4.3 Strange Temp while running on muffs

[vince72801]

I have a 4.3 ser# 0m099909 with tks that was in salt and not flushed correctly. I posted this http://forums.iboats.com/mercruiser-i-o-inboard-engines-outdrives/should-i-replace-risers-manifold-4-3-a-590183.html

after the recommendations I received. I replaced the exhaust manifolds, risers, two flappers, thermostat (quick silver), plugs, wires, cap and rotor, and put a complete impeller kit.

I started her up today on muffs and idled about 800-1100 rpm, the temp gauge went up to 160 then just dropped to zero and then started slowly going back up to 160. This kept repeating, up to 160 the down to zero. My riser where getting a little hot to the touch, first left side the right, then left, then right. I plan on taking it out Monday for a load test but want to do everything I can prior to that. Also didn't seem to be putting allot of water out of prop, not sure if this was normal.

The only thing I didn't do according to the manual was instead of putting the gasket (pn 806871) between the thermostat and housing I used perfect seal. I put a new one with two metal rivet in but the other gasket wasn't shipped.

Is this normal operation or do I still have problems?


Gasket is item 3

 

[MarkSee]

Re: 4.3 Strange Temp while running on muffs

Also didn't seem to be putting allot of water out of prop, not sure if this was normal.
Is this normal operation or do I still have problems?

Not normal at all.

On muffs at 1100 rpm you should be seeing a continuous solid stream of water coming out the idle relief ports and a little out the prop.
What does the flow out of both idle relief ports look like and are they about the same?

Even on muffs the risers may get warm but should not get so hot that you should need to remove your hand.

Assuming the temp gauge is working properly the fluctuating up and down should not be happening either.

You'll need to wait for someone with more experience than me to help with the troubleshooting but I would not attempt to run it in the water under load until it is running properly on the muffs.

Mark

 

[Fun Times]

Re: 4.3 Strange Temp while running on muffs

The only thing I didn't do according to the manual was instead of putting the gasket (pn 806871) between the thermostat and housing I used perfect seal. I put a new one with two metal rivet in but the other gasket wasn't shipped.

Is this normal operation or do I still have problems?

If you did not install the cork gasket, then you will definitely have temp fluctuations just like what you're seeing. Common problem. Even if that gasket was damaged you would see temp fluctuation.

 

[dubs283]

Re: 4.3 Strange Temp while running on muffs

The only thing I didn't do according to the manual was instead of putting the gasket (pn 806871) between the thermostat and housing I used perfect seal. I put a new one with two metal rivet in but the other gasket wasn't shipped.

so you installed the gasket with the rivets and coated it with perfect seal??

you need the gasket with the rivets, this is so your temp sender and switch have a ground

you should not coat the gasket with perfect seal as this will cause an issue with the rivets continuity to gorund

my guess is once the engine comes to temp and the t-stat opens, the sudden rush of hot water past the gasket with the rivets causes a swelling and this coupled with the perfect seal causes a loss of ground thus the guage dropping then slowly rising once the gasket/housing cools

 

[vince72801]

Re: 4.3 Strange Temp while running on muffs

so you installed the gasket with the rivets and coated it with perfect seal??

you need the gasket with the rivets, this is so your temp sender and switch have a ground

you should not coat the gasket with perfect seal as this will cause an issue with the rivets continuity to gorund

my guess is once the engine comes to temp and the t-stat opens, the sudden rush of hot water past the gasket with the rivets causes a swelling and this coupled with the perfect seal causes a loss of ground thus the gauge dropping then slowly rising once the gasket/housing cools

This makes sense...but I didn't put it on the gasket with the rivets. I didn't have the cork gasket, which is on the other side of thermostat, so I used perfect seal instead. Item number 3

Thanks for the input!

 

[vince72801]

Re: 4.3 Strange Temp while running on muffs

If you did not install the cork gasket, then you will definitely have temp fluctuations just like what you're seeing. Common problem. Even if that gasket was damaged you would see temp fluctuation.

Thanks Fun Times, I don't understand this but I guess I be getting a cork gasket. This is a great board!

 

[tpenfield]

Re: 4.3 Strange Temp while running on muffs

I have a 4.3 ser# 0m099909 with tks that was in salt and not flushed correctly. I posted this http://forums.iboats.com/mercruiser...d-i-replace-risers-manifold-4-3-a-590183.html

after the recommendations I received. I replaced the exhaust manifolds, risers, two flappers, thermostat (quick silver), plugs, wires, cap and rotor, and put a complete impeller kit.

So, I take it that replacing all of these items had nothing to do with solving the problem? But at least you added some stimulus to the economy.

I always wondered what those little brass rivets were for in the thermostat housing gasket . . . but I figured it had to be something. As an alternative and a test, you could maybe hook a ground lead to a bolt on the thermostat housing :noidea:

 

[vince72801]

Re: 4.3 Strange Temp while running on muffs

Replaced gasket, solid 160 degree. Thanks everyone!

Now for the open water test.