Mercruiser 7.4 temp rising

[msd58]

1998 7.4 mercruiser normal operating temp around 170*
second to the last last time out temp rose up to 195*. Never did that before. Manifolds & riders new, heads redone, RWC & Bravo III. Last run on boat was in Nov temp seemed OK.

Any thoughts?

 

[Don S]

Re: Mercruiser 7.4 temp rising

When was the last time the raw water pump impeller was replaced?

 

[msd58]

Re: Mercruiser 7.4 temp rising

I'l try to find out via old reciepts. It could be its a been a very ling time or not at all.

 

[Don S]

Re: Mercruiser 7.4 temp rising

Well, better start there, they should be changed every other year. If the vanes break off, they will get stuck all through your engine.

 

[msd58]

Re: Mercruiser 7.4 temp rising

OK. One more question is there strainer coming off the thru-hull for the water pump that might be cloged?

 

[Bondo]

Re: Mercruiser 7.4 temp rising

Mercruiser, I don't believe puts 1 there,......

But that doesn't mean 1 hasn't been Added.......

 

[Don S]

Re: Mercruiser 7.4 temp rising

I don't know if you have one or not. Look in your bilge and see. I've seen them with and without. Do you have water pickup from the drive or a thru-hull fitting? If something is plugged up, it could damage the impeller also. Those impellers are a maintenance item that gets replaced every few years. If you don't know how long it's been in there, then it's too long.
The impellers are the FIRST thing you check on a boat when the temp starts going up. They can be damaged in so many ways.

 

[msd58]

Re: Mercruiser 7.4 temp rising

I'll check for the thru-hull. I saw one it may be for the a/c. 1998 Sea Ray cruiser.

 

[Bondo]

Re: Mercruiser 7.4 temp rising

When the Impeller is changed,....
Make Sure you Find All the Missing Pieces.....
A Mising Vane will raise all kinds of havoc, restricting the water passages.....

 

[imported_rosco]

Re: Mercruiser 7.4 temp rising

raw water pump impeller, thermostat, or some blockage in the drive pick up.

all of which are dirt cheap to fix. BTW, mecruiser usses a 180 degree thermostat. it should run a little cooler that that at cruise, say, in the 170 to 175 range, but 180 at idle is not uncommon.

195 is bad.

the sea water pump impeller should be replaced yearly. would suggest the same with the thermostat. both are cheap, and it just doesnt make any sence to roll the dice with them.

remove the hose from the feed side of the sea water pump, its the thing with the pully down at the bottom of your engine on the starbord side, possibly with a fuel pump sitting on it. then flush water through the hose side and blow out the drive pick up.

i would check those three things first. the only other thing it could be is the water pump on the engine itself. i have seen the impellers completly rusted off before. if the first three dont fix it, might want to check there.

one more thing, is it a closed cooling system? if it is, its possible your exchanger is going bad. it is common. one of the reasons people dont bother with them unless they have the type of boat you have to cut a hole in the deck to replace an engine.

 

[msd58]

Re: Mercruiser 7.4 temp rising

Its RWC

 

[Don S]

Re: Mercruiser 7.4 temp rising

Its RWC

Yes, you stated that in your original post.
The thermostat for Mercruiser raw water cooled engines are 160° NOT 180 as mentioned, and every other year for an impeller change us fine, not necessary to change yearly.

 

[Don S]

Re: Mercruiser 7.4 temp rising

one more thing, is it a closed cooling system? if it is, its possible your exchanger is going bad. it is common. one of the reasons people dont bother with them unless they have the type of boat you have to cut a hole in the deck to replace an engine.

Do you just make this stuff up as you go along rosco? You have to because I've never heard this from anyone else, and you are also the only one that has ever come up with Merc using 180° thermostats.
And the circ pumps only go away with the impeller rusting off when some one puts an automotive pump on a raw water cooled engine and boats in salt or brackish water.

 

[bruceb58]

Re: Mercruiser 7.4 temp rising

You have to say something about rosco...almost everyone one of his posts has at least one thing wrong in it.

He is always wrong...that is what is so right about him.

 

[Don S]

Re: Mercruiser 7.4 temp rising

You have to say something about rosco...almost everyone one of his posts has at least one thing wrong in it.

He is always wrong...that is what is so right about him.

But the poor new guy with one post doesn't know that, that is the sad thing about all his miss-information.

 

[Bondo]

Re: Mercruiser 7.4 temp rising

Ayuh,............

I'm Really starting to Believe that Trog has moved to South Florida.................:% d

 

[Don S]

Re: Mercruiser 7.4 temp rising

I'm Really starting to Believe that Trog has moved to South Florida................. ">

I was thinking that myself....... shudder...... Could you imagine the rosco/trog tag team of wierd going on here at iboats ??? Scarry

 

[imported_rosco]

Re: Mercruiser 7.4 temp rising

Do you just make this stuff up as you go along rosco? You have to because I've never heard this from anyone else, and you are also the only one that has ever come up with Merc using 180° thermostats.
And the circ pumps only go away with the impeller rusting off when some one puts an automotive pump on a raw water cooled engine and boats in salt or brackish water.
------------------------------------------------------------

my mercruiser 502 EFI has a 180 thermostat. my twin 454 trs in my donzi had 180 thermostats. infact, my twin volvo penta 502,s i replaced my 454s with had 180 thermotats. i have a drawer full of them. replace them annually with my raw water impeller. the normal operating tempature is like he said, around 170 to 175 degrees.

and i have replaced the factory mercruiser water pump on one of my 454,s when it was 8 years old with the impeller vanes completly corroded off.

its not likely in his case, but like i said, if the other stuff doesnt work, its worth looking at. it is possible.

i dont understand why you people would not want him to check it out if the other 3 things dont pan out for him, or is this some type if pecking order turf war about who can give advise?

bah, my boats running again, ill go play with my chartplotter.

good luck,

 

[Don S]

Re: Mercruiser 7.4 temp rising

Like I said in another post.

You obviously have a lot of political speech making experience. You make very long replies that have few documented facts, and reference things you obviously no little about, including a lot of really false/incorrect information, and never really say anything constructive, useful or helpful

 

[Bondo]

Re: Mercruiser 7.4 temp rising

my mercruiser 502 EFI has a 180 thermostat. my twin 454 trs in my donzi had 180 thermostats. infact, my twin volvo penta 502,s i replaced my 454s with had 180 thermotats. i have a drawer full of them. replace them annually with my raw water impeller. the normal operating tempature is like he said, around 170 to 175 degrees.

Maybe That's Why your south Florida motors keep Rotting out on You,...........