Need advice for 1982 IMP Mercruiser 5.0 runs hot

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Old 06-16-20, 07:31 PM
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Need advice for 1982 IMP Mercruiser 5.7 runs hot

Replaced the impeller couple times still will not pickup fluid / I back flushed it several times so I think no blockage in the lines. Could it be the water pump on the motor ? The pump on the motor is not leaking, not loose, makes no noise ? Thermostat is ok.
 

Last edited by moon_phaze; 06-16-20 at 10:26 PM.
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Old 06-16-20, 08:58 PM
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Welcome to the forums.

When you removed the old impeller...... where the vanes missing ?
If yes...... more than likely they are stuck in one of the lines or in one of the coolers.
There are different Mercruiser setups.
Without an exact model I don't know everything in the cooling loop.
 
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Old 06-16-20, 09:13 PM
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Yes the fins were gone on the first impeller we pulled out. Second one worked for 20 minutes or so, and the water that was being expelled was full of air bubbles. Next day started it up and nothing. So today we dismantled it again, double checked all the gaskets o rings etc. Still the impeller will not pickup . Where or what are the coolers ? mercruiser 260 pre alpha I believe.



 

Last edited by moon_phaze; 06-16-20 at 09:28 PM.
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Old 06-17-20, 11:29 AM
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Old 06-17-20, 11:38 AM
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Yes.... a good video.
I was checking around into your problem.
 
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Old 06-17-20, 12:20 PM
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mercruiser 260

Thx Pete, my first boat > crash course 4 real
 
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Old 06-17-20, 12:45 PM
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I've had several boats with Mercs. Never had an overheat problem.

I'm checking around on yours. There are many things that could cause your problem.
I'm seeing....
incorrect impeller.
rusted or clogged exhaust manifolds.
Parts of the impeller stuck in system.
I would think you need to make sure water can flow thru each hose.
 
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Old 06-17-20, 01:38 PM
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Judging by your photos I assume your boat has been used in freshwater. I had a overheating problem in one of my boats but it lived in salt water and the engines were raw water cooled so marine critters and sand had clogged some passages after it sat for a long period without being run. Your engine appears similar to mine were and is probably raw water cooled as well since I don't see a heat exchanger (there is at least one for the oil though and for power steering).

I'd also check the water flow to and out of the oil cooler/heat exchanger. If you have power steering I'd check it's water flow as well.

Have you checked the thermostat? It wouldn't hurt to check for water flow out of the six cooling hoses that go to the exhaust system at their outlet end and start the engine and see if you get good flow.

Here is a very general diagram. Not of your engine but it will give you an idea of how the cooling system works.

 
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Old 06-17-20, 08:30 PM
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Geez this is crazy. I disconnected the hose from engine oil power steering cooler started it up and still no water. Looking in the oil cooIer we did not find any rubber fins I expect the impeller is the problem. We back flushed thru the oil cooler and water came out the intake ports by the prop. We run water thru all hoses and everything circulated. No thermostat in housing although I will install a new one once water is circulating. Maybe the impeller is backwards ?? but I did place it in the housing as seen several vids in youtube. Thx for the diagram .... go figure
 
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Old 06-17-20, 08:37 PM
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Make sure the impeller fits correctly in the housing. Apparently there are different sizes.
 
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Old 06-17-20, 08:43 PM
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Old 06-17-20, 09:32 PM
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Yes..... pretty complicated. Not to mention the use of plenty of plastic that can melt and distort.
 
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Old 06-17-20, 10:03 PM
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Water Pocket Cover Kit < Is that what the piece up in the upper part where you stab the shaft and water tube in ? ( after impeller replaced and preparing to bolt together ). Cannot seem to find but a few for sale. Maybe I need other key words to search ? Hey thx guys .. much appreciated your help
 
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Old 06-17-20, 10:14 PM
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Amazon has some kits listed they may be helpful.
Mercruiser parts
 
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Old 06-18-20, 06:24 AM
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You may be air bound. There should be a small screw on top of the impeller housing that you need to loosen before start-up. This is an air bleed screw. Once you start up and water is flowing around the screw threads, tighten it back down and you should be good to go. If this doesn't fix it and your using a poly impeller, switch back to rubber, or an impeller with less fins. both the poly and the too many fins can cause cavitation.

Good Luck
 
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Old 06-18-20, 01:31 PM
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Ok, is this the air bleed screw ?
 
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Old 06-18-20, 02:29 PM
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Maybe. If that's your impeller housing then probably.
 
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Old 06-18-20, 03:54 PM
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Old 06-18-20, 04:26 PM
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I think I will remove the one in the housing and replace it. I have Merc service manuals volume 1 and 2 and can find nothing on this part > Last resort ... water went thru the system bypassing the impeller starting at motor water pump. Plastic like you said PJMAX. I do not think I can get that bleeder screw loose without getting out the cuttin torch or a big sledge hammer. I have soft rubber 6 fin impellers, and 2 more new ones on the way. what a deal ... buy a boat and you got yourself a big hole in the water to toss your money in

 
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Old 06-19-20, 05:31 AM
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The two happiest days of your life. The day you buy a boat... and the day you sell it.
 
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Old 06-19-20, 10:42 AM
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WD-40 won't help you loosen a rusted part.
You need to use Liquid Wrench or PB Blaster penetrating oil.
 
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Old 06-19-20, 11:05 PM
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It has sure been a learning process understanding how a boat functions. Traded a watch for the boat. Paid $100 for the watch. Boat had a total rebuild, not been in the water more than 6 hours. Altogether I put 400 - 500 bucks in it. Guess I shouldn't complain. >> liquid wrench it is > I get some / thx 4 the heads up
 
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Old 06-21-20, 01:49 PM
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so .. i found a couple oblong rubber pieces below the stern on the ground. Wondering what the heck ? I see what looks like exhaust smoky film on the rubber ... so I thinking they came out of exhaust tube. A big duh ! Shutters for anti hydro-lock. So we have new shutters ordered


John Casor1 month ago (edited)
how you clean out that engine is easy cost you $10 ..... just use one gallon of DIESEL FUEL flush it out by no spark to plugs so will not start. and spin on a new oil filter and crank over engine for 5 mins off and on so starter will not get super hot so like 30 sec each time until you hit 5 mins... then drain it out all the diesel fuel and install a new oil filter and new oil... i do this for a living and i have done this many times and it cleans out everything all water and old oil is gone...



https://www.youtube.com/watch?v=8DEVHcoFXNA

https://www.youtube.com/watch?v=da1wIQ3_eqM&t=122s
 

Last edited by moon_phaze; 06-21-20 at 02:17 PM.
  #24  
Old 07-17-20, 11:59 AM
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Looks like A pic of an Old Merc ONE. or older. It is not an air bleed. That is the air vent when you re fill the gear case.
 
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