4.3 mercruiser temp issues

[PuddleJumper]

I have twin mercruiser 4.3 TBI 2000yr B3 drives. As part of my summerizing process I put in new t'stats in both engines. They are 160 deg. The starboard eng warms up to about 170-175 on guage. The port engine runs up to 190+ then drops to 160 in a constant repeating cycle. Occurs over 1-2 minute cyles. This is at 3500 rpm. At 1500 rpm it is much less pronounced (179-180) I notice that the sbd riser on the port eng is MUCH hotter to touch than the port side. Also much hotter that the corresponding riser on the sdb eng.
Both raw h20 pumps rebuilt last year. Bad t'stat? Any thoughts?

 

[pillsy]

Re: 4.3 mercruiser temp issues

Just read another post that said the guy tested the thermostat buy putting it in water and heating it on the stove top to see if it opens at the correct temp. Had the same thing happen on a car and it was the thermostat. Sound like the cheapest thing to check. Good luck! You may also take the the thermostats out and run it for a while to see if the problem is better or worse.

 

[PuddleJumper]

Re: 4.3 mercruiser temp issues

I'm not sure the boiling test will tell me as I'm pretty sure the tstat is opening.It acts like it's either open or closed with no in between. I'll probably pick up another tstat to try. Just wondered what the symptoms sounded like to those with more experience.

 

[cr2k]

Re: 4.3 mercruiser temp issues

You may have a plugged riser, or manifold.

 

[PuddleJumper]

Re: 4.3 mercruiser temp issues

Would a partially plugged riser on one side cause the temp swings I'm seeing?

 

[PuddleJumper]

Re: 4.3 mercruiser temp issues

I guess I'll start with the easiest/cheapest steps first. When I get back to the boat 1)change t'stat, if not fixed then 2) service sea water pump then 3) Pull manifold/riser and inspect.
Am I missing anything?

 

[cr2k]

Re: 4.3 mercruiser temp issues

I have seen temp gauges swing for no reasons. Mine does and we spend hours trying to make one quit. New wires, new gauge new sender and still swing.

Get an IR temp reader and see what is really going on. Marine temp gauges are notoriously poor and you could be chasing nothing.