffs. Even though you have a steady stream of water with the muffs, a repair guy told me that the back pressure from having the lower unit submerged can make a difference.

[ChuckN]

I'm running the boat in the lake. Water temp 44 degrees.

Yes, I agree the muffs do give false readings on some motors.

[Surface Tension]

I believe the tell tail is after the thermostat on that engine so the water will be hot and won't come out till after the engine warms up. If the alarm and sensors are intact you should be fine. For piece of mind you could test the thermostat and poppet valve, while your at it look for any debris that could be causing obstruction.

[ChuckN]

Thanks Ole, that's good to hear. The problem is the steady stream on mine is intermitent. Sounds like a "Mercury" thing.

[Ole1855]

I don't know about intermittant, because once mine started coming out it was steady, the uncle told me most of the cooling discharge comes out through the prop exhaust, the water spout is really only a visable indicator.

If I'm incorrect, I hope someone else chimes in, because I'm no expert on Merc's and I'd like to be sure what I'm saying is correct!!

Ole

[ChuckN]

I couldn't locate a thermostat and I was told by someone that this motor doesn't have a stat. I'll research further.

[Ole1855]

ChuckN,
I just picked my new boat up on Sat., it has a Merc. 175 EFI, before I'd take it I told the guy I wanted to make sure it runs, so we put the muffs on and started it. No water came out the indicator hole after about 1 minute of running so we shut it off so we didn't overheat the motor. The guy called his uncle that runs Merc's and he came over, he said how long did you let it run? We told him and he said the motor didn't get a chance to warm up and get the thermostat open. We put the muffs back on and let it run, the whole time watching the overheat indicator light, it took about 2 minutes and then a steady stream came running out.

Ole

[Killin Time]

Someone said the stream is just an indicator and I agree. I have also seen where the spiders like to use this as a home over the winter and will plug it up. I have only worked on my 40 and 115 inline six but the hose usally runs to the top of the engine. It wouldn't hurt to disconect it and let it run to see if you get the same stream and blow it out and see if you are carrying any passengers.

[Knotwood]

Sounds typical of some Mercs I've seen...several older Mercs used to shoot out very hot water, yet ran fine and did not over heat. Does the head or anywhere else get so hot you cannot hold your hand on it? We used to have this "crayon" called thermo-melt, it came in different temperature capacities. The idea behind this was you could draw a line on any affected area and it would melt at a specific temperature, letting the operator know if it exceeded the normal range. There are infra-red temp guns out now that instantly give you a reading, a lot more accurate.

[zepman]

I have a buddy that has had this same problem with his three year old 50 merc. Been in the shop three times and still can't get it right. Makes him very nervous being out on the water at all. More worried about his motor overheating than he is about having a good time and catching some fish. Needless to say--a Johnson or Suzuki will be on the back of his boat by the end of the month.

[ChuckN]

I looked into the motor some more and found 2 thermostats. It appears thats what was going on, but at least at high speed/RPM's the engine is running relatively cool. I guess it won't hurt to replace the stats as they did look old and discolored, and you never know if they will fail.

Thanks for everyone's help.

[Knotwood]

Did you find out why the impeller went bad? Was it just formed or actually scuffed? A lot of guys would run their motors for a minute out of the water before they left, and wipe out impellers that way. I'd do a compression test on the cylinders to see they are within range, say 10-15 pounds difference at most. Any more could mean they got overheated at some point. It is so hard to tell by the way they run, unless a good dyno test indicates otherwise, I've seen bigger engines pull skiers and still have out of round cylinders where they put out a lot less power than they are supposed to. Same goes when a cylinder drops out, hard to get a "seat of the pants" feel.

[ChuckN]

The impeller went bad because it's was old, formed, cracked, etc.. It's hard to believe it pumped water in the first place. These impellers should be replaced every 2-3 years for maximum performance.

I should do a compression test, but do I really want to know the results?? I'll pass for now as she runs well now.