3.0 Mercruiser overheating

[pfd]

Hi... <br /><br />I have a 1987 3.0 mercruiser that just started to overheat. Temp used to be around 170. Now 200+. I read some post and thought that my impeller was gone. Plus rubber pieces in the intake on the outdrive good indicator. I dropped the lower unit. It's a alpha one. I replaced the impeller and it needed it. The old one was done. Put everything back together. Starts great, temp right back up to 200+. This is fresh water cooled. Before the impeller install, I check the t-stat hoses and water pump on the engine and all seemed fine. I forgot to say this is on the muffs on garden hose.<br />All the hoses seem fine. The problem is that I'm not getting water to the exhaust manifold or to the water pump on the engine. So I turn the hose on with engine off and pull the intake hose off to the T-stat. Hardly any water, only a trickle. Even with the engine running same deal. <br />I have the same problem now the new impeller is in. I thought it was the impeller! I also replaced the t-stat while i was there.Now what<br />??????<br />I'd rather diagnose rather than be a parts replacer.<br />Risers? <br />Bellows? <br />no clue.

 

[tommays]

Re: 3.0 Mercruiser overheating

did you install a compleat pump ?<br /><br />if you have no water flow it sounds like you may not have gotten the water tube between the upper and lower connected correctly<br /><br />tommays

 

[pfd]

Re: 3.0 Mercruiser overheating

I just replaced the impeller not the entire pump. <br />It went together fairly easy. So I must have missed alined it.<br />Well that seems to be the case then. I just went out to check to see if the hose from the outdrive through the transome was plugged. No such luck.<br />So the tube from the pump to the upper part of the out drive is out of line eh?<br />Well that's what I'll do next.<br />Dropping the lower again.<br />Thanks for the reply.

 

[tommays]

Re: 3.0 Mercruiser overheating

its hard to say but some old pump vanes may be bocking water flow also<br /><br />it may be nessary to backflush the hose connnected to the t-stat back through the drive with the lower off to be sure you have water flow going through <br /><br />you want to find as much of the old pump as you can<br /><br />did the impeller kit have new gaskets ? <br /><br /><br />tommays

 

[Don S]

Re: 3.0 Mercruiser overheating

You might want to look at the hose from the drive to the transom shield. When they get old and brittle, they kink and will cut off the water supply.<br />If you happen to keep the boat in salt water, near fresh water outlet. I have also found shells that grow in the drive and eventually plug up the tube that goes through the transom sheild at the sharp bend. I guess anything could get stuck there, but it's worth a check if your raw water pump is in good shape.

 

[pfd]

Re: 3.0 Mercruiser overheating

The raw water pump is in good shape. No new gaskets but the old ones seemed fine. Though when When I replaced the impeller I noticed a plastic tube around the copper tube coming off the pump. It was in terrible shape and didn't look as it served any purpose. It was brittle and broken. Is this important? Does it serve a purpose more than protecting the copper tube? Like I said it was in rough shape so I'm not sure if it was supposed to be longer and connect to the upper part of the outdrive. The copper tube looks as though it would be long enough on its own. I have flushed the hose from the t-stat intake to the outdrive and it seems to be clear. I can blow water through it, but very little water if any comes out the intakes on the lower unit. The water comes out the exhaust port through the prop. If the alinedment isn't the problem, what's the easiest method to replacing the hose from the upper through the transome.I doesn't seemed plug but it doesn't look that great. Do I have to remove the entire outdrive or will it pull through to the inside?

 

[tommays]

Re: 3.0 Mercruiser overheating

http://www.mercstuff.com/howdoi.htm <br /><br />this should give you and idea whats involved in changeing the hose and other parts.<br /><br />tommays

 

[pfd]

Re: 3.0 Mercruiser overheating

Well thanks for the advice but to no avail, still no water. The water tube through the transome has to be plugged. I've realined the tube and it was in. So I must have missed something. <br /><br />Still plugging away. <br /><br />Again, thanks for the advice.<br /><br />PFD

 

[milkyway]

Re: 3.0 Mercruiser overheating

You said "I have flushed the hose from the t-stat intake to the outdrive and it seems to be clear. I can blow water through it, but very little water if any comes out the intakes on the lower unit. The water comes out the exhaust port through the prop."<br /><br />With the outdrive removed, if you put the garden in the hose thatleads to the thermostat from the transom, are you getting the same amount of water coming out? This is what Tommays said. This is to verify that the hose is clear of any obstruction.<br /><br />If it's clear, then go back and reassess the installation of the water tube that's goes up from the impeller. You said it was installed correctly. How were the orings on this tube? Mine has 2 o-rings.<br /><br />Did you correctly install the new impeller? Is it locked on the shaft? If not locked or keyed, the impeller will not spin with the shaft and therefore not pick up water. <br /><br />When you have verified all these, the only thing left could be a plugged tube, as Dons says. Put the garden hose to the upper tube and see if water comes out.

 

[pfd]

Re: 3.0 Mercruiser overheating

Well I fixed it! I removed the lower again and flushed the hose from the t-stat to the outdrive with the lower off this time. No Plug!<br /><br />So then I went after the pump. The impeller was in correctly, correct direction all gaskets good. Seated tighly.<br /><br />Finally I looked at the tube from the pump to the outdrive. That was seated correctly. There was a small rubber seal that's supposed to wrap around the water tube and seal into the hole of the outdrive. Of course it's jammed into the hole and blocking most of the water. Also water was flowing around this tube, not up into the outdrive.I replaced rubber seal and reassembled the lower, VIOLA!<br />She runs great again! Water temp back down to aprox. 140 and flowing water beautifully. The water is also only coming out of the rear exhaust point below the transome, not through the prop.<br /><br />Thank you all for all of the advice. It was a big help!!!<br /><br />I can't say enough.<br /><br />PFD

 

[milkyway]

Re: 3.0 Mercruiser overheating

Happiness is what this forum tries to bring to boaters and fixers. My weakness is the engine itself, so I hope I can learn more about it. And the most expensive part.

 

[erikjohnnelson]

Re: 3.0 Mercruiser overheating

PFD,<br /><br />If you are still checking this post, please give me a call. I have an 89 3.0 that is overheating. I'd really like to talk to you before I dive into this one. Give me a call at 612-382-4723 or shoot me your number at erikjohnnelson@hotmail.com