Low water pressure and Over Heat Warning

[e.wallace]

I have a 1991 Mercury 2.5L 200Hp. I just got the boat so don't know much about it. I first noticed when I run the engine at idle I don't get any water from the tell tale water tube. If I reve the engine I get a great stream. As the engine backs down it starts to spit then quits and you can feel air pulsing from the water tube. I was told the thermostat has to heat up but this happens even when it is hot. At higher rpms I start getting water but not any at idle even after long run. I ran it for a while yesterday at the lake and made about a 15 minute trip across the lake and just as I came to the dock and brought it to an idle the warning horn sounded. This is the first timne it has ever sounded. I reved the engine and the horn went away. As it idled for about 10-15 seconds it came on again. I didn't have water coming from the water tube. I reved the engione again the alarm went off and the water started to flow at higher rpm the stopped again at idle. Horn sounded again! I pulled the lower ubit and checked the water pump, is in great shape. Does the thermostat get stuck, will it cause this? Does the water get pushed out the water tube before or after the thermostat?<br /><br />Any help would be greatly appreciated!!!!!<br /><br />Thanks,<br /><br />Eric

 

[rickdb1boat]

Re: Low water pressure and Over Heat Warning

The water pump impeller can LOOK great, but still be bad. The vanes take a "Set" and at low speed or idle will not pump enough to cool the engine. Then when you get going it spins a whole lot faster and cools better. Replace the pump if you don't know when it was last serviced. Check the T-Stats while your at it..

 

[andrewkafp]

Re: Low water pressure and Over Heat Warning

When you have just run the motor hard and then bring it back to idle That is when the motor is at it's hottest. The impeller is supposed to flatten out the vanes and deliver more water at idle, because it's obviously spinning slower, as Rickdb1 said.. If you idle for a minute, does it cool down (You should be able to touch the stream) or does it stay hot. While you had it apart, you SHOULD have replaced the impeller.(Cheap and easy).<br />Do you have a pressure gauge ? What does it read ?

 

[e.wallace]

Re: Low water pressure and Over Heat Warning

I don't have a pressure gauge. I have noticed that when I touch the stream of water when at higher rpm the water is hot. When I looked at the impeller I noticed the impeller made a tight seal against the housing and the blades seemed still very soft and conformed to the housing. all blades where there and didn't show much wear.

 

[e.wallace]

Re: Low water pressure and Over Heat Warning

Also, at idle I DON'T get a stream of water.

 

[KCLOST]

Re: Low water pressure and Over Heat Warning

Those blades on the impeller really shouldn't be that soft. They should be about as rigid as tire rubber. I agree with RB. It sounds like your impeller is not doing it's job at lower rpms...<br /><br />Change it, as well as the stats first. I bet that will solve your problem. There should always be some water coming out of the pee hole even with the stats closed. Mine just spurts lightly until the stats open and then it becomes a fire hose. But at least there is some water circulating at all times. If no water is coming out of the tube at idle (especially when the engine is warm to hot), you most likely have a water pump problem, no if, ands, or buts about it...

 

[shelbydriver]

Re: Low water pressure and Over Heat Warning

after many overheat conditions after replacing my upper pump cover and impeller 2 times. I found my impeller keyway slipped the 3rd time and also the lower pump housing was warped on the top where it seals against the top part. I got the bottom part new and the problem went away. Inspect closely.

 

[e.wallace]

Re: Low water pressure and Over Heat Warning

The p-hole gives water at mid range rpm but none at idle when hot.The stream is intermittent when at mid range RPM too. Could the therms be bad and the water coming out only because the water pressure is high enough that it overcomes the pressure relief? When I pulled the lower unit I noticed there was no seal on the pick up tube, should there be? Also no seal or slinger on the drive shaft going into the water pump. My Clymer manual sucks and doesn't really show very well the seals that are there or how to install.

 

[KCLOST]

Re: Low water pressure and Over Heat Warning

There is no seal on the pickup tube, but there is a white guide tube to help align the pickup to the exit tube of the pump housing. I believe there is a rubber washer type thingy that goes over the drive shaft that works as a seal for the pump cover??

 

[e.wallace]

Re: Low water pressure and Over Heat Warning

Th pick up tube is in place and the impeller seems to be fine(no missing fins and still expands to conform to pump housing. I am still concerned about the stream of water coming fomr the p-tube not being steady at higher rpm's. Low flow-high flow-then low flow again at higher rpms.

 

[KCLOST]

Re: Low water pressure and Over Heat Warning

If you are 100% sure about the impeller and have no concerns about whether or not it is pumping correctly, let's move to the next possible culprit.<br /><br />But let me first say, I'd change the impeller, pump housing, gaskets by buying a water pump kit. Not a lot of money...<br />Then I'd replace the stats. Not a lot of money..<br /><br />Then I'd replace the poppet. Again with a kit that includes gaskets, grommets, valve, spring, the whole shabang. Not a lot of money.<br />There is a possibility, (based on you description of what is happening) That the poppet valve is stuck open. This will allow water to exit the jacket area without it fully circulating around the engine. This could explain why you have no water exiting the pee hole at idle, and intermittantly at higher rpms. This will also cause higher temps at lower rpms due to the fact that the water exits the system through the poppet and doesn't get enough around the block to cool it down.<br /><br />Do you see water exiting the upper exhaust during idle. If so, that is a symptom that your poppet is not closing when it should. The poppet is at the bottom of the block, so if it is open all the time, it won't allow water to get up higher where the heat is really generated. It should only open obviously at higher rpms, when water flow is more than enough than can be handled by the pee hole.

 

[robalofish]

Re: Low water pressure and Over Heat Warning

If you want to save yourself a lot of headaches <br /><br />Change the water pump complete, new base, new impeller, and new upper housing.<br /><br />Change both thermostats. You can check them when you remove them just to see if the are functioning, but I would replace if I had them out.<br /><br />Change the poppet valve diaphragm and gaskets.<br /><br />This will also give you a reference point for maintenance.<br /><br />PS I agree with RB this sounds like an older water pump impeller that needs replacing.<br /><br />Good Luck<br /><br />RFish >()> <br /><br />PSS I was typing this as KCLOST was replying I just don't type as fast. I fully agree for the price of the parts if you have it open replace them and theres no doubt there good.

 

[e.wallace]

Re: Low water pressure and Over Heat Warning

Thanks for all the replies guys. I am going to go to the dealer and start with a new impeller kit. Pump housing base and all. (Told it could be warped) Will change the stats just in case. If that doesn't do it I will change the valve. will keep all informed.<br /><br />Again, thanks for all the replies, it is greatly appreciated!<br /><br />Eric

 

[e.wallace]

Re: Low water pressure and Over Heat Warning

UPDATE!!! I changed the water pump along with new housing, base, gaskets, slinger and all. Ran water through engine and notice the same situation happens. Ran up to 2000 Rpm and got a pulsating stream of water(therms opening and closing) from tell-tale water tube. I then Let it idle and only noticed a light pulsating air coming from tube and only a mist or spit of water every couple of seconds. I am thinking I am not getting the engine hot enough for a stead stream with cold tap water(using muffs) and really need to get ot and run it then see what it does? I can put my hand in the stream of water when I ran it at 2000+ rpms for a few minutes and the water was very warm but not hot. I have only gotten the alarm one time after running it all day off and on. And as I reved the engine it stopped then came back after a few seconds. This was all before I changed everything in the water pump section. What does anyone think?<br /><br />Just want to make sure I have fixed it, don't want to rebuild the motor due to overheat!<br /><br /> Thanks again for all the replies!

 

[KCLOST]

Re: Low water pressure and Over Heat Warning

Was there any water coming out of the upper exhuast while you were running the engine.. Not the prop but the upper exhaust ports...

 

[dashaway]

Re: Low water pressure and Over Heat Warning

What is the poppet you are referring to? <br /><br />Thanks

 

[e.wallace]

Re: Low water pressure and Over Heat Warning

I didn't notice any. I did look a few times.

 

[e.wallace]

Re: Low water pressure and Over Heat Warning

I think I was talking about the overpressure poppet but was told the poppet would only be a problem at high rpms not at low rpms so I don't think it is malfunctioning.

 

[BlackKnight755]

Re: Low water pressure and Over Heat Warning

KCLOST, <br />Is the poppet valve replacable from the outside of the engine, or do you have to seperate the engine block from the housing? I am having similar problems with mine except I have not heard the buzzer. I am going to replace the pump, pump housing, the stats, and if I can change the poppet valve without tearing the motor apart I will change it too.<br />Thanks for the info,<br />Wayne

 

[e.wallace]

Re: Low water pressure and Over Heat Warning

Wayne, <br /><br />I beleive the relief valve is on the side of the block right head I believe? My Clymer manual sucks and doesn't show or depict the relief valve very well.