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1998 4.3 Mercruiser running temp

M

MPugh

New member
I have boat that has a 98 4.3 mercruiser. Last year my alarm went off for high temp it was right at 205. I shut the engine off and let it cool down then restarted. It slowly started going back up so I parked it and replaced the impeller in the foot. It still looked brand new but it had been about 3 years since I changed it. When I tried it again it didn't over heat but it would get up and run about 180 at idle or down river. When you would stop the temp would creep up to 195 but then it would go back down to 180. I then changed the thermostat it had a 160 deg in it so that is was I put back. Still same problem. This year after looking at the engine I saw that the weep hole had a little bit of water weeping out of it on the front circulating pump. So i changed that. When I tried it again it would do the same warm up to 180 then creep up to 195 after i had been running it down river and would stop and let it idle but it would go back down or I could take it out of gear and rev it up a little then it would drop back to 180 quicker. I had not really paid attention to the temp gage before this other than making sure it was not over heating so I don't know if this is normal. I thought about changing the temp sending unit to see if that might be a little out of whack other than that i could use some help. So far I used all mercruiser parts also so no weird aftermarket parts used.
 
Suggestion:
Remove the exhaut elbows and examine the seawater transfer ports in both the manifolds and elbows.
If rust scale restricted, clean them out.


.
 
RicardoMarine said:
Suggestion:
Remove the exhaut elbows and examine the seawater transfer ports in both the manifolds and elbows.
If rust scale restricted, clean them out.


I will check that this weekend when i go back to the river. The only problem is I think I have the one piece manifold not the two piece with the exhaust elbow.
Click to expand...
 
When you replaced the impeller did you also replace the gaskets or the pump base?

If there is a 1. gasket torn or 2. the large rubber slinger (sits on top of the water pump housing) then 1. water can leak out of pump housing or 2. exhaust can get sucked into the pump.

Has the impeller ever broken apart in the past and you did not find all the impeller pieces? Is it possible that the power steering cooler is plugged up?


Other wise it is this way...

you need clean fresh water coming in and all that water must get out......so it is either a incoming issue or a out going issue.

Last maybe the thermostat...what temp is it? If it is 160 then you will normally run between 170 and 180
 
kghost said:
When you replaced the impeller did you also replace the gaskets or the pump base?

If there is a 1. gasket torn or 2. the large rubber slinger (sits on top of the water pump housing) then 1. water can leak out of pump housing or 2. exhaust can get sucked into the pump.

Has the impeller ever broken apart in the past and you did not find all the impeller pieces? Is it possible that the power steering cooler is plugged up?


Other wise it is this way...

you need clean fresh water coming in and all that water must get out......so it is either a incoming issue or a out going issue.

Last maybe the thermostat...what temp is it? If it is 160 then you will normally run between 170 and 180
Click to expand...
Replaced gasket, slinger and base bought whole kit. The impeller was still all together no pieces were missing. The impeller has never come apart in the past always together when replaced. It has a 160 thermostat it is running about 180 to 185 the whole time you drive it. It will creep up to 195 after you run it and go to idle but it comes back down to 180. If you rev the motor up a little with it out of gear it will go down quicker. How do you check the power steering cooler to see if it is clogged up? Thanks for the help
 
Check out the water hose between the gearcase and the transom assembly. These will sometimes develop a flat spot and restrict water flow.
 
That is not that abnormal for 160 stat.....a 143 stat runs at 150 degrees, so I would expect a 160 to run about 170 or soon the gage.

the power steering cooler is attached to the power steering line..follow both the high and the low pressure lines. I believe it is in the low pressure line.

It is rare for this to clog when not in weedy or sand or dirty water......


If your gage is off by ten degrees then that would explain the higher than normal temps.
 
kghost said:
That is not that abnormal for 160 stat.....a 143 stat runs at 150 degrees, so I would expect a 160 to run about 170 or soon the gage.

the power steering cooler is attached to the power steering line..follow both the high and the low pressure lines. I believe it is in the low pressure line.

It is rare for this to clog when not in weedy or sand or dirty water......


If your gage is off by ten degrees then that would explain the higher than normal temps.
Click to expand...
Thanks for the input. I am going to check the engine temp with a IR gun tomorrow and see if the gage is off any. Also going to check the hoses to make sure none are restricted. This just all of a sudden started it was no gradual thing I am hoping it is just the gage or possibly the sending unit.
 
makomark said:
check the exhaust elbows with your IR gun....when was the last time they were changed?
Click to expand...

Checked everything today. I was getting good flow through the power steering cooler going to the motor. Took IR gun and checked temp. The gauge would read 180 to 185 and the IR gun showed the engine all around the the water pump and thermostat was at the highest 165. So I am going to check the sending unit and gauge now. Also I only have the one piece exhaust manifolds so I don't have the elbows to check. The only thing I did find was the starboard side exhaust manifold was about 25 degrees hotter than the port side.
 
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