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Hot Manifolds

GAS engine, transmission and generator repair and maintenance discussion forum.
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390Express
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Hot Manifolds

Postby 390Express » August 7th, 2018, 12:04 pm

Risers are good, heat exchanger is good, exhaust manifolds on the port motor only are getting really hot, really fast. Where is the most common place to clog? At the water inlet port? At the joint between the riser and manifold itself? Any tips or tricks to getting it unclogged?

System is a full closed system, never in any salt water. No cracks in the manifolds.

**** Unrelated issue for extra credit... In the fiberglass exhaust T fitting or joint on the port motor, it sounds like there's debris in there. I really thought it was a spark knock (intermittent, sharp banging noise), but when I crawled down into the engine bay, it sounds like its coming from that exhaust fitting/joint/elbow. I can feel it with my hand and hear it much louder at the exh. fitting. Any idea what it could be, or how best to get it out, other than the obvious?

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Re: Hot Manifolds

Postby bud37 » August 7th, 2018, 5:22 pm

Not completely sure but there may be a flapper valve affair somewhere in there, forget what the official name is for it or the exact location. Have you had this section apart ?
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Re: Hot Manifolds

Postby mjk1040 » August 7th, 2018, 5:28 pm

Try running some RydLyme thru your engines to descale them. A 50/50 mixture for 4-6 hours in the engines will open any clogged scaled up areas and improve your fresh water cooling. There is a check/clapper valve in there that has a rubber edge on it and over time that rubber rots off and you have just metal and you here it flapping now.
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Topic author United States of America
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Re: Hot Manifolds

Postby 390Express » August 10th, 2018, 2:06 pm

mjk1040 wrote:Source of the post Try running some RydLyme thru your engines to descale them. A 50/50 mixture for 4-6 hours in the engines will open any clogged scaled up areas and improve your fresh water cooling. There is a check/clapper valve in there that has a rubber edge on it and over time that rubber rots off and you have just metal and you here it flapping now.


It's on the closed coolant side. I can just mix Rydlyme with the antifreeze? Or should I disconnect the manifold and try treating just the manifold?
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Re: Hot Manifolds

Postby buster53 » August 10th, 2018, 5:09 pm

If the manifolds are hot and it is a closed cooling system, shouldn't the engine block be the same temp as the manifolds? The same coolant is running thru the block and the manifolds so the temps of both should be the same or near to it.
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Re: Hot Manifolds

Postby 390Express » August 16th, 2018, 5:45 pm

Well... here was the issue... The block had little to no coolant in it. The reservoir was full, (I added a small amount at the beginning of the year, leading me to believe that the motor also full. It wasn't. Thankfully I only let it run for 10-15 minutes before realizing that the manifolds were unusually hot. I was trying to trace the issue by squeezing the hoses (to see which hoses didn't have pressure), and traced it back to the therm housing. Opened the term housing, and nothing... dumped in a gallon of antifreeze and half gallon of distilled water, and now everything is fine.

This is my first experience with a closed cooling system, and an expansion tank. Unlike a car, which primarily runs off of gravity (if you have low coolant in a car, and fill through the expansion tank, the coolant will go into the radiator), It seems that the marine counter-part runs off of pressure and a created siphon, so if you don't create the siphon buy forcing fluid into the tank, it won't run back out of the tank. That's my theory anyhow... Seems to be running fine now.

Idle on that motor is still very erratic, but one step at a time. It's getting there.
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Re: Hot Manifolds

Postby RobGunn » August 17th, 2018, 8:30 am

Just to eliminate possible options, I would replace the water pumps on the front of the engine and put a new thermostat in at the same time. Doing this may not help but its a inexpensive option to try.
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Re: Hot Manifolds

Postby bud37 » August 17th, 2018, 9:09 am

390Express wrote:Source of the post Well... here was the issue... The block had little to no coolant in it. The reservoir was full, (I added a small amount at the beginning of the year, leading me to believe that the motor also full. It wasn't. Thankfully I only let it run for 10-15 minutes before realizing that the manifolds were unusually hot. I was trying to trace the issue by squeezing the hoses (to see which hoses didn't have pressure), and traced it back to the therm housing. Opened the term housing, and nothing... dumped in a gallon of antifreeze and half gallon of distilled water, and now everything is fine.

This is my first experience with a closed cooling system, and an expansion tank. Unlike a car, which primarily runs off of gravity (if you have low coolant in a car, and fill through the expansion tank, the coolant will go into the radiator), It seems that the marine counter-part runs off of pressure and a created siphon, so if you don't create the siphon buy forcing fluid into the tank, it won't run back out of the tank. That's my theory anyhow... Seems to be running fine now.

Idle on that motor is still very erratic, but one step at a time. It's getting there.



Seems you may have to pressure test that side......I would want to know where all that coolant went, maybe contributing to the miss. When the coolant contracts on cooling it will pull the fluid from that tank, so long as there is coolant in there and no leaks in the system.
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Re: Hot Manifolds

Postby RobGunn » August 17th, 2018, 10:58 am

In a closed system, If your losing coolant and you are having a miss in the ignition, I would suspect a head gasket issue. Remove your oil fill cap and look at the bottom of the cap, is it clean or is it milky white? Milky white on the fill cap would indicate a large amount of moister in the oil, most likely coolant blowing past the head gasket.
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Re: Hot Manifolds

Postby 390Express » August 18th, 2018, 12:51 am

There’s no miss in the ignition. The only issue the motor is having is an erratic ide issue. It rpms fine, and sounds great. Seems like the IAC is bad. I believe the coolant was intentionally drained by whomever winterized the motors. There’s no coolant in the oil, no smoke in the exh.

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