Time for new thermostat housing?

[witchy woman]

You guys are usually on the money, so tell me - before I drop more money in the bucket - if I need a new thermostat housing. I have installed a rebuilt engine, chevy 350 to replace original 1999 chevy 305 (serial number 0L345352). Along with new block, I added new manifolds, risers and water pump. Engine is purring like new - but - the starboard side exhaust is hotter than port side. This engine has a 4-hose thermostat housing. The two outlets closest to the engine feed the exhaust manifolds. Of the two farthest from the engine, the port side is the supply and the large one on the starboard side feeds the water pump. At least that's what I've concluded by studying the flow diagrams. The large one feeding the water pump is hot. Shouldn't it be as cold as the supply side? The exhaust hose to the starboard side is hotter than the one to the port side which is almost as cool as the supply hose. Plenty of water coming out the exhaust on both sides of the engine.
So is my thermostat housing damaged or is this normal?

 

[alldodge]

I don't see an issue, both 5.0 and 5.7 used the same thermostat housing.
http://www.mercruiserparts.com/Show...r=2704&bnbr=130&bdesc=STANDARD+COOLING+SYSTEM

My 502 uses the same housing also. Your always going to have one side hotter then the other but it should not be so hot as you would get burned if you quickly touch it

 

[thumpar]

It is normal to have different temps from side to side. As long as it is not burning you it is fine. The water pump side will be as warm as the engine. The supply from the impeller will be the temp of the water you are running in.

 

[witchy woman]

All is not well. Ran the boat in the river over the weekend and still had overheating problems. Engine has a 140 degree thermostat installed. Idling, the engine temp reads about 150. At higher RPMs, with the boat on plane, the temp drops to about 125 but as soon as I pull back on the throttle, the temp climbs to 175 or higher. After the third repeat of this scenario, the engine overheated and the high temp cutoff killed it. Both sides of the exhaust were too hot to touch.

This is a new engine with new exhaust and water pump. I checked the thermostat in a pan of hot water and it opened and closed as it should. I have to think it is the pickup pump in the outdrive (Alpha) so I'll pull that and see what things look like. I did install a new impeller about a year ago, but maybe something is up with it.

Any other thoughts?

 

[alldodge]

You have a restriction somewhere or the pump in your drive is not working correctly. I would start by removing the hose from the transom plate going to the power steering cooler. Right at the transom plate there is a fitting which can and does get clogged up.

Edit: The sleeve and gaskets are in the housing correctly
http://www.mercruiserparts.com/Show...r=2697&bnbr=110&bdesc=Standard+Cooling+System

 

[Bondo]

I have to think it is the pickup pump in the outdrive (Alpha) so I'll pull that and see what things look like. I did install a new impeller about a year ago, but maybe something is up with it.

Ayuh,.... Welcome Aboard,.... The raw water pump impeller, 'n housin' is the 1st place to look in 'bout any overheat situation,....

 

[witchy woman]

You are right, AllDodge, something isn't working right. Not sure I'm physically able to get to that hose connection with the enging in the boat, so I backflushed it instead. I disconnected the hose at the thermostat housing and stuck the garden hose in it and opened it up. Water gushed through and out the outdrive (have gear housing off) and filled a 5 gallon bucket in about 15 seconds. So, I'm satisfied that water can get to the engine.

I'm a step ahead of Bondo. I pulled the water pump just to see what things look like and cant' find anything odd looking. No damage. Everything seems to be in order. So I'm sitting there, scratching my head and just fiddling with things and when I turn the propeller, the drive shaft rotates in a counter-clockwise direction as viewed from the top. Now I'm really confused because the manual shows it rotating clockwise. I can't rotate it clockwise. Again, this is an Alpha one, gen II. The diagram in the manual shows the fins of the impeller trailing in a counter-clockwise direction which is how I have it installed.

What's going on?

 

[alldodge]

If drive is in FWD then the prop must rotate counter-clockwise to rotate the drive shaft, this is because the clutch will not engage from the prop side any other way.

Question: Did you replace the engine circulating water pump? If so did you replace it with a clockwise rotating water pump?

 

[witchy woman]

I did replace the circulating pump. I looked up the part number on the mercruiser website with their parts catalog using the original engine serial number. When idling on the trailer, plenty of water is coming through the engine. At high rpms, the engine temp dropped drastically, then shot up again when I backed off the throttle. It appears as if the engine is getting too much water at high rpms and not enough at low rpms.

 

[alldodge]

I did replace the circulating pump. I looked up the part number on the mercruiser website with their parts catalog using the original engine serial number. When idling on the trailer, plenty of water is coming through the engine. At high rpms, the engine temp dropped drastically, then shot up again when I backed off the throttle. It appears as if the engine is getting too much water at high rpms and not enough at low rpms.

To me it acts like either the circulating water pump is not moving water or the thermostat is sticking. You do have a serpentine belt? Can you post a pic of the engine hose routing?

 

[witchy woman]

No Title

Posted a photo of the old engine. I used that photo as reference and just to be sure, I went out and double checked it before posting the photo. It seems to me as if water is bypassing the thermostat at high RPMs and then not at low RPMs. I don't know if that is possible or not with this housing. Are there supposed to be any check valves or bypasses built into it?

 

[alldodge]

If it's not to much trouble or if you would humor me, I would like the bottom large hose removed from the water pump on the left side facing the engine. Then take a light and look up in there and see which way the vanes are angled. If you still have the old pump, it could be compared to the new

 

[witchy woman]

Not humoring you, I'm testing your theories I still have the old pump, but when I look in the pipe, I can't see the vanes. They are not in line with the hole, they are "behind" it toward the engine. You mentioned earlier that you thought it sounded like a stuck thermostat and that's exactly what it seems like, except it would be sticking in both directions. If memory serves, it is not possible to put it in that housing upside down.

The only 3 parts that water flows through that I did not replace are the thermostat housing, the intake manifold and the PS cooler. The heads are new, the block is new and all the exhaust, including the hose fittings are new. I put a garden hose to the supply side of the thermostat housing and got water out the three pipes, most of it out the large one, less out of the two that feed the exhaust manifolds. The intake manifold and the therm. housing are both 16 years old and have been used in saltwater all that time.

If I have a blocked intake manifold, could enough water bypass the thermostat at high RPMs and "fool" the temp sensor into thinking things are cooler than they really are, then when the throttle is backed off, reality sets in and the high temp cut off sensor shuts down the engine? Is that a possibility?

 

[alldodge]

If I have a blocked intake manifold, could enough water bypass the thermostat at high RPMs and "fool" the temp sensor into thinking things are cooler than they really are, then when the throttle is backed off, reality sets in and the high temp cut off sensor shuts down the engine? Is that a possibility?

The high heat is probably shutting down the engine, but I don't think it's a stuck thermostat which opens up and closes again. Your not going to foo; an electro mechanical sensor (temp sensor). What I think is happening is the engine is pumping a lot of water but the cool water is not making it into the block. The water is keeping the thermostat closed because its passing by the thermostat. Once you slow down the water slows down and now the thermostat receives the hot water which is boiling. I still think its you circulating water pump, or your thermostat is in backwards.

Just my WAG