1994 7.4L Bravo Gen V temperature

[JGabeH]

I will test the water pump. Make sure it's pumping as it should. I changed the impeller last May but it definitely could go bad over a winter of sitting. Is there a chance that the rv antifreeze gelled due to the engine being in salt water before? The exhaust manifolds and risers are probably at the end of their life and could be the cause. Is there a way to test those without disassembly and inspection?

 

[alldodge]

I don't know of a way to test the exhaust without removal. Once removed, open and visual inspect, then if they look good enough, use acetone in them to check for leaks.

Don't see the rv antifreeze gelling in one season

 

[JGabeH]

How do I test the manifolds for leaks with acetone?

 

[alldodge]

Pour acetone in the water jacket and slowly move it around to see if it leaks out. Acetone will leak out where water will not

 

[HT32BSX115]

There is another way to test manifolds, that's a tad time consuming but is reliable.

I had one of mine off last year (that I suspected leaking) ........I made a block-off "plate" using an old regular block-off gasket (used for full closed cooling systems) which is literally a thin piece of stainless steel sheet.

Then, I placed that plate "sandwiched" between two pieces of regular gasket material with gasket sealant and bolted (torqued to "spec") it to the manifold using the riser, effectively sealing the water jacket in the manifold.

I then pressured it up to about 20 psi (with a gage connected) and closed it off using a ball-valve. There was the chance that my gasket lashup wouldn't hold the pressure but it did hold 20PSI all day. :thumb:

The BEST pressure test of course, IS a pressure test!

Cheers.

Rick

 

[JGabeH]

I finally got my boat home to look at the oveheating issue. I don't think the manifolds are leaking but am concerned they may be corroded and plugged. First I will test the water pump. Then themostat. Then I will disassemble manifolds if needed.

 

[JGabeH]

So when I tested the boat and it overheated I left the batteries on and they drained. Currently charging to see if they will hold before I can cheek the water flow of the water pump. I did notice that my exhaust risers are stainless steel. Does this mean I can rule out that they are not allowing water through?

 

[alldodge]

So when I tested the boat and it overheated I left the batteries on and they drained. Currently charging to see if they will hold before I can cheek the water flow of the water pump. I did notice that my exhaust risers are stainless steel. Does this mean I can rule out that they are not allowing water through?

Sooner or later they all rust through, just the matter of how long it takes. Fresh may be a life time, salt not so much, that said, never take anything for grated

 

[JGabeH]

Looking at exhaust manifolds now. Which brands are trusted? OEM is always good. What about GLM or H2O?. Gonna change my exhaust flappers while I'm in there.

 

[HT32BSX115]

There are more than a few members here that have had GLM and possibly others leak because the sealing surfaces weren't flat and "true" so if you get anything other than OEM or maybe BARR, be sure to do a flatness check of the riser sealing surface.

A couple of people with access to a milling machine were able to make the "bad" ones good by "taking a little off the top"!!

Not suggesting you'll get bad after market manifolds....people install them all the time with no problems......., just saying to be sure to check before you assemble.

 

[Bondo]

A couple of people with access to a milling machine were able to make the "bad" ones good by "taking a little off the top"!!

Ayuh,.... Which is Why I suggest usin' a flat file to check flatness of both the manifolds, 'n risers,....

I flattened my GLMs with a belt sander, granted a huge machine shop belt sander, but a belt sander none the less,...

 

[JGabeH]

I've been working in the boat today. It seems the water pump may not be pumping water. I disconnected the water line going into the thermostat housing and nothing comes out when I start the engine. The impeller looks fine. The pump seems to be spinning. Water flows through both hoses from and to the pump fine when I manually pour it in. I don't think there is any way that I reversed the hoses as they are routed and are difficult to connect the wrong way. Can anyone confirm on a 1994 Mercruiser 7.4l Bravo 1 that the intake hose is on top of the pump and outlet is the bottom hose? The exploded diagram in the manually kind of pictures it the other but I think its just the drawing.

 

[alldodge]

Can anyone confirm on a 1994 Mercruiser 7.4l Bravo 1 that the intake hose is on top of the pump and outlet is the bottom hose?

That is backwards, intake on the bottom................ unless someone rotated the pump and drilled new holes to mount it

 

[JGabeH]

Thats good news and bad news I guess. Good news it may be an easy fix. Bad news I'm an idiot. I thought I had everything in place and the motor mount gets in the way of the its hose on the bottom. Also saw in a youtube video someone removing a pump with inake on top. My mistake. Thanks for all the advice so far.

 

[alldodge]

It does happen to others so your not alone. Look at the back of the pump, it identifies LH and RH rotation outlets, yours would be LH

 

[JGabeH]

No Title

Does this seem correct? I agree that mine is a LH rotation but my pump shows the LH OUT on the bottom when installed. (See pic) I started the engine with the intake on bottom and outlet hose on top and no water came out the hose that connects to the thermostat after 10-15 seconds of idling. My impeller looks good and feels flexible. Is there any way the pump pulley is spinning but not the output shaft?

 

[bman440440]

Does this seem correct? I agree that mine is a LH rotation but my pump shows the LH OUT on the bottom when installed. (See pic) I started the engine with the intake on bottom and outlet hose on top and no water came out the hose that connects to the thermostat after 10-15 seconds of idling. My impeller looks good and feels flexible. Is there any way the pump pulley is spinning but not the output shaft?

LH out means that you connect the hose that goes TO the thermostat housing to it (LH out)... and the hose from your drive/water pickup to the other

 

[JGabeH]

Correct. So based on my configuration the hose from my water pump TO my thermostat should be on the bottom. Right? Alldodge had said that my intake is on the bottom, not my out. I just want to be sure it is hooked up right. Either way, it doesn't seem to be pumping. How long should it take running before water is at the thermostat?

 

[bman440440]

Correct. So based on my configuration the hose from my water pump TO my thermostat should be on the bottom. Right? Alldodge had said that my intake is on the bottom, not my out. I just want to be sure it is hooked up right. Either way, it doesn't seem to be pumping. How long should it take running before water is at the thermostat?

yes based on your setup from water pump to your thermostat housing goes to the bottom connection... you say either way it doesn't seem to be pumping... meaning that you have had the water intake hose connected to the top and the out to the bottom and still no water pumping?

 

[JGabeH]

Yes. I've connected to the top and bottom and still no water coming out the line at the thermostat. Water seems to flow freely through both the thermostat hose AND the intake hose from the drive. How long should it have to run on the hose before I see water?