Overheating and shift problems in my 1985 170 Mercruiser

Hi
I have two problems with my 170 mercruiser.
1) yesterday I was 5 miles from my home port in Provincetown, MA traveling at about 3000 rpm when my engine suddenly began to overheat. as the temp quickly reached 200 I shut down and anchored up until the engine cooled down to to 160. I added some water to the cooling but didn't have enough on board to fill the tank on the top of the manifold. I was able to restart the engine but any attempt to increase power over 1200 rpm resulted in a quick climb to the temp. At the lower speed the normal temp of about 125 was maintained and I crept home with it. Once back in port I topped off the coolant tank with a 50 / 50 antifreeze mix and started out again, but as soon as the rpms went over 1500 the temp climbed very fast and I was forced to shut down. I again idled back and the temp quickly dropped down to normal and I was able to move around the harbor and get the boat back on the mooring.
So what is the problem? I had the upper unit rebuilt 3 seasons ago and had a rebuilt lower unit installed 2 years ago. I only put about 100 hours a season on the motor so I am surprised to be having this kind of problem. Do I have to pull the boat from the water to work on this? Am I looking at a big expensive fix? Or is it a simple blockage I can fix in the water?
2) Assuming I can fix the first problem, I have a shifting problem too. I few days ago I reset the shift cables as per information I got from this forum and the manual, I was having trouble shifting into forward. Now it shifts pretty good into forward and reverse, but it is very hard to get it back to neutral, especially from reverse which seems to come out of gear very hard and jumps back into forward before I can pop it back to neutral. With the engine shut down it shifts just fine. Is this something with the shift stall switch? is this switch adjustable?
Thanks for your help
Frustrated old boat owner - Pete

Re: Overheating and shift problems in my 1985 170 Mercruiser

With 200 hours on it I would expect that the impeller needs to be replaced. If any pieces of the impeller are missing, you need to check under the forward heat exchanger cap for blockage. It does seem like you are having problems with the shift interrupter switch.

Re: Overheating and shift problems in my 1985 170 Mercruiser

Do you think it would be worth it to check the heat exchanger first? Can I remove the heat exchanger in the water with out sinking my boat? Or should I just bit the bullet and pull the boat? (pulling the boat is not an easy task and will take a half day to do)

Re: Overheating and shift problems in my 1985 170 Mercruiser

Provincetown boater said:

Do you think it would be worth it to check the heat exchanger first? Can I remove the heat exchanger in the water with out sinking my boat? Or should I just bit the bullet and pull the boat? (pulling the boat is not an easy task and will take a half day to do)

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That would be OK, look for blockage under the front endcap. The seawater flows through the tubes, the exchanger is probably above the waterline. What you might be able to is check the seawater flow by pulling the seawater hose off the front of the exchanger and briefly starting the boat to see how strong the flow is. Don't run for more than a few seconds or you could damage the shutters in the exhaust. Should be a good strong flow. You could also check the thermostat to make sure it is opening correctly.

Re: Overheating and shift problems in my 1985 170 Mercruiser

Thanks for the help
I hope to get back on board Thursday afternoon to run the test and check under the end cap. I took out the thermostat a few years ago so no worries there
I will let you know what I find

Re: Overheating and shift problems in my 1985 170 Mercruiser

Wonder if you may have ran over some trash in the water and blocked the water inlet long enough to roast the impeller?

Sounds like the shift interruptor isn't working or wired.

Re: Overheating and shift problems in my 1985 170 Mercruiser

Provincetown boater said:

I took out the thermostat a few years ago so no worries there

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Bad idea. You shouldnt run this engine without a thermostat. It has a disk on the top of it that moves when the thermostat opens, which blocks off the bypass hole in the exhaust manifold right above the thermostat. With the thermostat closed, the hole is open and coolant recirculates back through the engine without being cooled. When the thermostat opens the disk blocks the hole the coolant is forced through the heat exchanger. Leaving the thermostat out allows the coolant to go wherever it wants (i.e., back to the engine and not through the heat exchanger) and usually results in overheating.

Also be warned, this engine does not tolerate hot running for long, and even mild overheats will ruin the head gasket in no time at all. You may already be there.

Re: Overheating and shift problems in my 1985 170 Mercruiser

OK
I finally got back to the boat today as the winds let up. I ran a test by pulling the seawater inlet hose from the front of the heat exchanger and ran the engine for a few seconds. First thing that happened is that a good force of water came out from the heat exchanger as most of the water in it seemed to be blown out. At the same time there was a strong flow of sea water coming from the hose.
My assumption was that I was getting a good water flow from the drive unit, but why was I getting blow back from the exhaust side of the heat exchanger?
So at this point I pulled the front plate of the heat exchanger off and I saw no obvious blockage. I then pulled the heat exchanger and brought it home to flush out with a fresh water hose. When I back flushed the heat exchanger with the front plate off I noticed water only coming out from one side, so I pulled the back plate off too. When I look through the holes with a light on the other side I don't see any blockages in the holes.
Where do I go next?
Thanks for the help
Pete

Re: Overheating and shift problems in my 1985 170 Mercruiser

Provincetown boater said:

My assumption was that I was getting a good water flow from the drive unit, but why was I getting blow back from the exhaust side of the heat exchanger?
So at this point I pulled the front plate of the heat exchanger off and I saw no obvious blockage. I then pulled the heat exchanger and brought it home to flush out with a fresh water hose. When I back flushed the heat exchanger with the front plate off I noticed water only coming out from one side, so I pulled the back plate off too. When I look through the holes with a light on the other side I don't see any blockages in the holes.

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You would only get flow from some of the tubes with one end cap off. The water flows in the from through several tubes to the back and through several more to the front, back and forth before exiting. Make sure you have good gaskets on the endcaps to make sure none of the tubes are bypassed. The only thing left is the exhaust outlet, you may have some blockage there. pull the hoses off the power steering cooler and exhaust elbow to make sure they are clear. After that I don't know.

Re: Overheating and shift problems in my 1985 170 Mercruiser

I don't have power steering on this motor. Could there be a blockage in the exhaust outlet that would cause back pressure?

Re: Overheating and shift problems in my 1985 170 Mercruiser

Provincetown boater said:

1) yesterday I was 5 miles from my home port in Provincetown, MA traveling at about 3000 rpm when my engine suddenly began to overheat.

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A blockage in the outlet could be the problem. You could pull the hose to check, except you said this happened suddenly. Anything small enough to pass through the exchanger tubes should not block the exhaust outlet. I wonder if you may have blown a head gasket, or had a problem with the engine waterpump. Couple of things to check: You could do a compression check and a cooling system pressure check (can get tools from Autozone for free). Also pull the plugs and see if any of them are white, indicating water intrusion. You can also take off the radiator cap when it is cold and look for bubbles in the coolant. Do you have the manual, troubleshooting guide page 6A-3 Here is a link to download the manual: http://www.4shared.com/document/zTbCbkDD/Service_Manual_08.html

Re: Overheating and shift problems in my 1985 170 Mercruiser

Thanks so much for your help so far.
I have reassembled the heat exchanger end caps and run water through it, which it does freely. I am still wondering about the "blow back" I witnessed from the heat exchanger inlet when I was testing the water flow. Is this normal or is it an indicator of something not right?
I will be going back out to the boat, (weather permitting) Tuesday to reinstall the exchanger. Anything else I should check before I try it again?
Thanks again
Pete

Re: Overheating and shift problems in my 1985 170 Mercruiser

Hay P-town read this thread it may apply to you too: http://forums.iboats.com/showthread.php?t=498480 Good luck.

Re: Overheating and shift problems in my 1985 170 Mercruiser

So here is today's news
I went out to the boat today to reinstall the heat exchanger but before I did I decided on a whim to check to see if my mechanic had really removed the thermostat all those years ago when he recommended it and I said "do it". I always assumed that he did because my engine always ran cool after that, (about 120 or so). So before I did anything I took the hose off and stuck my finger up the housing and, you guessed it there was a thermostat there. I was so intrigued that I immediately set off to remove it to check it out. Not so smart since of course removing the housing wrecked the gasket and at the point I couldn't do any more testing until I replaced the thermostat. I rowed in and drove 30 miles to the local Mercruiser dealer who I called in advance to make sure they had the thermostat, only to find out when I got there that the thermostat didn't come with a gasket, and they didn't have one in stock. Are you kidding me how can you sell a thermostat with out the gasket.
I was able to do one test. I was able to blow into the water out fitting on the exhaust elbow and was able to pretty freely blow bubbles out the the drive unit so I don't think there is a blockage there. My thinking is that perhaps the thermostat was stuck open for all this time but that it suddenly closed and stuck and that caused my problem. At this point that is what I hoping for. If this doesn't work than I will likely haul the boat out this weekend and work on it onshore.
Pete

Re: Overheating and shift problems in my 1985 170 Mercruiser

Hi Stony,
Ok today I finally got the thermostat gasket and the time to go out to the boat and put everything back together. This time when I ran the engine she over temped even running at idle.
I pulled the sea water line going to the heat exchanger again and it was dry, ran the engine for a few seconds and now NO water comes through. I guess this mean the impeller is toast. Do you have a manual that shows how to replace it? Is this something I can do on the beach or do I need to haul out?
Thanks
Pete

Re: Overheating and shift problems in my 1985 170 Mercruiser

Provincetown boater said:

I pulled the sea water line going to the heat exchanger again and it was dry, ran the engine for a few seconds and now NO water comes through. I guess this mean the impeller is toast. Do you have a manual that shows how to replace it? Is this something I can do on the beach or do I need to haul out?
Thanks
Pete

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Sounds like it. I don't have a link to the manual, but I am sure someone will provide one to you here. In the meantime here are a couple of videos to look at. Unfortunately they are for a gen II so it is a little different than a Alpha I like yours. You do have to pull the boat, but it is not necessary to remove the whole outdrive, even though it is easier to replace the impeller "on the bench".
http://www.youtube.com/watch?v=tiCgHTrMKTw
http://www.youtube.com/watch?v=jXq35NOX8kw&feature=related

Re: Overheating and shift problems in my 1985 170 Mercruiser

HI Stoney,
So here is the latest update,
Got my new impeller kit yesterday and today I pulled the lower drive unit and the pump unit. I found a small baby oyster shell lodged in one of the passage ways. The impeller also looked a bit worn, but not obviously broken. I replaced it with the new and reinstalled the lower unit, new gear oil. Started it up with the muffs and the water pumping out looks good. Ran it for almost an hour and the temp never budged over 125, even when I ramped the rpms up to about 1500 for a couple minutes. So I guess I am ready to relaunch tomorrow on the tide.
One question I did notice a strong water flow coming up from a hole in the front of the drive. Is this normal or am I missing something?
I also adjusted the idle down to about 500 rpm, interested in seeing if it shifts easier now.
Thanks for your help
Pete

Re: Overheating and shift problems in my 1985 170 Mercruiser

It doesn't take much LOL. I think that water is just coming out of the exhaust bypass, and is OK. Glad things are working out .

Re: Overheating and shift problems in my 1985 170 Mercruiser

Another update:
Over night I was still worried about the water I saw coming out of the hole at the upper drive unit during my test yesterday. I finally found a reference to a drive unit manual on another thread this morning and I found that I did not properly reinstall the water seal in the upper drive unit before I inserted the copper water tube. (this seal came out when I pulled the lower drive unit).
I am now convinced that unless I take the drive off again and properly install the seal that I will likely have trouble again when I get up to cruising speed since so a lot of the cooling water will be leaking out through the water pocket. So as much as hate to do it I have decided to abort launching the boat today and will fix the problem first.
I will try to get it done in the next day or two and launch again on Sunday
Pete

Re: Overheating and shift problems in my 1985 170 Mercruiser

Thought you meant water coming out of the lower. Yeah better to get it right. Good luck.