What temp should my boat be running at??

[vigil2448]

Okay, so I replaced the impeller, and theromastat, and temp guage on my 1989 4.3 mercruiser. I haven't replaced the temperature sensors.

Now when I run it at idle for about 10-15 minutes, the temp reads about 184 degrees, but will not drop it I give more throttle, neither will it rise. Is 184 degrees seem about right?? the t-stat is 140 degrees!! Any input would be appreciated!!

Also the Starboard side of the boat, the manifolds are super hot, while the port side is a just a little bit hot.

 

[Brentathon]

Re: What temp should my boat be running at??

Sounds a bit high to me, as a 140F T-stat starts to open at 140, and is fully open at 165F.
I would confirm the temp is really what the gauge is showing.
I had a brand new Sierra impeller in mine and it produced low flow, and after much work/money, found that their impeller was defective.

 

[vigil2448]

Re: What temp should my boat be running at??

I just replaced it with a mercruiser factory replacement.

Also the starboard side is super hot on the manifolds, while the port side is just a little hot.

 

[Dsilvers112]

Re: What temp should my boat be running at??

Ive got a 96' 4.3 Mercruiser and it usually runs between 150-160. Id say its running a little hot. I would deffinately fix it before i cracked a head!

 

[Brentathon]

Re: What temp should my boat be running at??

"starboard side is super hot".....that's a very important piece of info that you initially left out. You need to start the typical cooling system troubleshooting process. Learn all about the cooling system, and start investigating probable culprits, etc.
Risers/manifolds, O/D impeller, hoses, T-stat and housing, engine circulating pump, etc. etc.
Good luck.

 

[Kaplooi]

Re: What temp should my boat be running at??

You might have 2 separate problems. The manifold on one side being much hotter than the other might be localized to the t-stat housing if you're lucky. I'm assuming you're year engine means you have an Alpha One Gen I with the spring loaded check ball restrictors on the t-stat housing. It could be that the starboard side check ball is plugged up or something. If so you're not feeding enough water directly to that riser which could cause it to overheat. I know that if both restrictors are too loose they allow too much water to bypass the engine and you can have overheating issues due to a lack of water going into the block.

As for the heat readings being high, if you've eliminated other things as a potential problem do an ohm test on your temperature sender. Any reading significantly out of spec and you can be sure that your gauge is not reading accurately. On mine the ohms were way too low by several hundred ohms and read between 180-190 degrees at idle which I knew was too high (resistance should drop as temps increase). After replacing the sender the temps held steady around 150 degrees on the gauge.

 

[vigil2448]

Re: What temp should my boat be running at??

You might have 2 separate problems. The manifold on one side being much hotter than the other might be localized to the t-stat housing if you're lucky. I'm assuming you're year engine means you have an Alpha One Gen I with the spring loaded check ball restrictors on the t-stat housing. It could be that the starboard side check ball is plugged up or something. If so you're not feeding enough water directly to that riser which could cause it to overheat. I know that if both restrictors are too loose they allow too much water to bypass the engine and you can have overheating issues due to a lack of water going into the block.

As for the heat readings being high, if you've eliminated other things as a potential problem do an ohm test on your temperature sender. Any reading significantly out of spec and you can be sure that your gauge is not reading accurately. On mine the ohms were way too low by several hundred ohms and read between 180-190 degrees at idle which I knew was too high (resistance should drop as temps increase). After replacing the sender the temps held steady around 150 degrees on the gauge.

okay i did replace the t-stat, when I did take it off there was some old pieces from the previous impeller, removed those the pieces, the ball restrictors are spring loaded and appear to work fine. The t-stat housing seems to be the factory and was pretty corroded with some rust but still allows water to travel. Will the build up, restrict a SIGNIFICANT amoount of water, not allowing the manifolds to cool properly??

 

[vigil2448]

Re: What temp should my boat be running at??

sorry I keep leaving things out. Also the riser are nice and cool, but those manifolds are a hot. maybe a restriction between the risers and the manifolds???

 

[Bt Doctur]

Re: What temp should my boat be running at??

http://www.boatfix.com/merc/Bullet/81/81_14.pdf

 

[vigil2448]

Re: What temp should my boat be running at??

okay so with the water running, and the motor running these are what I have felt and believe to be the proper route of water running. I'm assuming that the manifolds are supposed to be hot from the warm water running to them, because they would possibly be damaged it cooled with cold water (i'm only assuming). Again my temp is still at 184 when running, but will never increase, or decrease. I know the temp is a little high, from what other iboaters have explained to me (ideal temp aprox. 165).

I took off the elbows and they seem not to be obstructed by any foreign matter, and the exhaust manifolds seem to be okay (other than a slight crack that the previous owner repaired by jb weld). I've ran the boat for 4 years and have had no problems till now.

 

[vigil2448]

Re: What temp should my boat be running at??

bump...Anyone?? I really wanna take the family out this weekend

 

[Kaplooi]

Re: What temp should my boat be running at??

If the risers are cool but the manifolds seem unusually hot that sounds like you have circulation issues inside the block, which suggests either the circulating pump is on its way out or you have some sort of blockage inside the water jacket in the block. Assuming the temp sender is reading the correct temperature helps corroborate poor circulation in the block. This also assumes the check balls are restricting flow correctly and the proper amount of cold water is entering the block. I also have an '89 4.3 and my risers also stay cool enough to touch so your t-stat housing is 'probably' directing flow correctly. You mentioned that you were able to remove some pieces of old impeller rubber from the t-stat housing so maybe some of it went through. Short of back flushing your block to see if there's any obstructions I suppose the only mechanical thing left to replace is the water pump.

Again, before doing anything I'd do a resistance check on the temp sender to confirm it's within spec. I don't remember the exact resistance, but at room temperature it should read at least a few hundred ohms. On my old faulty sender the resistance was only 77 ohms cold which is way too low.