Mercruiser Cooling Problem

[Have Fun Today]

I have a 1997 Mercruiser 5.7LX with an Alpha One stern drive. I replaced the impeller today, the old one looked fine but I heard it was good to replace annually. After completing the installation and doing a test run on the trailer, the stern drive didn't suck any water from my garden hose connection like it used to. I didn't want to let it run too long. I removed the lower gear housing and checked the assembly. Everything looked normal, and new impeller blades were oriented in the proper direction. I checked to ensure the impeller spun with the drive shaft. After reassembly, still no water sucked from the garden hose connection. Drive shaft is connected to upper gear housing, and I verified the water tube connected as well. Can anyone help?

 

[180shabah]

Re: Mercruiser Cooling Problem

How did the water pump housing look? they can wear also.

 

[Have Fun Today]

Re: Mercruiser Cooling Problem

The water pump housing looked fine outside, smooth and shiny on the inside. Old impeller showed no signs of wear except for the blades being bent from turning as expected. I followed the instructions in my Seloc repair manual. It didn't say to coat the inside of the water pump housing with grease so I didn't. Also, I replaced all gaskets and o-rings on the water tube.

The boat used to run in salt water and I cleaned out a lot of salt deposits but nothing appeared to be blocking the water flow.

 

[180shabah]

Re: Mercruiser Cooling Problem

I guess the first thing to do is, disconnect the water hose at the power steering cooler and fire te engine up. See if you have water at that point. You will only need to run. it for a few seconds. This will split your cooling system. If you have water flow then the problem is in the engine or exhaust, if you do not have water flow here, then the problem is in the drive.

 

[Have Fun Today]

Re: Mercruiser Cooling Problem

"disconnect the water hose at the power steering cooler and fire te engine up..."

I've seen this advice given on several different threads related to the same problem. Won't this damage the engine to run, even briefly, without cooling water (not that I haven't done this already by accident)? How long does it take to overheat and cause engine damage?

 

[Bondo]

Re: Mercruiser Cooling Problem

As long as the motor is Already full of Water,.....
The Few Seconds you need the hose Off,..... Won't hurt a Thing......
For That Matter,.....
If the motor was Dry,.... It won't hurt for a Few Seconds,.......30/50 secounds should be long enough to See Water Flow.......

 

[Don S]

Re: Mercruiser Cooling Problem

Without water going thru the exhaust, you could burn up those rubber exhaust hoses between the risers and the Y pipe, so keep your runs under 30 seconds. But it shouldn't take more than a few seconds to know if the pump is working or not.
When you changed the impeller, did you make sure the gaskets were on the right way? They will only fit one way easlily, but have seen them in wrong and the pump will suck air, not water.

 

[Have Fun Today]

Re: Mercruiser Cooling Problem

I disconnected the hose and did a short engine run, no water entering from the drive unit. I removed the lower drive unit and inspected the pump, all is well. When I removed the lower drive unit, the water tube was connected properly. Gaskets are installed correctly (as per the Seloc repair manual diagram) so all holes line up. The impeller was connected to the drive shaft via the key, so it had to be turning. I ran water backwards from the engine copmpartment through the hose to the water tube in the drive unit, it flowed freely and didn't appear to be any restrictions. Under the pump housing there is nothing that restricts the water flow into the drive unit and pump.

I'm not sure at this point, don't want to reassemble it again until I know the problem.

 

[Coors]

Re: Mercruiser Cooling Problem

(as per the Seloc repair manual diagram
I imagine that Bondo has Kevin's email..
I go hide now.

 

[Don S]

Re: Mercruiser Cooling Problem

You never will figure it out using a seloc manual.
Here's a link to the OEM manual
http://www.boatfix.com/merc/Servmanl/14/14cover.pdf
Go to section 3B and it will explain how to inspect the pump and impeller.
Did you install new gaskets? If not, it will suck air, not water.

 

[Bondo]

Re: Mercruiser Cooling Problem

(as per the Seloc repair manual diagram)
I imagine that Bondo has Kevin's email..

Naw,..........

I just post at the ABC forums,+ He finds Me...........................

 

[Have Fun Today]

Re: Mercruiser Cooling Problem

Those OEM manuals are very useful, thanks for the link to them!! I never used any gasket sealer but the OEM manual says to use it, maybe this is my mistake. I'll try again with a fresh gasket, the one that came with the impeller kit is now covered with gear lube. Another hour tomorrow and couple more quarts of gearlube and hopefully working again.

 

[Have Fun Today]

Re: Mercruiser Cooling Problem

I reinstalled the impeller again, this time with gasket sealer. It's a little better, getting some water flow into the engine compartment after running for about 30-60 sec, not as quick as I expected. I have a copule of questions now:

1. How hot should a Merc 5.7L idle with garden hose and muffs? I shut it down as it approaches 180. Don't want to stick it in the lake and run faster until I know I can get back.

2. Is it normal to see steam in the exhaust? I've never seen this before, and there is not as much water dripping as expected.

3. Finally, should I notice a decrease in the amount of water spilling out from the muffs as the impeller begins to spin?

 

[180shabah]

Re: Mercruiser Cooling Problem

180deg is too hot.

It's hot because you still don't have enough water flow.

You now have steam in the exhaust because it is too hot because you still don have enough water flow.

You don't have as much water dripping(it should be pouring) out the back because you still don't have enough water flow.

Your raw water pump is rated for 16-18 GPM, there will be no doubt when it is pumping at normal capacity.

 

[xltier]

Re: Mercruiser Cooling Problem

did you replace the thick rubber grommet in the impeller housing where the shaft goes thru the top of the cover.its a bugger to get it in but its very important for water flow.[ask me how i know]

 

[Have Fun Today]

Re: Mercruiser Cooling Problem

I did replace it...wasn't difficult at all though. It just slid over the shafe using the tool provided with the impeller kit.

xltier, please tell me, how do you know it's important for water flow. The rubber grommet was missing when I disassembled the lower gear housing. As far as I know, my engine was running fine before I changed the impeller.

 

[xltier]

Re: Mercruiser Cooling Problem

im not talking about the one that sits on top.this one goes into a groove in the pump cover and makes a seal around the shaft.then there is the one that just slides down the shaft after you assemble the cover.when i left mine out cause i didnt know there was one because my old one had melted,it would pump under pressure from the muffs but wouldnt draw the water in on its own in the lake.

 

[Have Fun Today]

Re: Follow-Up...Mercruiser Cooling Problem

Re: Follow-Up...Mercruiser Cooling Problem

Got a call from the boat shop today,they said the impeller and water flow was all fine. Problem was the thermostat, just needed to be replaced to get the water flowing into the engine.

 

[tsturgis]

Re: Mercruiser Cooling Problem

I have a problem/question as well... I have a 2002 496 mag merc. The antifreeze is leaking out of the heat exchanger opposite the thermostat side. I have replaced the rubber seal and hose clamps twice, and it continues to leak. I have been told that this is a common problem with these engines, has anyone ever heard this before? I can not figure out why it is leaking. Any advice would be greatly appreciated!

 

[180shabah]

Re: Mercruiser Cooling Problem

tsturgis - you need to start a new thread instead of adding to one that is over a year old.