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View Full Version : LT1 Exhaust Manifolds different Temperatures


Bruce Jones
07-17-2010, 04:16 PM
I noticed today after running up my 1998 ProStar 190 after being stored for the winter that the top side of the passenger side exhaust manifold is running noticeably hotter than the driver side. The hose that comes off the passenger exhaust manifold also vibrates much more than the other as if the engine were running rougher on that side. The water exiting at the rear of the boat appears to have the same volume however the passenger side water is noticeably hotter. Where the water is entering the manifold at the front is the same temperature on both sides. In summary it is as if the passenger side of the engine is running hotter than the driver side.

I have pulled off all the water hoses and dug around with a wire to ensure there is are no blockages. I pulled the spark plugs and they look normal and the same.

Any thoughts as to what might be the problem?

Thanks,
Bruce

captain planet
07-27-2010, 02:08 PM
I have the same boat but have never had that problem. Does the engine idle smooth?

JLeuck64
07-27-2010, 02:14 PM
I have tried to keep up with all threads relating to the LT-1 engine and from what I recall it is normal for one side of the engine to run hotter than the other side. Not abnormal just a characteristic of the cooling system design...

captain planet
07-27-2010, 02:27 PM
I have tried to keep up with all threads relating to the LT-1 engine and from what I recall it is normal for one side of the engine to run hotter than the other side. Not abnormal just a characteristic of the cooling system design...

Really? I haven't noticed. I'll have to check mine this weekend.

How is your boat running?

Bruce Jones
07-27-2010, 03:56 PM
I ended up taking the riser off the manifold on the passenger side, stuck a rag into the manifold where the exhaust gases exit and then flushed water through the front of the manifold with a garden hose. There was a small bit of crud visible at the front of the manifold however did not see anything of substance come out anywhere else. After reassembly and running the motor up to operating temp the passenger riser is now running ever so slightly cooler than the other side so I can only assume there was some sort of blockage.

The engine itself looks to be running smoothly and at the exhaust sounds normal although the hose off the rear end of the passenger side manifold still vibrates more than the other. I have not had time to check this out so any thoughts are appreciated.

JLeuck64
07-27-2010, 04:41 PM
Really? I haven't noticed. I'll have to check mine this weekend.

How is your boat running?

Well ya know... there is a TON of stuff up here on this forum and I just remembered reading a comment about the temp difference once upon a time. Our hands make terrible temp gauges... and in my own un-scientific experiment all i can say is a package of Ball Park Franks cooks faster on one valve cover versus the other! LMAO!!!

gotta_ski
12-17-2010, 09:47 AM
I too have the LT-1 in a 98 190. I have a theory on why the two manifold risers are a different temp. I noticed this one day after driving the boat in November in eastern WA. I guess the air temp was around 45 and the water between 35 and 45 degrees.

Each manifold riser has a small line running to it. The starboard side's line (at least on mine) comes from the head bleeder line, while the port side comes from the bubble catcher on the water going to the upper thermostat.

I think the port side line is getting much colder water than the starboard side, causing the difference in riser temperatures. This is just my theory, and I'm very new to this motor, so I could be totally wrong. Can anyone chime in to say yes or no to this? I'd like to know.

I'm in the process right now of moving the head bleeder line from the back of the engine to the front as shown in gibbons post. From what I read this should have been done at the factory, but for whatever reason it wasn't. I think the line being at the back and not immediately taking out any air in the heads is what causes some owners to experience erratic and high engine temperatures when the boat is first put in the water for the season or after trailering. I'd also like to hear other's thoughts on this as well. It seems pretty straight forward to me, but I could be missing something. Please post if you know or think anything different.

blackcreek
12-18-2010, 11:08 AM
Same thing on mine.http://mastercraft.com/teamtalk/showthread.php?t=33959&highlight=lt-1

The bleed line from the heads dumps into the right side riser on mine also. That hose bleeds the hot water from both heads to the riser. At low water flow the riser will heat up to almost head temp. The other side hose bleeds the water from the cold water loop before the thermostat and dumps it in the other riser so it stays cool. At high rpm when there is lots of water flushing through the manifolds the small amount of bleed from the small hoses is not enough to make a difference. Do a fast run for a few minutes then stop and check each riser for similar temp, mine were the same. Once you idle for any length of time the riser temp will start to split.