1973 mercruiser 140 h.p overheating

[tatt2oed]

Just purchased this boat. It has the the gm 4 cyl with mercruiser outdrive, the boat runs great but i noticed it wanted to run warmer than I like, not actually overheating but right at the verge of it. I put the muffs on and ran the boat, the temp stays low like it should. Any ideas? is it the impeller?
Thanks in advance to anyones advice,
Scott

 

[thrillsea-ker]

Re: 1973 mercruiser 140 h.p overheating

You mentioned that you just purchased the boat.. As a precaution, I would replace the impeller. You never know just when the previous owner last changed it. As a rule of thumb, I change mine every season. It is cheap insurance. Other than that, I would replace the thermostat, that could be worn and not opening when it should. Hope that helps...

 

[tschmidty]

Re: 1973 mercruiser 140 h.p overheating

As said replace the impleller, it is most likely rotted and not pushing water like it should not to mention the bits of it clogging up the flow. You can find cheap kits for around $35. Changing it is a matter of building some kind of simple stand for the drive, a 5/16 and 3/8 allen wrench, wrenches and ratchet. You will want to pick up a couple drive oil screw gaskets and a quart or two of high performance drive lube so you can change the oil since you have to top it off anyway.

 

[tatt2oed]

Re: 1973 mercruiser 140 h.p overheating

The impeller is going to be my project for this weekend. I will let you guys know the result.
Thanks for the input.

Scott

 

[tatt2oed]

Re: 1973 mercruiser 140 h.p overheating

Well,I finally got the time to check the impeller. It actually looks fine and is nice and pliable. It does looks as though the small upper housing may have been a little hot before. The last person in there before me left me a nice broken bolt to deal with. (thanks guy who ever you are!!) So, now it looks like reassembly and some fresh oil then move up the thermostat. Anything else I can look for??
Thanks in advance,
Scott

 

[cr2k]

Re: 1973 mercruiser 140 h.p overheating

I hope you replaced the impeller when you were in there. They can look to be in good shape but not pump well. Replace interval every 2 years.

One thing you need to do is check your heat exchanger for any debris. Often an old impeller blade will get stuck there hampering the flow. You mentioned that the top of the housing looked like it was toasted, needs to be replaced if so.

If you ever pull your impeller and find less then ALL the parts you must look for and remove ALL of them or you will have overheating issues.

 

[tatt2oed]

Re: 1973 mercruiser 140 h.p overheating

Finally attempting impeller replacement today. Any advice? I bought the housing kit that has both housing pieces, gaskets and orings plus the impeller, also bought a new water pocket housing.
which way does the impeller rotate?
Really hoping this takes care of the problem!! The only real problem I found was with the water pocket housing. It looked melted. Also has 1 broken bolt.

Any tips, pointers advice will be greatly appreciated!!
Thanks to everyone in advance
Scott

Ps.
Also, as I was working on the lower unit today I noticed a passageway in the front section of the unit clogged with crud. It leads down to a small opening near the bottom of the outdrive. What is this for? I managed to clean it out and get good water flow through this but was curious as to what this is and could it have been a part of my original overheating problem.

 

[tatt2oed]

Re: 1973 mercruiser 140 h.p overheating

Anyone?

 

[shadetree918]

Re: 1973 mercruiser 140 h.p overheating

Not sure what that small hole is either. My exhaust ports up near the top of the transom mount where hot water comes out were completely clogged, keeping hot water in the engine. pulled the hose off the heat exchanger and stuck the garden hose in there to flush them out. Helped my over heating prob. I also flushed all the coolant out with a cleaner and steam cleaned the heat exchanger, tested the thermo stat in hot water on the stove with thermometer, works good. opens right at 160, all the way at about 180.

 

[tatt2oed]

Re: 1973 mercruiser 140 h.p overheating

here is a couple of pics of the area i was speaking of. It was packed with crud, took me a while to get it cleaned out!

 

[Bt Doctur]

Re: 1973 mercruiser 140 h.p overheating

normal for it to get jammed up with mud and sand, it`s just a cavity that is supposed to drain from the small hole.the water pocket cover can be a pita. you can test for leakage first by putting water up the copper connecting pipe.they get to look like that from a overheat condition but unless they leak, leave it alone.

 

[tatt2oed]

Re: 1973 mercruiser 140 h.p overheating

Thanks for the input. After reading I decided to leave that bolt alone, stainless is a pain in the a__ to drill!
Going back together in a few, I will let you guys know the results.

 

[fastempo]

Re: 1973 mercruiser 140 h.p overheating

Re: The little hole at bottom of stern drive on starboard side. Yes, that is merely a drain hole for the cavity in front of the shifter shaft. It is a good idea to keep it clean, so the water that does get in to the front cavity will drain, especially if you operate in salt water conditions