1984 4 cyliner mercruiser running hot?

[alan ber]

1984 mercruiser 4 cylinder runs hot when I throttle up?
Self contained cooling

My mechanic is over booked any trying too trouble shoot this issue myself
Weeks ago engine temp started too run hot when I throttle up on plane.
WHen this started too happen I brought boat into a shop I use.
First thought was impellar need too be changed , Was changed last season along with lower unit maintance along with boot, throttle cables, and all hoses.
No more than 20 hours of use
After changing mechanic said really did not have too be changed
Engine gradually getting hot was an indication that impellar had issues.
Putting boat back into water and the same happened.

Boat tied too dock ran at idle an hour and temp stays less than 1/2, which is a little high
Taking out of no wake area, open up and I watch temp needle raise too 3/4 and hotter real fast
Backing off throttle back too idle temp lowers too 1/2 as I slowly return too dock
While at dock, took out thermostat, took out for a spin and ran hot when opening throttle.
Taking boat home, opened heat exchanger and discovered chunks of rubber front end of heat exchanger, Opened back end, no clearance too look but felt no chuncks of rubber . My thinking was an older impellar broke apart working its way into heat exchanger.
Just too make sure impellar is pumping, put rabbit ears on lower unit. removed rubber hose that comes off impellar pump that goes too heat exchanger
Cranked engine a brief second and water pumping strong
Thinking rubber in heat exchanger was the cause I installed everything, took boat out and same, hot when I throttle up.

Calling my mechanic, he feels water level in engine is not high enough. Telling him opening resevar cap water is full.
He feels there is a air pocket in self contained cooling . He feels water is not going all the way down. He said I have too try too burp the cooling system? Said I have too raise boat as high as possible, open pet- **** and let water drop and fill ?

SO fellow boaters put your tinking caps on , what else should I look for.
There is a blockage some were not allowing water too pump properly.
Water pump is not a seperate unit,like on a 8 cylinder engine, on the 4 cylinder spins off of crank shaft and entire front of engine as too come off. Done this a number of times too correct water leakage.

SO what does this sound like.and what should I be looking for ?
I am a weekend warrior and at times I luck out with repairs, but find I buy parts not needed for lack of knowledge

thanks
al in Orlando

 

[Flagtr]

Re: 1984 4 cyliner mercruiser running hot?

I have a 79 Merc 470, similar problem. Have had the impellar repaced. exhaust bellow elbow was leaking, replaced it. Heat exchanger was leaking had it fixed. Took the boat a small lake, ran it slow was fine. I took it to the big lake, ran it a little harder, temp was 160 to 180 or so. Went swimming, and on the way back to the dock, I opened her up and she over heated. No coolant s was sucked from the reservoir. Mechanic told me the reservoir cap could be replaced. I have always thought the thermostat to be suspect. Also, I dont know if exhaust water is coming out the prop. Any other ideas? There is great info on this site! thanks to all!

 

[ENSIGN]

Re: 1984 4 cyliner mercruiser running hot?

If the impeller is ok like you say,Install a clear piece of hose between the transom water fitting and the heat ex changer.Run the boat in the water and look for air bubbles in the line

 

[stonyloam]

Re: 1984 4 cyliner mercruiser running hot?

OK, I do not believe either of the things your mechanic says is your problem. If you have old impeller pieces in there it means that it probably overheated at one time, so IMHO the first thing you need to do is change the entire impeller pump and housing preferably with a OEM Mercruiser unit. I would not worry about any more blockage in the exchanger, the water goes in the front hose so all of the large pieces should be there. The other thing to do is put a garden hose on the exhaust elbow fitting (hose coming up from exchanger) and see if there is free flow out of the exhaust without too much backpressure. You do have it filled with 50/50 antifreeze right? Only mentioned because you mentioned water leaking out of engine pump. Good luck.

 

[alan ber]

Re: 1984 4 cyliner mercruiser running hot?

Thanks Terry
Just prior too reading your response was outside messing around with engine
I happened too remove entire hose from exchanger, power steering cooling system checking for any blockage. Re installing left the end that goes too resevour off, had rabbit ears pumping water, started engine, water was pumping up. What I noticed and here is were I don't have enough experience working with these engines, the elbow goes back too resevior, once hose is off shouldn't water come out of that resevior end? or it just goes in, not out?
I trust this mechanic and I think he has done right by me on other work. He did say he changed impellar, and showed me the old one, but he just showed me the small fans, have no way of knowing if he changed everything. But this has happened too me years ago and once impellar and pump was changed it corrected the problem.
I see on u tube how too change and it looks easy enough.
Problem I have , I jump into these jobs, then if I screw up something, I still go too him too correct.
Here in the Orlando area tons of **** head mechanics or wanna be mechanics that love too screw the public. THis guy has scrap yard of
old mercuriser parts which has helped me greatly. JUst hope he is not blowing smoke up my _____

Will mess around further
thanks

 

[stonyloam]

Re: 1984 4 cyliner mercruiser running hot?

You have two separate systems here. The coolant side and the raw water side. The raw water comes in through the transom, through the voltage regulator, into the front hose on the exchanger, out through the rear hose of the exchanger, up through the p/s cooler, up into the fitting on the exhaust elbow and out with the exhaust, where it cools the exhaust and rubber parts (including the shutters) on the way out. All of the other hoses including the ones going to the reservoir carry antifreeze coolant which is circulated through the closed system. Here is a link to the manual so you can read up on how it works: http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/0 It seems like you still do not have enough fresh water circulating. There is a troubleshooting chart in the cooling section. You can print out the pages you need. Good luck.