5.7L Engine Riser Temps

Hello All,

I recently picked up a used boat and overall it seems pretty solid. It's a 1998 Stingray with 5.7L Mercruiser with an Alpha One outdrive. While doing the inspection, I had a mechanic come down and give everything the once over. He gave the boat a solid thumbs up but did point out that the starboard riser was running hot while the port was cool. He suggested there was likely some blockage somewhere as they should both be cool to the touch where the starboard was pretty warm (you could only touch it for about 5-10 seconds).

I then went to a boat shop to buy new impeller, etc. (boat had been sitting for a couple of years) and the mechanic there said it was normal for the boat to run warmer on one side.

The boat seems to run about 160 according to the gauge but I need to check the gauge to make sure it is working because I never saw it hit any other temp, even after sitting for a while.

In any case, should both risers be running about the same temp and be cool to the touch (not cold, just not hot).

Thoughts?

Regards,
Java

Re: 5.7L Engine Riser Temps

Java Jack said:

Hello All,

I recently picked up a used boat and overall it seems pretty solid. It's a 1998 Stingray with 5.7L Mercruiser with an Alpha One outdrive. While doing the inspection, I had a mechanic come down and give everything the once over. He gave the boat a solid thumbs up but did point out that the starboard riser was running hot while the port was cool. He suggested there was likely some blockage somewhere as they should both be cool to the touch where the starboard was pretty warm (you could only touch it for about 5-10 seconds).

I then went to a boat shop to buy new impeller, etc. (boat had been sitting for a couple of years) and the mechanic there said it was normal for the boat to run warmer on one side.

The boat seems to run about 160 according to the gauge but I need to check the gauge to make sure it is working because I never saw it hit any other temp, even after sitting for a while.

In any case, should both risers be running about the same temp and be cool to the touch (not cold, just not hot).

Thoughts?

Regards,
Java

Click to expand...

Ayuh,.... Welcome Aboard,... He's Right,... They're Never the Same,...

Re: 5.7L Engine Riser Temps

Hi. From reading other forums/posts I believe it is normal for one riser to be warmer than the other - BUT they should not be too hot. It sounds like mechanic #1 was right. You have signs that all is not well with that riser. May be time to check/replace them.

Re: 5.7L Engine Riser Temps

Thanks for the replies.

While the boat is a 1998, it only has 134 hours on the motor and has been sitting for a couple of years but was winterized before being stored.

I will try pulling off the riser tomorrow and seeing if there is any blockage. I am assuming that they should both be able to be touched for a length of time when boat is running, correct and not so hot you feel the need to remove your hand after 10 seconds?

Re: 5.7L Engine Riser Temps

Java Jack said:

Thanks for the replies.

While the boat is a 1998, it only has 134 hours on the motor and has been sitting for a couple of years but was winterized before being stored.

I will try pulling off the riser tomorrow and seeing if there is any blockage. I am assuming that they should both be able to be touched for a length of time when boat is running, correct and not so hot you feel the need to remove your hand after 10 seconds?

Click to expand...

Although it is low hours the risers have been living in a wet environment for 15 years and the winterization process would only be beneficial if the cooling system had been flushed with antifreeze. ( many folk say this isn't necessary - but that's a separate topic )
In my mind the advice of mechanic 1 should be followed, as he actually felt the riser. Mechanic 2 didn't have that opportunity.
Best to check it out and yes, it should run cool enough to pass the touch test.

Re: 5.7L Engine Riser Temps

Thanks. I'll be giving a look over tomorrow. Figure I will check out the thermostat housing at the same time. Then do the impeller as well.

Re: 5.7L Engine Riser Temps

Welcome to the forum.
This cooling difference is a known thing with the V6 and V8 Mercruisers. If you pull the risers you will probably find them OK. Make sure to put in new gaskets if you do.
To get the riser to cool a bit just pick up the RPMs in the water. Muffs are not a true test. If you get a laser thermometer you will find they are probably 30 or 40 degrees apart at worst.
Oh, also. NEVER start the motor unless there is water to the drive. Don't run the motor with the drive tilted any higher than the trim stop.
HAVE FUN!