1993 mercruiser 4.3 overheating

[Bill Rod 71]

Hey Everyone,

I'm new to the forum and new to owning a boat.
This is what i got going on. I bought a 1993 18 ft Celebrity 4.3 Mercruiser w/ 4bbl. I haven't had the boat on the water yet have only owned for a few weeks. I was running the boat with the ears on and it started to overheat. So i pulled the thermo which was in bad shape. While I had the thermo out I noticed a hole in the timing chain cover. Pulled the water pump to change the cover and noticed the water pump (recirc) had been leaking. Yea I know! So far owning a boat has been great. LOL. Luckily I don't mind turning some wrenches. So I have installed a new water pump, timing chain cover, and thermo w/new sleeve and rubber o-ring. Boat is running fine but temperature gauge is getting to 225 degree before thermo opens and then gauge goes back down to 150 degree. Then repeats. The risers are getting pretty warm/hot. Not so hot that I can't touch them but hot enough i wouldn't leave my hand on them long. Plenty of warm water coming from bottom of out drive so I assume the water is circulating through the engine. Boat had been sitting for 6 months or so before I purchased. I'm thinking maybe the gauge or sending unit is not working properly but just wanted to get some opinions first. Thanks

 

[cr2k]

Re: 1993 mercruiser 4.3 overheating

When was the impeller last changed? If you don't know we MUST assume it is time. Should be changed every other year if the boat is used or not. What thermostat did you put in it? Should have a 143* I believe. Impeller in in the drive, on top of the lower with the vertical drive shaft going through it.

 

[MarkSee]

Re: 1993 mercruiser 4.3 overheating

Welcome to IBOATS.

If you can't leave your hands on the risers then you have an issue that needs attention before necessarily worrying about a gauge or sending unit.

Do you have an official Merc manual? If not, you need to have access to that information so check out the "Adults Only" section for how to browse one online but first:
Post the engine and drive serial numbers so folks can figure out exactly what configuration you have. Adding that information to your signature is ideal.

Mark

 

[Bill Rod 71]

Re: 1993 mercruiser 4.3 overheating

Thanks for the replies.

cr2k - I have no clue as to how old the impeller is and yes thermo is 140. Atleast that's what the parts guy referred to it as. Said there were two for my engine. 140 and 160 gave me the 140.

Mark - I do not have manual but i have been able to locate pdf file whenever i need to. Haven't saved a copy don't know why prob be eaiser than continuing to google it each time. Where would the serial numbers be located on eng and outdrive. I guess I could search that myself. I'll find them.

I did pull the risers tonight. They were pretty clogged. So in the process of getting the trash out of them now. Also noticed one flapper is missing completely (flapper, rod and the rubber grommmets) and other side is half gone. I'm going to guess but I guess it's possible they could be somewhere down in the y pipe. Any suggestions on checking the y pipe for the missing flapper pieces?

So I'm going to get the risers cleaned out install new flappers and see what happens.

Here are a few pics of the boat. PO didnt pull drain plug and engine compartment filled with rain water including the engine. Drained the water and changed the oil several times, rebuilt the carb. Other than the slight overheating motor sounds good. Got it for $1300.00

Thanks again for the replies

 

[MarkSee]

Re: 1993 mercruiser 4.3 overheating

Where would the serial numbers be located on eng and outdrive. I guess I could search that myself. I'll find them.

I did pull the risers tonight. They were pretty clogged. So in the process of getting the trash out of them now. Also noticed one flapper is missing completely (flapper, rod and the rubber grommmets) and other side is half gone. I'm going to guess but I guess it's possible they could be somewhere down in the y pipe. Any suggestions on checking the y pipe for the missing flapper pieces?

The engine s/n is usually on a tag down by the starter if there is no supplemental tag on top of the engine somewhere.
The drive s/n is usually on the top half on the port side; assuming it hasn't worn away but the guys here with access to Merc software can usually discover other stuff with the engine s/n.

Might want to take a good look at the starter while you're down there if it had been under water.

Sometimes if risers are plugged then the exhaust manifold may be in similar shape or about to be.
Be sure to use only OEM gaskets as some folks have found the aftermarket ones to not quite be up to par with Merc ones.

Hopefully the flappers have worked themselves out but while you have access to the Y pipe, raise the drive see if you can run something through it going both directions.

Quite a nice lookin' rig for only $1300.

Mark

 

[series60]

Re: 1993 mercruiser 4.3 overheating

Hey Everyone,

I'm new to the forum and new to owning a boat.
This is what i got going on. I bought a 1993 18 ft Celebrity 4.3 Mercruiser w/ 4bbl. I haven't had the boat on the water yet have only owned for a few weeks. I was running the boat with the ears on and it started to overheat. So i pulled the thermo which was in bad shape. While I had the thermo out I noticed a hole in the timing chain cover. Pulled the water pump to change the cover and noticed the water pump (recirc) had been leaking. Yea I know! So far owning a boat has been great. LOL. Luckily I don't mind turning some wrenches. So I have installed a new water pump, timing chain cover, and thermo w/new sleeve and rubber o-ring. Boat is running fine but temperature gauge is getting to 225 degree before thermo opens and then gauge goes back down to 150 degree. Then repeats. The risers are getting pretty warm/hot. Not so hot that I can't touch them but hot enough i wouldn't leave my hand on them long. Plenty of warm water coming from bottom of out drive so I assume the water is circulating through the engine. Boat had been sitting for 6 months or so before I purchased. I'm thinking maybe the gauge or sending unit is not working properly but just wanted to get some opinions first. Thanks

Forget about the gauge for now. The manifolds/risers are too hot because of restricted water flow. Drain the outdrive oil then drop the lower unit and change the impeller, being sure everything is installed correctly as per the correct manual for this drive (impeller is located in the bottom half of the outdrive). Be aware of the quad ring gasket which is the only gasket between the upper and lower halves of the outdrive. It should be located on the port side of the bottom half and is about a 1/4" in diameter and sits in a small recess. This o-ring seals the oil galley between the two halves. While you are there pull the upper half of the outdrive and check the exhaust outlet in the gimble for flapper parts. With the top half off check the bellows and water supply hose. Bad drive shaft bellows can sink the boat. It's imperative to get all the flapper bits out to insure proper water/exhaust flow. Scrape and chip as much crud out of the manifolds and risers as you can. Some folks have them media blasted. Pay special attention to the riser where the exhaust and water mix. That area is most susceptible to build up. Use only Merc riser gasket between the riser and the manifold. Don't use cheapo aftermarket gasket here! Be sure to install this gasket with the proper orientation.

​

I use an IR temp gun to keep an eye on my ole' 305 manifold/riser temps. Each side usually run in the 120-130? temp range but are never the same.

Take the time to do this job right or you will be doing it again!
Oh one more thing - take lots of pictures for reference and posting here. We can't rely on our crystal balls so your pictures will be of great help when you need more advice

 

[Bill Rod 71]

Re: 1993 mercruiser 4.3 overheating

Thanks for the advice Series. I installed new flappers and reinstalled the risers this evening. Still the same situation. Heats up to 225 and then back down to 150. I got the risers pretty clean by just scraping. The risers are now staying pretty cool the only time I've noticed them getting hot is when the gauge starts to creep back down to 150. I assume this is from the thermo opening and flushing the hot water out of the engine? The risers cool back down pretty quick. For the most part I can keep my hands on the risers the entire time the engine is running.

The flappers seem a little noisy like their flapping back and forth in the y pipe. The starboard side is noisier than the port. Is it normal for the flappers to make any noise? Also the water draining from starboard side at bottom of out-drive doesn't seem to have as good of a flow as the port. I guess I could have installed them wrong but appeared to be only one way to put them in. Will try to post pics of flappers tomorrow.

So I guess the next thing is to pull the out drive change the impeller and look for old flapper pieces.

 

[Bill Rod 71]

Re: 1993 mercruiser 4.3 overheating

Might want to take a good look at the starter while you're down there if it had been under water.

Thanks again Mark. And yea starter was first thing I had to change. Luckily I found a used one in good shape for 45.00. Like I said to Series I got the risers pretty clean. Still same prob going on. So moving to the out-drive to get to the impeller. Need to take a break from the money spending. Wife was already mad that I bought the boat plus another 300 in parts. Had to camp out on the couch a few nights from the purchase

 

[Maclin]

Re: 1993 mercruiser 4.3 overheating

It kind of sounds like the thermostat is not in quite right, or a check ball or something is missing in the thermo housing maybe.

 

[Bill Rod 71]

Re: 1993 mercruiser 4.3 overheating

It kind of sounds like the thermostat is not in quite right, or a check ball or something is missing in the thermo housing maybe.

I installed the thermo as u would in a car. If I remove the top plate on the thermo housing and look down through it the spring for the thermo is on the bottom side facing down towards intake manifold.Thought that was how the old one came out. Does this sound correct?

Check ball? Only thing that I seen when I changed thermo was: thermo, rubber o-ring, and a plastic sleeve.

 

[Stamey]

Re: 1993 mercruiser 4.3 overheating

I don't see any check balls in your system, if I'm looking at the right diagram, so that probably isn't applicable.
http://www.mercruiserparts.com/Show...=125&bdesc=STANDARD+COOLING+SYSTEM(DESIGN+II)

In a system with check balls they keep the water from flowing to the exhaust elbows at idle, to force the water through the engine instead, and open at higher RPM when they can feed the engine and the elbows due to higher flow, and because at higher RPMs the elbows need more cooling. I encountered this on my 1983 305, where they were missing and the engine consistently overheated at idle bot cooled right down at higher RPMs.
I suppose a big question as to whether you need check balls or not would be if you have water soses going directly into your exhaust elbows. I'm not referring to the ones that go into the manifolds from the bottom, as from the diagrams, two different designs were used in your year, and one has hose going to the front of the elbows, the other does not.
In your case, I swear it sounds like the thermostat is sticking, because while the temperature will normally rise a *little* over the thermostat's setting, 10-15 degrees, then drop down when the thermostat opens, it sounds like yours is waiting much longer to open. That's all I can think of for this particular design. Water flow restriction will increase the temp at the elbows, but will also increase engine temp, as that's how all water exits.

Chris

 

[Bill Rod 71]

Re: 1993 mercruiser 4.3 overheating

I don't see any check balls in your system, if I'm looking at the right diagram, so that probably isn't applicable.
http://www.mercruiserparts.com/Show...=125&bdesc=STANDARD+COOLING+SYSTEM(DESIGN+II)

In a system with check balls they keep the water from flowing to the exhaust elbows at idle, to force the water through the engine instead, and open at higher RPM when they can feed the engine and the elbows due to higher flow, and because at higher RPMs the elbows need more cooling. I encountered this on my 1983 305, where they were missing and the engine consistently overheated at idle bot cooled right down at higher RPMs.
I suppose a big question as to whether you need check balls or not would be if you have water soses going directly into your exhaust elbows. I'm not referring to the ones that go into the manifolds from the bottom, as from the diagrams, two different designs were used in your year, and one has hose going to the front of the elbows, the other does not.
In your case, I swear it sounds like the thermostat is sticking, because while the temperature will normally rise a *little* over the thermostat's setting, 10-15 degrees, then drop down when the thermostat opens, it sounds like yours is waiting much longer to open. That's all I can think of for this particular design. Water flow restriction will increase the temp at the elbows, but will also increase engine temp, as that's how all water exits.

Chris

This what mine looks like

 

[Bill Rod 71]

Re: 1993 mercruiser 4.3 overheating

Also does this look correct. I've been looking at different impellers and have never seen one with the curled blades. If I straighten the blades it won't fit in the housing. Was thinking maybe wrong size?
Best I can give on the out drive is that the boat is a 1993 celebrity, Alpha one out drive, I found a serial number but it doesn't appear to be correct. Nothing comes up when I search for it. 00865200. Maybe I read it wrong. It's pretty Faded.

Can't quite make out the number on the impeller but the best I can see is J17784, but that search turns up no results.

Thanks for any help

 

[MarkSee]

Re: 1993 mercruiser 4.3 overheating

That's what the impeller is suppose to look like.
No fins are missing or appear to be broken so that's a good thing.
An OEM impeller should have a part number similar to 47-43026T

By reading your posts it seems you're getting a little closer if you can keep your hands on the risers longer than before but as you can tell, there's still an issue somewhere.

Mark

 

[Bill Rod 71]

Re: 1993 mercruiser 4.3 overheating

That's what the impeller is suppose to look like.
No fins are missing or appear to be broken so that's a good thing.
An OEM impeller should have a part number similar to 47-43026T

By reading your posts it seems you're getting a little closer if you can keep your hands on the risers longer than before but as you can tell, there's still an issue somewhere.

Mark

Thanks Mark. Was hoping it was going to be that impeller. Guess I can try a new sending unit and/or gauge.

Does that impeller look like it's in the housing correct? It fell out and I don't remember which direction the blades were curved.

Does my explanation sound right about the risers getting a little warmer after the thermo opens and then cooling back down?

 

[NHGuy]

Re: 1993 mercruiser 4.3 overheating

So have you taken off all the hoses and inspected the hoses and the thermostat housing for debris? I'd do that if you haven't yet. On the thermostat housing make sure the inner chambers are all clear. It will be rusted on the inside, knock down any big rust chunks to be sure the water can go where it's supposed to.
With the drive off remove the hose at the feed to the thermostat and backflush it. Water should flow right out, if you are inquisitive you could put a strainer under the inlet at the bellhousing to see what it catches.
The tube that goes through the transom is the smallest diameter point and it has bends, that could have caught something.

Paraphrased from my alpha 1 manual:
Exhaust elbow water outlet hole obstruction
Seawater inlet hose kinked or collapsed
Cooling system obstruction, casting flash, sand, salt, rust
Water hoses mis-connected at distribution block
Bell housing to drive unit o-ring missing or damaged
Bell housing to transom hose kinked or blocked

Does your cooling system feed the motor, the exhaust elbows and the exhaust manifolds? Or just the motor and the exhaust manifolds?

 

[Bill Rod 71]

Re: 1993 mercruiser 4.3 overheating

Thanks for the replies and sorry it took me so long to post back but, it seems like the overheating was the impeller. Installed a new one and stays around 150-170 or so degrees.

Thanks again