89 Mercruiser 3.0L Alpha 1 Gen 1, overheat at idle, fine at higher rpm

[toneybrown]

Ok, this new boat is getting very aggravating. After address multiple issues in another post, I finally got the boat out on the water today to see if my fixes worked. Everything thing seemed fine, temp was a little over 145 at first. After leaving the dock and cruising about 15mph the temp seemed to stay steady, just over the 145 mark. I throttled down to idle in neutral and notice the temp gauge starting to creep up. It got to the mark between 145 and 220 F. Not sure exactly what that temp is..... Worrying of overheating I started back to the dock and the temp drops back down to just over 145F.. I opened her up to about 30mph and the temp stayed just over 145F the entire time. Tie off at the dock after cruising in, temp climbs back to the notch between 145 and 220. Kill the engine, open up the cover and the engine doesn't seem hot, exhaust is warm to touch but not scorching.

After putting the trailer in the water and going back to the boat to drive it up. I start the engine and it is nowcloser to the 220F mark. This was after being turned off for several minutes, the temp was reading higher then when it was actually running.

So, It has a new impeller and new T-Stat. Had the manifold off and it wasn't very corroded at all, seemed pretty clean. Didn't check the exhaust elbow. I have pulled the hose going into the T-stat housing and it had lowish flow on muffs at idle, and decent flow at higher rpm (Not sure exactly as Tach not working...).

Does this sound like a blockage someplace? Maybe oil cooling canister thing? What is the process of back flushing this drive?

Thanks again for any help!

 

[Bondo]

What is the process of back flushing this drive?

Ayuh,...... Drop the lower unit, 'n recheck the impeller installation,.....

While the lower unit is off the drive, stick yer garden hose into the hose at the t-stat that comes from the drive, 'n give it all the water ya got,......

At idle, with a good supply of water, when ya do that Test ya did with the hose off the t-stat, water should run up 'bout 4 or 5" straight up, before it topples down over itself,....

 

[toneybrown]

Thanks, was not sure if I needed to drain and remove the lower unit. Now to find the motivation to tear into it today.....

 

[toneybrown]

Ok, drained and removed lower unit. Removed the impeller housing and the impeller looked brand new, nothing out of the ordinary that I could tell.

Connected water hose to hose that connects to T-stat housing. Turned the water to it and a nice steady stream of water flowed out of the outdrive from the little metal spout the impeller housing attaches too. Let it run for a while to make sure it was cleared out.

Reattached the lower unit, refilled with gear oil, attached muffs and fired her up. Hose from the impeller was not moving any water, or very little at all at idle.......when giving it some throttle a decent stream of water started to flow. Back to idle and it reduced to a mere trickle. I'm lost.

I only replaced the impeller itself, not the top or bottom housing. Could something there be causing the issue? I have a water flow issue and don't know where to look now.

 

[Bondo]

I only replaced the impeller itself, not the top or bottom housing. Could something there be causing the issue?

Ayuh,...... Anything less than Perfect surfaces in the housin's is unacceptable,.....

 

[toneybrown]

Ayuh,...... Anything less than Perfect surfaces in the housin's is unacceptable,.....

Looks like I will be ordering a new impeller kit with housing. Could there be anything else that you could think of that could cause this low flow at low rpm issue?

Thanks for the help!

 

[Scott Danforth]

Looks like I will be ordering a new impeller kit with housing. Could there be anything else that you could think of that could cause this low flow at low rpm issue?

Thanks for the help!

when you replaced the impeller, was the old-one missing any parts. if so, you need to find them.

 

[toneybrown]

when you replaced the impeller, was the old-one missing any parts. if so, you need to find them.

Not really, it was pretty much intact, no big pieces missing. The housing did seem to have some slight melting around the top opening and around the metal sleeve that fits inside of the upper housing.

 

[QBhoy]

Check the thermostat is working.
Just one point with noting....engines in planing hulls work best when on plane or at just over tick over. If you are in between and loading the engine up by being just less than planing (ie the bow up in the air and the flat of the hull pushing water) it will obviously be working the engine harder...and not achieving much forward headway.

 

[zellerj]

When this happened to me, it turned out to be a pinched water hose because it was cut too long. The pinch would slow water when it was not forceful at low RPMs, but would open up with more pressure. Check to make sure the rubber hose from the outdrive through the transom is not kinked.

 

[toneybrown]

Check the thermostat is working.
Just one point with noting....engines in planing hulls work best when on plane or at just over tick over. If you are in between and loading the engine up by being just less than planing (ie the bow up in the air and the flat of the hull pushing water) it will obviously be working the engine harder...and not achieving much forward headway.

T- Stat is brand new, was never in a hull up position while in the water, running at speed was better then at idle. Idle is the issue as I am getting very little water when at idle rpm.

 

[toneybrown]

When this happened to me, it turned out to be a pinched water hose because it was cut too long. The pinch would slow water when it was not forceful at low RPMs, but would open up with more pressure. Check to make sure the rubber hose from the outdrive through the transom is not kinked.

Are you talking about the hose that runs across the top of the engine or the one that runs from the transom to the oil cooller?

 

[QBhoy]

Ok...clearly an impeller or pick up/delivery issue.
Or still worth looking again at the T Stat.

 

[Scott Danforth]

Not really, it was pretty much intact, no big pieces missing. The housing did seem to have some slight melting around the top opening and around the metal sleeve that fits inside of the upper housing.

the melted housing is a smoking gun.

by the way, to check if you have good water flow, at 1100 RPM you can fill a 5 gallon bucket in about 20 seconds

 

[toneybrown]

Ordered a new impeller kit that includes the housing. Going to replace everything when it arrives and pray that the water flow at idle is a geyser!!!!!

 

[zellerj]

Are you talking about the hose that runs across the top of the engine or the one that runs from the transom to the oil cooller?

I'm talking about the water inlet hose in the bell housing near the three bellows. Sometimes when it is replaced it is not cut to the correct length and kinks. Usually when one turns to starboard the kink straighten outs. My engine got hotter when I held the helm to port, and cooled down when I turned to starboard.

 

[toneybrown]

I'm talking about the water inlet hose in the bell housing near the three bellows. Sometimes when it is replaced it is not cut to the correct length and kinks. Usually when one turns to starboard the kink straighten outs. My engine got hotter when I held the helm to port, and cooled down when I turned to starboard.

Ok, I'll look back there and see if the hose is kinked or crimped at all.

 

[toneybrown]

Ok, drained and removed lower unit. Removed the impeller housing and the impeller looked brand new, nothing out of the ordinary that I could tell.

Connected water hose to hose that connects to T-stat housing. Turned the water to it and a nice steady stream of water flowed out of the outdrive from the little metal spout the impeller housing attaches too. Let it run for a while to make sure it was cleared out.

Reattached the lower unit, refilled with gear oil, attached muffs and fired her up. Hose from the impeller was not moving any water, or very little at all at idle.......when giving it some throttle a decent stream of water started to flow. Back to idle and it reduced to a mere trickle. I'm lost.

I only replaced the impeller itself, not the top or bottom housing. Could something there be causing the issue? I have a water flow issue and don't know where to look now.

One thing I want to add to the back flushing. I just thought of this after looking at the hoses and things. When I turned water on, most of the water was coming out of the lower unit out of the metal pipe that connects to the impeller housing.

HOWEVER, I did see some water coming from the transom area. It wasn't a lot of water, but should all of the water be flowing out of the lower unit?

 

[Bondo]

HOWEVER, I did see some water coming from the transom area. It wasn't a lot of water, but should all of the water be flowing out of the lower unit?

Ayuh,.... Back-flushin', all the water should come outa the copper tube,.....

 

[toneybrown]

Ayuh,.... Back-flushin', all the water should come outa the copper tube,.....

Hmm, so where could the water be coming from?

The majority was coming out of the tube, but not all. Is there a hose or connection someplace in the upper gearcase that could be leaking? Could it be the hose from the lower unit that goes to the transom?

Looks like I'm going to pull the lower unit again tomorrow, attach the hose and check to see if I can find the source of the leak. I assume if it leaks during backflushing it could be letting water leak out before it makes it to the T-stat housing.

It wasn't very much water, so it definitely isn't the cause of the low flow issue, but can't be helping either.

I'd like to figure it out before replacing the Impeller housing and refilling with gear oil.

I swear, I have spent more money on this boat in the month I've had it, then the 10 years I had my last boat with an OMC Cobra drive.