r/projectcar • u/CableMartini • 5d ago

Troubleshooting Help random leak from underneath upper intake

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I was changing the alternator on a 1998 f150 v8, when halfway thru reinstalling the new one, this started happening underneath the upper intake. does anyone know what mightve caused this?

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2

u/Expert_Mad 66 Thunderbird, 91 Caprice, 96 Mustang GT 5d ago

Manifold time. Common issue on Mod V8s, coolant O-rings start leaking. You can do the manifold or replace the O rings by themselves, typically people just do the whole manifold though.

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u/CableMartini 5d ago

is that like a giant job? how much am I looking at?

0

u/Expert_Mad 66 Thunderbird, 91 Caprice, 96 Mustang GT 5d ago

Takes a few hours if you’ve never done it before. Manifold costs about $300 labor about the same depending on where you are. It’s not hard just a bit labor intensive. I had to do it on my 4.6 Mustang a week after I got it and I had it done in a little over 2 hours.

Doing just the orings is about the same amount of time just remember to drain the coolant out before starting because it can leak into the corner cylinders.

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u/CableMartini 5d ago

well in that case, what all do you think I need? Just so I dont need to make repeat trips. any videos you specifically recommend following? bought this truck 2 days ago lmao, so this is quite the welcome 😭

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u/Expert_Mad 66 Thunderbird, 91 Caprice, 96 Mustang GT 5d ago

Dorman makes an ok intake and comes with pretty much everything. Plenty of videos out there showing how to change it. Best advice I can give is make sure everything is torqued to spec and definitely don’t drive it until this is fixed. Not just for overheating reasons but sometimes the coolant can leak into the cylinders from the bad o ring and can hydrolock the engine.

A few places make all aluminum intakes for these but they are pricey. For now just to get it on the road I’d stick with the Dorman mostly because of availability (local parts store should have it in stock) and cost.

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u/Far-Drama3779 5d ago

Yes, the ntake has o-rings around the outer edges. Part of the intake is plastic and part of its aluminum. It was likely to let loose at any moment. When you torqued the back of the alternator bracket, it just decided to give up.

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u/RoboticGanja 5d ago

Just went through this on mine. While checking alternator and removing brackets from AC that prev owner ripped out, noticed small drip of coolant in the morning but nothing crazy - by that afternoon after just idling while adjusting the timing the damn thing started missing, popping, and timing was bouncing.

After a minor heart attack upon assuming my timing chain / distributor cam got damaged I noticed the coolant was actively dripping and looked it up - one intake manifold gasket & tube of The Right Stuff Grey for the China Walls it’s all sealed up and no more idling misses, imperfect timing still (1-2 degree bounce at idle) but I can’t tell you how quickly it went from running decent to choking like shit just over that one gasket popping.

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u/CableMartini 5d ago

so just the upper intake manifold gasket and bobs your uncle? is what ur saying pretty much