Puffing sound from rear of engine

[karayj]

In my previous post I had mentioned that I replaced the head gasket on my boat and I will guarantee that this has something to do with it and it may have had something to do with my boat not starting after running it for about 2 hours vapor lock. Now I really haven't had them desktop too needed to test that but I will today but recently after running it for about 20 minutes stopping and then starting it back up after 15 or 20 minutes she starts right up which is good.

what I've been noticing and not mentioning in previous posts about carburetor issues such as linkage I've noticed that there's a puffing sound coming from the rear of the engine which could have been causing the vapor lock I'm not sure. I'm trying to figure out where this popping sound could come from I mean realistically it's either intake or exhaust in most cases but this being a boat I could be wrong. Yesterday I noticed 2 bolts on the intake needed to be tightened up a little bit more they were snug but not torqued I'm wondering if that is where the puffing sound was coming from I will test it today.

I also noticed in the back of the engine on the first time start up I could smell and see some steam obviously from antifreeze burning off, my fear which I could be completely wrong is a head gasket issue but would I really hear a puffing sound from a head gasket? Wouldn't it be leaking any freeze all the time I did do a pressure test I mean it came down a little bit after 5 minutes but not much. So there's a combination of three things puffing sound and after three weeks about 3 cups of antifreeze missing when it's “COLD” after warm up it comes up a bit but not much.

 

[achris]

engine? year? model? serial number?

 

[Scott Danforth]

I also noticed in the back of the engine on the first time start up I could smell and see some steam obviously from antifreeze burning off, my fear which I could be completely wrong is a head gasket issue but would I really hear a puffing sound from a head gasket? Wouldn't it be leaking any freeze all the time I did do a pressure test I mean it came down a little bit after 5 minutes but not much. So there's a combination of three things puffing sound and after three weeks about 3 cups of antifreeze missing when it's “COLD” after warm up it comes up a bit but not much.

you dong have vapor lock. hydro lock maybe

if you loose antifreeze, you have something wrong. PERIOD

my guess is AF is leaking into the cylinder

when you do a pressure test, you need to have a completely empty cooling system. any drop in pressure is bad. it should hold 15 psi forever.

so, what motor is this?

 

[Bondo]

Ayuh,..... An intake leak won't huff, nor puff, it just sucks,.....

An exhaust leak will huff, 'n puff,.....
To find an exhaust leak, start the motor, 'n run yer hand all 'round all the exhaust gasket areas,....
When yer hand gets burnt, ya found the leak,.....

 

[karayj]

I am so sorry forgot to mention the engine 89 3.7 merc 2bbl

I did do the hand check for the exhaust leak and I was not able to find much what is stand is sounds like it is near the exhaust elbow back of the CLY head is that possible?
I added antifreeze yesterday no loss at all 2 days on the water so it could be a slow leak for the hose that goes from the exhaust manifold to the intake manifold. I did a head gasket about a month ago. I fixed the carb link issues

 

[Scott Danforth]

If you didnt use a mercruiser head gasket, you will have problems

Since you already stated you ran the motor to 190, you most likely spit the head gasket. The 470 with its aluminum open deck block and iron head does not tolerate more than a 10 degree overheat

Drain the cooling system

Do a compression test, all cylinders should be between 140 and 150

Do a leak-down test

Pressure test the cooling system and follow the hissing to find your leak

Since you didnt state you have coolant in the oil, It may be the exhaust manifold, it may be the head gasket.

​​​​​​​If you have coolant in the oil, check the cam snout seal

 

[kenny nunez]

There is a small core plug that seals off the exhaust that is used when the head is on a 385 series Ford engine. It is for the air injection pump for emission control. There is an identical plug in the front of the head also. The easy fix is to use the front of the head to fashion a cover plate with a hole for a short 3/8” bolt to hold it in place. Fill the cavity with some RTV before the plate gets mounted.

 

[karayj]

I will definitely run a compression test I don’t mind doing another head gasket next spring it was a pretty simple job the boat is running good I’m gonna leave well enough alone to enjoy it another 40 days.

can someone explain to me how to fix a possible vapor lock issue today I started the boat at least 12 times to move because of drifting towards an island everything was fantastic once or twice I started the boat drove it for about two or three minutes to a new spot everything ran fantastic idled no problem. Then heading in my daughter wanted to go on a few long runs I’d say about 20 minutes of continuous driving when I got to the dock it was a lot of traffic someone was saying something to me so I had to shut off the engine to hear what they were saying. It was a nightmare trying to get it to run at idle every time I put it into gear it would stall. I ended up giving up and just walking the boat along the shoreline 20 yards to the boat ramp. I should’ve never shut it off it was running fine