Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

[Maraian]

98 5.0L merc ( sn 0L093162) raw water cooled, just replaced exhaust manifolds and risers ( because of milky oil, resolved).

Now at wot, runs hot close to 200, and starboard riser is hot to touch.

Is it common for the Y shaped exhaust tube (that connects risers to outdrive) to become clogged and cause unilateral overheating?

Boat is an 1983, outdrive is volvo 280!

Or is it likely that the starboard manifold/ riser was not installed correctly?

 

[Maraian]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

Also, replaced thermostat last year.

 

[ktbarrentine]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

Looks like this one needs to get moved to the Volvo forum. Check the impeller?

 

[Don S]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

When was the last time you replaced the impeller?

 

[Maraian]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

Impeller is new. Pumps water. Engine operates at normal temps up until about 3500 rpm for extended periods of time.

 

[Maraian]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

The unilateral riser overheating is very suspicious to me?

 

[Don S]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

The unilateral riser overheating is very suspicious to me?

Me too. What's a "unilateral riser"

 

[Maraian]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

Me too. What's a "unilateral riser"

By unilateral riser, I mean just one side, the starboard exhaust manifold riser is much hotter than the port riser.

 

[Maraian]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

Update: Pulled the new hot riser to inspect Y exhaust tube and one of the two main water channels is partially blocked!

 

[Maraian]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

Update: Pulled the new hot riser to inspect Y exhaust tube and one of the two main water channels is partially blocked!

I meant one of the two main water channels on the Riser!

 

[djmakko]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

Update: Pulled the new hot riser to inspect Y exhaust tube and one of the two main water channels is partially blocked!

How is it blocked?

 

[Maraian]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

 

[Maraian]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

 

[04fxdwgi]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

Which gaskets did you use between the manifolds and risers? How were they positioned" Are the manifolds Volvo or Merc configurations?

What else of Volvo name was used on the Merc engine swap? Was other stuff like Volvo themostat housing swapped?. The basic engine doesn't care what it's attached to, but I would keep cooling / exhaust parts family consistant, using all Merc or all Volvo stuff. Not Volvo manifolds w/ Merc stat housing and hose routing and visa versa.

The "Y" pipe should be fine, as it's just a pipe that flows the exhaust. On Mercruisers, exhaust shutters falling apart winding up down inside is another story, but your "Y" pipe is a Volvo part, if you are using a Volvo drive.

PS: Those riser passages look to be OK and I see no restrictions there.

 

[Maraian]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

Thanks for the advice. I used the restrictor gaskets that came with the aftermarket riser elbow! I now see ( thanks to this site, Don S.) a service bulletin stating to use full flow gaskets, hopefully that will resolve the high RPM overheating.

As for the riser obstruction, I sent those pics to the manufacturer ( Barr) they said they looked obstructed and supplied me with a new one. However, when I recieved it looked almost identical and I'm still overheating.

I believe everything (thermo housing, ect )is mercruiser on the motor, but not completely sure. I replaced the exhaust manifolds with the Merc ceramic coating, but went with the Barr elbows, in part ,due to local availability ( they were in stock at my local parts store, the merc elbows were not, and cost, of coarse)

I running about 200 degrees at 4500 RPM, when i back off the throttle the temp will falll back into normal range ( 150-170). It seems to me that this could be attributed to the restricted gaskets, well see this afternoon.

Thanks again for the info on the volvo Y tube not having the flapps, i spent 30 mins trying to fish them out.

 

[Maraian]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

Well, changed the gasket to full flow, but still running hot at wot. Seems to be running a little cooler, but still hot, probably 185-190 degrees, quess I'll look for a inflow restriction and replace the thermostat. Checked the power steering fluid cooler, and external inflow grates on the drive.
Any suggestions much appreciated.

 

[04fxdwgi]

Re: Replaced exhaust, now overheat at wot, clogged Y exhaust tube?

Well, changed the gasket to full flow, but still running hot at wot. Seems to be running a little cooler, but still hot, probably 185-190 degrees, quess I'll look for a inflow restriction and replace the thermostat. Checked the power steering fluid cooler, and external inflow grates on the drive.
Any suggestions much appreciated.

Barring any design flaws when mixing systems, I would guess there is a blockage somewhere in the raw water system (starting at the outdrive and working towards the pump) / weak raw water pump / blockage in one of the oil / PS coolers (if you have them) causing insufficient flow. And I keep levitating towards the raw water pump / feed going to it.

Also, if you have even the tiniest air leak before the raw water pump, it'll suck air along with water, aerating the raw water and reducing your cooling capacity.