GT40 Port side riser hotter than starboard side

[74corvette]

I have a 2001 SAN with the GT40. Last summer I noticed the port side riser is considerably hotter than the starboard side. I replaced the exhaust manifold and riser gaskets and it is still hotter. I also have a dripless packing on my boat hooked up to the port side. Should I move the dripless packing to the starboard side? Thanks for the help

[JP75]

Plus 1

I have a 2002 196 with GT40 and noticed the exact thing this past weekend. Skied for about 45 minutes and blue smoke started coming from exhaust. Shut it down. Port side riser was hot. Had mechanic here to look at it; noticed it was about 1/2 quart high on oil, pumped some out... Idled it for some time today and the port side was still considerably hotter than starboard riser. Impeller seems fine. Any suggestions?

[74corvette]

I'm going to borrow a temp gun to check it again in the next couple of days to see what the actually temp difference is between the two.

[JayG80]

My boat's right exhaust riser was hotter and I could never determine the source. I just lived with it after no cure from a new thermostat, impeller and riser gaskets,

Later during that ski season the boat suffered a loss of hole shot that required action.

Both issues were difficult to diagnose even after throwing new parts at it. LP Fuel Pump, new filter and hose to HP pump.

Determined the muffler was bad. Once I replaced the muffler, the heat and performance issues were cured.

May not be your issue but something to inspect. Besides the heat and performance issues; My signs were: a change in exhaust sound from bad internal muffler baffle, warm bilge water from a pinhole leak, muffler would pillow up and back to normal when the boat was started.

[DaveNH]

Oil level has nothing to do with a riser being hotter than the other. Neither does fuel system issues. You need to look at cooling water flow. Have you changed the impeller this season? If not, do so now and then run the boat on the trailer, either run with an open T to a water hose or out of a bucket, not with a pressurized hose directly into the raw water pickup. See if adequate water is running out the exhaust. Then, pull the riser drain plug and see how much rust and crap comes out, clean it and flush it out as best you can. You want to prove out that you have enough cooling water flow to the riser and no passages are blocked.

[wakejunky]

I had the same problem. A few years back I blew an impeller and things ran fine for at least a year. Then one day the port side riser got extremely hot. I figured it was the water going to the riser was somehow being restricted. Diagnosed it to the thermostat housing and found that there is a water inlet hole from the thermostat to the risers had finally gotten plugged by an impeller piece. Replaced the thermostat while I was at it and gaskets and been good ever since.

[Fgroce]

I found the same thing in my thermostat housing, riser water hole plugged with impeller parts.

[74corvette]

I took off the thermostat housing and didn't see any obstructions. Rerouted the dripless packing pickup. Just trying to find a new thermostat to put it back together


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[JP75]

Oil level has nothing to do with a riser being hotter than the other. Neither does fuel system issues. You need to look at cooling water flow. Have you changed the impeller this season? If not, do so now and then run the boat on the trailer, either run with an open T to a water hose or out of a bucket, not with a pressurized hose directly into the raw water pickup. See if adequate water is running out the exhaust. Then, pull the riser drain plug and see how much rust and crap comes out, clean it and flush it out as best you can. You want to prove out that you have enough cooling water flow to the riser and no passages are blocked.

Thank you. for this. We have checked the impeller; looks good. Will be putting a new one in before firing back up. We also checked the thermostat. From what we can tell, looks good; no impeller parts or anything blocking. Again, planning to put a new one in before firing back up. We also removed the exhaust hoses. Both hoses on each end of the fiberglass tube were blistered inside from the heat last week. We removed the risers, they look pretty clear and not rusty. Blew air through the hose that goes from the thermostat to the port manifold and does not seem blocked. Where do we go next?

[2000superdare]

Maybe open the drain plug while you run it and see how much if any water is flowing through it. Also make sure that the hose connect cap is on, could cause air to get in system. I can always tell when mine is open engine will run hot. If its hot it has to be water flow!

[Tjca77]

What is your engine temp? While running can you place your hand on the port riser? Both should be warm, but not so hot you cannot touch them.

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[74corvette]

The engine temp is at 160 consistently and I can put my hand on the port side riser but it is a lot hotter than the starboard side. I am hoping that it was just because I had the pickup for the dripless packing right before the port side manifold. I relocated the pickup to a different spot so hopefully that helps. My new thermostat and gasket should be here Monday so I can test it out. Skidim also stated that one side always runs hotter than the other side so hopefully that is the case and I'm just being cautious.

[74corvette]

Installed the new thermostat and relocated the pickup for the dripless packing and ran it in the driveway. Everything is now good, starboard riser was around 88 degrees and port side at 90 degrees with engine up to temp at 160. Thanks again for all the help. Now all I have to do is get time to get it back on the water.