Temerature readings, how to interpret?

[Theresamarie11]

Temperature readings, how to interpret?

I have twin 350 MAGs, 2002 300 DA. The boat runs very strong. Both temperature gauges say they're running between the 170 and 220 mark (halfway between). Based on what others told me I was worried this was too high so I purchased an infrared temperature meter (again on recommendations). This weekend, while running and warmed up and the gauges reading as above, I ran temp checks on the risers, thermostat housing and water hoses. I found the warmest place the thermostat housings at 158-160 each, the water hoses were a bit below this and the risers were a lot cooler. Does anyone know how to correlate these results? Do they make sense. Are my motors running cooler (160) and not 190 like the gauge would say (although since the gauge has so few hash marks and defined temperatures it's hard to know if it's meant to be linear between the 170 and 220 marks).

If the motors are running 160 degrees, what might cause the gauges to both read high?

Thanks for any insight.

Terri

 

[Scottzzzy]

Mine apparently do the same thing. My surveyor used the heat gun to check everything and simply said they are analog gauges and they can differ slightly because of this. My starboard side is dead on 170, but my port side shows like 180 ish. Sometimes dead on 170 also. I make sure my impellars are changed on schedule and keep and eye on all my hoses. Have you looked inside your risers or manifolds to see if they are closing up from scaling? I am on fresh water so I do not have as much of a problem with this.

 

[Theresamarie11]

Thanks Scotty, it's a little unsettling and I find myself constantly looking at the gauges worried about the temp. I might see if changing one of the temp sensors fixes that reading. I was also wondering if there is some offset from what I measure at the surface versus what might be the temperature inside.

 

[capecodcruiser]

You have to remember that your sensor is sitting in the coolant. You are checking the surface temps. My 350's run approx 180ish with one running a little hotter occasionaly. If you are close the 220 mark, I would be worried. These computer controlled motors run a little hotter, I think 190 at 3500RPM is a safe number. Much deviation higher and some investigation is necessary.

 

[billnpat]

I find my self as Terri constantly watching the temps, both show 170....My starboard ran 190 at sea trial and they changed the riser and impellers and its now 170....

 

[Theresamarie11]

Thanks folks, still trying to understand if there is an offset between liquid coolant and therm housing when looking at temps. I do realize the sensor is in the coolant (raw water in this case).
Also, with respect to the risers. Does the riser water, after it's goes into the riser ever get circulated back or does this just exit the motor with the exhaust? Just wondering how high temperature might mean a riser issue? The impellers were both replaced at the beginning of the season and pump very well best I can tell. I have the merc manual which shows water circulation but hard to tell where the water exits the system.


Thanks,
Terri

 

[dpmulvey]

Mine apparently do the same thing. My surveyor used the heat gun to check everything and simply said they are analog gauges and they can differ slightly because of this. My starboard side is dead on 170, but my port side shows like 180 ish. Sometimes dead on 170 also. I make sure my impellars are changed on schedule and keep and eye on all my hoses. Have you looked inside your risers or manifolds to see if they are closing up from scaling? I am on fresh water so I do not have as much of a problem with this.

+1 right down to the temp readings.

Shy of digital gauges connected to the bus, you cannot be sure of the temps. My mech calls the gauges abouts. You are running about 170 and about 40PSI oil.......

 

[dpmulvey]

Thanks folks, still trying to understand if there is an offset between liquid coolant and therm housing when looking at temps. I do realize the sensor is in the coolant (raw water in this case).
Also, with respect to the risers. Does the riser water, after it's goes into the riser ever get circulated back or does this just exit the motor with the exhaust? Just wondering how high temperature might mean a riser issue? The impellers were both replaced at the beginning of the season and pump very well best I can tell. I have the merc manual which shows water circulation but hard to tell where the water exits the system.


Thanks,
Terri

I believe the RWC engine should run a 160 or 165 degree T'stat. The FWC T'stat is 170 degrees.

As to the cooling water and the risers; It is a one way trip. Into the engine; cool the engine; out via the exhaust manifolds and risers never to be seen again.

 

[Theresamarie11]

Thanks David, I guess I'll be ok knowing my gauges don't really give me anything accurate . I may look at the harness connection and gauge grounds to see if there are any issues there. I'm not clear on what causes the gauge to rise (high or low resistance) to see if bad connections might add to issues.

Also, thanks for the pointers on path for water. I have the manual and have looked at the diagram but honestly, it wasn't entirely obvious to me what path is for cooling and what path is for draining, although none are closed for either operation except for petcocks (blue plugs).
Other gauges on the cluster seem more or less accurate and may peek in there to see what's going on.

The engines just hit 320 hours and yesterday we ran our 300DA, with 3 on board and fully loaded and camper canvas at 48mph on the GPS with just a light headwind and a small ripple. Only for a few minutes mind you, we usually run around 32mph at around 3400 RPM (depending on which tach you look at...they seem to bounce around). Burning $300 of fuel per weekend puts a damper on high speed runs as well....

Terri

 

[Jay Gadsby]

Yeah 160 at the manifold seems a bit high to me. I can usually lay a hand on the exhaust without crying after running. My engine runs at 170 solid now with a new impeller and manifolds and such.

 

[Theresamarie11]

Jay, which manifold are you referring to? If you're talking about the exhaust manifolds I think mine were below 100 degrees (95ish) and I was surprised they were that cool.

Terri

 

[Jay Gadsby]

Ah, my bad I dont generally touch the engine if at all possible, and the thermostat housing is on that list of things I have not touched. Sorry about that mate.

 

[Scottzzzy]

My gauges do flex somewhat, but I too am a slave to the gauges and the fear of too high oil pressure or temps with these analog gauges.

I wonder if anything is different for me as my 340 is CLosed Water Coooled??

 

[Theresamarie11]

My gauges do flex somewhat, but I too am a slave to the gauges and the fear of too high oil pressure or temps with these analog gauges.

I wonder if anything is different for me as my 340 is CLosed Water Coooled??

In an earlier post someone mentioned that you run a little higher thermostat with a closed system. I think the systems monitors are probably the same technology for the same years, standard gauges or smartcraft (which are each different systems).
I try not to be a slave, but it just bothers me the temp seemed high. I'll eventually figure it out.


Terri

 

[dpmulvey]

A Harbor Freight digital temp gun is a great $29 investment. It is great for diagnostics and peace of mind. A big plus to me is once you get a feel for how your engine(s) are running, you can use the dash gauge as a point of reference as opposed to an absolute.