Merc. 7.4 smoking from breather hoses
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=38585
Printed Date: October-07-2024 at 10:28am
Topic: Merc. 7.4 smoking from breather hoses
Posted By: jonas
Subject: Merc. 7.4 smoking from breather hoses
Date Posted: May-08-2016 at 2:39pm
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Hi all. I just purcased a baja force 250 to use when we are to many to fit in the mustang. I thought i'd post here as I have always found the answers i neded. It has a mercruiser 7.4 gen V with alpha one drive. Seawater intake through the hull. Edelbrock performer intake 2,0, new edelbrock 1410 marine carb, new exhaust manifolds and risers. It has through the hull exhaust tips with silent choise New impeller and housing. New oil and filters. When i run it on the hose it runs fine with no smoke from breather hoses. No smoke from exhaust When i pull the oilfiller cap while running there is no puffing or smoke/steam. When i put it in the water it starts to smoke out of the breather hoses after 5-6 min of running at 3200 rpm. If i run it at 4600 rpm for 3 min or so it vil smoke so badly that i have brown smoke comming out of the enginecompartment and the engine loses power, if i open the hath a little so the smoke can clear the engine dose not lose power. After a 4600 rpm run i have a little oil blown out of the dibstick. When i come down to idle to go back to marina the smoke keeps blowing from breather hoses. Low rpm = little smoke high rpm = lots of smoke. Engine runs very well the hole time. You can put a glas of beer on the intake with out it shaking at all. Compression test. 152 152 148 152 150 142 148 152 psi. Oil dose not show signs of water on the dipstick. There is a little tan oil goo in the filler cap and breather hoses. The right side exhaust is steaming and the left is not when in the water both risers are cool under all rpm. Engine tep. 160 Oil pressure ca. 40 at idle |
Replies:
Posted By: jonas
Date Posted: May-08-2016 at 3:05pm
 
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Posted By: GlassSeeker
Date Posted: May-08-2016 at 4:21pm
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My guess: intake gasket leak...leaking water to intake...could be head gasket ...fact is water is getting into the engine it should not steam at all...I'll bet ya got peanut butter in the valve covers...its not condensation either ------------- This is the life |
Posted By: MrMcD
Date Posted: May-08-2016 at 4:45pm
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Make sure your crankcase vent is functioning. Under a load an engine will have more blow by pressurizing the crankcase more. If it can't vent it will build pressure, it might pop the dipstick tube up to vent the blow by. Maybe when the Edelbrock was installed they never vented the engine correctly with a PCV system. Your compression numbers seem well within normal so your rings and valves are working. It also shows the fire rings around each cylinder on the head gasket are sealed. With these items sealed the only other possible issue for compression reaching your cooling passages would be a cracked cyl head with the crack opening under load. The intake gasket could be a suspect for letting water reach the intake port close to the coolant passage. Could cause steam in your exhaust. Pull the spark plugs and see if some are steamed clean. If they are you found one problem. When water leaks into a cylinder it will steam blast the piston, head chamber, valves and spark plug clean. All the other piston tops will be carbon black. Smoking under a load, blue smoke would be blow by not steam. |
Posted By: jonas
Date Posted: May-08-2016 at 5:08pm
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The two hoses from the valve covers are not blocked they mount on the flamearrestor on the original bracket so I think that i how i should be. Sparkplugs all look light tan with i little carbon buildup on the buttom. I have had a camera in each of the cylinders and they all look the same colour I will remove the intake manifold tomorrow and see how it looks. |
Posted By: GlassSeeker
Date Posted: May-08-2016 at 7:01pm
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That breather set up by Merc is the same on the 5.7 350...I've been thru what you are about to start...gonna spend alot on oil changes alot of time resealing the intake in hopes of it solving...being able to see the problem...when you pull the intake its very difficult to tell if it was the intake or not....how many hours on engine? You may just want to go right to rebuilding it ------------- This is the life |
Posted By: tryathlete
Date Posted: May-08-2016 at 11:18pm
| I know this sounds silly but is it possible the crankcase is overfilled and you're slinging oil all over the place at higher RPM's? |
Posted By: jonas
Date Posted: May-09-2016 at 5:05pm
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I sucked the oil out of the engine today there was only 3,5 liters left in it. The PO told me that the engine has 300 hours on it. I will tear it down this weekend and report back what I find. |
Posted By: jonas
Date Posted: May-21-2016 at 2:43pm
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I pulled the intake of today, there is a lot of grey goo i the v of the engine but I see no sign of water in the oil I suked out of the oilpan. There is a little corrosion on the gasket surface on the intake near the water chanel.  
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Posted By: tryathlete
Date Posted: May-21-2016 at 9:50pm
| So for certain your steam is coming from the intake leak. Assuming no milky oil got into the crankcase for spreading the disease, maybe you'll get this thing back on the water escaping the dreaded overhaul. My fingers are crossed. |
Posted By: jonas
Date Posted: May-29-2016 at 8:38am
| Took the heads of today, no clear sign of crack or bad gasket. I will drop them of at the engine shop tomorrow and see what they find. |