1989 OMC Overheating only when in the water

[tjlowery]

Hey all, I am hoping that you guys can help me out. I recently purchased a 1989 H180 and have been having an issue with the boat overheating. I replaced the impeller, and it worked fine on muffs. I did the check to make sure that it was getting 4-6" of water when the engine was started. It did and everything seemed fine. The engine water pump is pumping and when running on the muffs everything is fine. However when I put it into the lake and try to run it, within a few min the temp rises and it begins to overheat.
Today while sitting in the lake I pulled the raw water inlet and realized that it was not pumping water, i pulled the upper drive cover to inspect it and realized that there were bubbles coming from where the impeller pump vent line connects to the lower unit. I tried running it with the vent line disconnected with the same results. Nothing!! It still overheats.
Any ideas what could be causing this? I have back-flushed the system from the t-stat to the impeller, no pieces where present, and there were no clogs.
Could the culprit be a faulty impeller? Possibly the seal between the upper and lower units? If so, how do I check which is causing this?
Please help, I have been back and forth to the lake everyday, and I don't seem to be any closer to fixing it.

Thanks,

 

[Brian_S]

Re: 1989 OMC Overheating only when in the water

i just had the exact same issues as you, no overheat on the muffs, but in the water..... overheat.

mine was indeed the impeller, i had it replaced 2 weeks ago, and now ive moved on to other problems ..... heh .... damn it!

have it checkered out.

 

[sea wolf]

Re: 1989 OMC Overheating only when in the water

Yep, sound like a bad impeller. One of the worst things u can do to your engine is to keep running it while it's overheating, so I would park it until it's fixed. What size engine?

 

[tjlowery]

Re: 1989 OMC Overheating only when in the water

It's the 4.3L. I recently replaced the impeller, and I am still having issues, however I am concerned with the condition of the impeller. I pulled the cover off when the water was not pumping the way it should, and it look as though some of the fins were worn.

When the impeller was initially installed it was not fully seated, so when the cap was put on it compressed the impeller a bit, folding the fins ever so slightly. Would this cause the pump to not pump water? I do have to say that the pump was pumping a little bit, not even enough to raise the water level in the line more than an inch or so.

Also, is it normal for air bubbles to come from where the vent line exits the upper housing and into the lower? Just want to make sure that I get everything replaced that needs to be.

 

[tjlowery]

Re: 1989 OMC Overheating only when in the water

Well just got back from the Marina...45 min one way, 5 min to get the impeller and another 45min back. Hopefully this will solve the problems. do all of the fins on the impeller have to bend in the same direction? i would think that they do, but I have seen some pics where they do not.

 

[tjlowery]

Re: 1989 OMC Overheating only when in the water

Got the impeller installed and took the boat out today, the impeller was pumping water but only when the RPMs were up around 1000 or more. Is this normal? If I was trolling around the heat would build rather quickly, but once I sped up it would drop again.

Also, I had removed the thermostat because it was stuck shut and was not opening at all. If I leave this out what will happen? Will this cause my engine to run hotter at all times, or cooler? Trying to determine if this was causing the problem above.

 

[Chuckyd973]

Re: 1989 OMC Overheating only when in the water

I would check the entire cooling system from the impeller to the exhaust. Make sure the water flows.....all you need is a few minutes of over heating to burn up yur motor, warp heads and manifolds etc etc. Out of the water would pull the water inlet hose of the back of the stern drive and put a garden hose into it and clamp it down, turn it on and open up all of your bleed points. I have found that if there is a blockage in the system the impeller will pump water in but it will heat up and burn out an impeller if it can not exit teh cooling system.

Chuck