Mercruiser 5.0 MPI no longer running as warm

[FliesAndFloats]

2005 Maxum 2400 SD w/ Mercruiser 5.0 MPI Alpha I Gen 2.

When I purchased the boat last year the boat would warm up and the temperature gauge would run straight up and down between 170 and 180. Now, assuming the gauge is accurate, the boat appears to take much longer to warm up and only seems to hit around the 25% mark on the gauge at around 140 degrees. My thought is that I had it in the saltwater for several days at the end of the Grouper season and that maybe something got wedged in the thermostat. I want to make sure my theory sounds...umm...sound before I just go and replace the thermostat. Also, is there a recommended thermostat for this engine? I've read that mercruisers in saltwater use 140 degree thermostats to increase flow through the manifolds to help prevent buildup, but the gauge seems to indicate that something a little warmer looks "correct."

 

[alldodge]

2005 Maxum 2400 SD w/ Mercruiser 5.0 MPI Alpha I Gen 2.

When I purchased the boat last year the boat would warm up and the temperature gauge would run straight up and down between 170 and 180. Now, assuming the gauge is accurate, the boat appears to take much longer to warm up and only seems to hit around the 25% mark on the gauge at around 140 degrees. My thought is that I had it in the saltwater for several days at the end of the Grouper season and that maybe something got wedged in the thermostat. I want to make sure my theory sounds...umm...sound before I just go and replace the thermostat. Also, is there a recommended thermostat for this engine? I've read that mercruisers in saltwater use 140 degree thermostats to increase flow through the manifolds to help prevent buildup, but the gauge seems to indicate that something a little warmer looks "correct."

What is your engine serial number?

 

[Fun Times]

The thermostat is typically the first place to inspect when you have a sea water cooled marine-engine not getting up to the correct temperature. Debris will usually hold the thermostat open in-turn not allowing the engine to warm up to the recommended temp.

Being that you mentioned you have an MPI engine, it's best that you stay with recommended thermostat (160*) to keep the programmed fuel/timing curves relatively close to what the engine manufacturers set your engine (ECM) up to run at.

 

[Scott Danforth]

2005 Maxum 2400 SD w/ Mercruiser 5.0 MPI Alpha I Gen 2.

When I purchased the boat last year the boat would warm up and the temperature gauge would run straight up and down between 170 and 180. Now, assuming the gauge is accurate, the boat appears to take much longer to warm up and only seems to hit around the 25% mark on the gauge at around 140 degrees. My thought is that I had it in the saltwater for several days at the end of the Grouper season and that maybe something got wedged in the thermostat. I want to make sure my theory sounds...umm...sound before I just go and replace the thermostat. Also, is there a recommended thermostat for this engine? I've read that mercruisers in saltwater use 140 degree thermostats to increase flow through the manifolds to help prevent buildup, but the gauge seems to indicate that something a little warmer looks "correct."

flow rate thru the manifolds is the same regardless if you have a 100 degree or a 1 million degree thermostat.

pull your thermostat, and replace it with the correct one for your MPI motor. it will either be a 160 or a 180 depending on your motors EFI tune.

 

[HT32BSX115]

2005 Maxum 2400 SD w/ Mercruiser 5.0 MPI Alpha I Gen 2.

Now, assuming the gauge is accurate, the boat appears to take much longer to warm up and only seems to hit around the 25% mark on the gauge at around 140 degrees.

Before you pull everything apart and replace parts, you might consider using an inexpensive IR temp gage like the following $20 one from HF to verify your temp gage.

Just point it at the T-stat housing!