Normal operating temp merc 305 5.0

[Juniorcarp]

I have 99 SeaRay Alpha 1 gen2 5.0 with efi what is the normal temperature i should see while running i currently run 170 @ all speeeds and 175 at about 4000 rpm is this normal ?​

 

[spdracr39]

Re: Normal operating temp merc 305 5.0

Mine runs at 150-160. I would consider changing the impeller and make sure it has the correct thermostat. If you don't know when the impeller was changed last I would have that done for sure.

 

[Juniorcarp]

Re: Normal operating temp merc 305 5.0

Had the impeller done this spring and changed the circulating pump also changed the two sensors at the thermostat housing !

 

[Oshkosh1]

Re: Normal operating temp merc 305 5.0

Don't get to enamoured with what that gauge is telling you. Not the most reliable intrument. 170/75 is fine...especially knowing the impeller/pump/sensors are new.

My gauge reads 190 or so...but using an IR thermometer says it's reading about 30deg too hot, so I'm around 165/70. Normal...and I've replaced the same three items recently. Ordered a new gauge too...just haven't installed it yet.
Those gauges are guides...NOT precision intruments.

The 150-160 actually seem low if your running hard. MOST engines will operate 15 or so degrees above the thermostat temp.

Lake/River/Sea water injection temp will also affect it...obviously.

 

[ktbarrentine]

Re: Normal operating temp merc 305 5.0

Depends on what t-stat you are running. What's your manual tell you? I know some 5.0s (like mine, 1990) use a 143 deg t-stat....and some (EFI) run a 160 thermostat. Really curious? pop the t-stat out and see what is stamped on it.... then test it in a pan of hot water to confirm it is working as designed. That's an easy start.

 

[spdracr39]

Re: Normal operating temp merc 305 5.0

Mine has a 160 and never runs hotter than 165 (accuracy confirmed with IR thermometer). I rarely run for extended periods at higher than cruise speed but in short bursts it doesn't go up. I have always thought that was unusual but since I verified it I don't worry about it.

 

[Oshkosh1]

Re: Normal operating temp merc 305 5.0

I rarely run for extended periods at higher than cruise speed

Shouldn't you change your "handle" to something other than "Spdracr" then??

 

[Juniorcarp]

Re: Normal operating temp merc 305 5.0

I installed a 160 Tstat if i remember correctly this spring .

 

[Bondo]

Re: Normal operating temp merc 305 5.0

I installed a 160 Tstat if i remember correctly this spring .

Ayuh,.... If you don't know when the impeller was changed last,.....

Change it now...

It's a bi-annual thing...

 

[Oshkosh1]

Re: Normal operating temp merc 305 5.0

Had the impeller done this spring and changed the circulating pump also changed the two sensors at the thermostat housing !

He DID replace his impeller...apparently unsure about the T-stat.

 

[Bondo]

Re: Normal operating temp merc 305 5.0

He DID replace his impeller...apparently unsure about the T-stat.

Sorry,... Speed readin' again...

 

[Juniorcarp]

Re: Normal operating temp merc 305 5.0

Well I took it out and drove it @ 4200 rpm @ approx 55-60 kmh for about 24 km and it never really moved off the 170/175 range . Started @ 170 under load went too 175 and held .... I trolled for some Wally ( caught one) while doing that it went back down to 170.

Even though I did the impeller last season when I get my bellows done this year I will have the housing and impeller changed again for 110$ part Ill do it cooked heads are no fun I went through that already !

Any other advice I surely appreciate thank you !

 

[Oshkosh1]

Re: Normal operating temp merc 305 5.0

I don't know what the problem is...170/175 is NOT too hot.

 

[Juniorcarp]

Re: Normal operating temp merc 305 5.0

I don't know what the problem is...170/175 is NOT too hot.

To be fair I did ask if it was normal !

 

[ktbarrentine]

Re: Normal operating temp merc 305 5.0

Even though I did the impeller last season when I get my bellows done this year I will have the housing and impeller changed again for 110$ part Ill do it cooked heads are no fun I went through that already !

$110? Parts AND labor for that?? No too shabby these days. I do mine once a year, for about 50 bucks DIY (parts and oil, including bell housing gaskets, etc.). It's theraputic.

 

[thumpar]

Are those two sensors the same? I'm assuming they are both temp switches, but I'm not 100% sure. Thanks.

You should open up your own thread instead of posting on a 7 year old one.

One is a sensor for the gauge and the other is a switch for the alarm.