Exhaust manifold swap

[jaybrassmonkey]

So I replaced my engine with a reman last year. It runs great but was running hot with the thermostat in place. Out of frustration I ran it without the thermostat. It ran up to temperature and I kept an eye on the condition of the oil for gunning up and such, no issues there. To recap, I've checked for obstructions, hoses are good, impeller has been changed, getting good flow. The only thing I can think of is that my previous motor had the bat wing style exhaust manifolds. I had to switch to the 2 piece model with the new engine. I did keep the old thermostat housing, the single T version. Do i need to switch the Thai housing to the double T version with the switch to the 2 piece manifolds?

 

[Scott Danforth]

You're on borrowed time with the batwing manifolds

 

[alldodge]

What engine are you discussing, size and year helps.

 

[jaybrassmonkey]

Sorry, it's a 97 4.3 mercruiser (Chevrolet). I no longer have the batwing manifolds, switched to the two piece with the engine swap.

 

[alldodge]

If you have the thermostat housing below your good

What do you mean you have a single T housing?

 

[jaybrassmonkey]

Yes, that's the one I have. I've seen another one where there are 2 other hoses that go to the manifolds, kinda double stacked of the small hoses. I just can't figure out why I run hot with the thermostat installed.

 

[alldodge]

First you do want the thermostat installed, this keeps the block full of water

Have you checked the power steering cooler to see if it is clogged or has pieces of the impeller in it?

Do you have an Alpha or Bravo drive? the drive type should make no difference on cooling, just need it for thought

The stack type use check valves in the housing to help keep the block full. The stack housing does not work near as well as the current one your have.

 

[jaybrassmonkey]

Geeze, idk what it can be then. I've checked the ps cooler, the ypipe is not obstructed, good flow into the housing, new manifolds, new gaskets in the manifolds, new impeller and gasket kit, water intake hose is clear. It is an alpha 1 gen+ outdrive. I'll be pulling it apart shortly to fix the gear oil hose (leaking) and will probably check the impeller again and replace the gaskets.

 

[alldodge]

Only other thing if all checks out would be the circulating water pump. Some have had the impeller blades break loose, but this is rare

 

[jaybrassmonkey]

Checked that too! Lol

 

[fieromx3]

temp. gauge reading incorrectly? coolant temp sensor faulty?

 

[jaybrassmonkey]

No I'm pretty sure the gauge is correct. I changed the temp sender too. It does run hot to the touch in the manifolds and the engine itself.

 

[alldodge]

No I'm pretty sure the gauge is correct. I changed the temp sender too. It does run hot to the touch in the manifolds and the engine itself.

Not hot to the touch?

 

[jaybrassmonkey]

Yes, the manifolds and engine is hot to the touch. It actually did overheat one time while trying to figure out what was going on. I must have gotten lucky because there aren't any performance issues.

 

[alldodge]

Another thing that could cause your issue is the transom assembly water feed thru. Over time the hose deforms and/or can get clogged up which will restrict flow. If you can get at it I would remove the fitting (item 17) and see what it looks like.

http://www.mercruiserparts.com/Show...50.png&inbr=1942&bnbr=70&bdesc=GIMBAL+HOUSING

 

[Bondo]

Yes, that's the one I have. I've seen another one where there are 2 other hoses that go to the manifolds, kinda double stacked of the small hoses. I just can't figure out why I run hot with the thermostat installed.

Ayuh,.... Where do you have the hoses hooked to the new manifolds,..??

 

[jaybrassmonkey]

I have checked the inlet hose through the transom and it is clear.

The hoses are connected to the bottom of the exhaust manifolds.

 

[alldodge]

Did you check on the inside? Here is one which looked fine until the hose fitting was removed

 

[jaybrassmonkey]

I ran a hose to it and it flowed free and clear from both sides

 

[alldodge]

Running on a hose it will flow clear on both sides even if the transom inlet is partly clogged. To overheat at higher rpms your either not getting enough water due to a restriction coming in or keeping water from going back out, or the water is not circulating correctly