Hey all, I'm pretty sure my cars intake valve seals are starting to go out. It sat for 5 days, and when I went to start it, it misfired for about 5-10 seconds with a pretty strong oil smell out of the exhaust before stabilizing and the smell going away. Should I just send it and top off the oil? The car has 284,000 miles, and aside from that it runs beautifully, and is cosmetically very clean and rust free (aside from the crossmember, which I need to replace).

I'm taking this car to college and I need it to last for the next 4 years for context. How bad is a valve job? I'm quite mechanically inclined so pulling heads isn't very scary, I just need to do it on a budget, and before august. Would I be better off just replacing the motor altogether? (PFA)

 

Short answer: I'd replace the engine and be done with it.

Long answer: Technically, the intake valve seals can not be replaced individually. In fact, Nissan does not even have parts available for the intake valves at all. That, and the added complexity of removing and reinstalling/syncing the VVEL ladder assembly alone makes this a time consuming job- and likely a costly one at that.

Used, low mileage engines are plentiful and the swaps painless on both budget, time, and body.

 

The first thing you need to do is figure out if it indeed is valve seals.

One of the ways you could do this is to pull the intake manifold to inspect the actual valves to determine if they are leaking past the seals.
Secondly install a catch can in between the PCV, it's quite possible that at almost 300k your cylinders are a bit worn increasing blow-by which the PCV pics up and sends towards the intake to consume.

Start with determining how much oil you are actually consuming first, a dirty PCV system will introduce even more oil. In other words the oil you consume today might be residue from the week before that stayed inside the Valve covers.

Your diagnosis of smoke at start up could point to valve seals as well as a dirty PCV mechanism that once engine is off it drips oil into the intake. Only removal of the intake will show which one is more probable.

Lastly the 3.7 uses an aluminum cam ladder design that holds your intake's eccentric cam which needs to be removed to access the seals. This means removal of the entire mechanical VVEL system, doing so requires re-setting of the VVEL position sensors so an extra 2-3 hours on top of what an average valve seal job would cost.

Shop around to get quotes to determine how much you'd actually spend on this, while you're there get quotes on engine replacement.

Why engine replacement? - Total price.

3.7s are so common in the infinity line that there are plenty out there between $800-$1000 + labor which can range about $1500-$2000

Valve require an almost complete disassembly. Front and rear timing cover, removal of chain, gears, cam ladder assembly just to get to them.
OEM seals average about $100 + the rest of things they discover while they are in there.

All of this surrounds the competency of the technician, especially when such a heavy fix is involved.
Asking 4 more years out of 300k would include a water pump, gallery gasket, possibly a VTC gear or two, possibly some coils and other work as well.

This is where a newer Q50/M37/Ex37 engine would be a better option. Most of these come with under 100k miles and Gallery gaskets that are intact. Most mechanics are able to tackle engine replacement, confident in saying that an engine replacement will last you much more than those 4 years. The cool aspect of it is that you can strip your older engine for sensors/switches/parts to keep extra in case you develop issues with the new one. You could even sell your older motor and get $100-$300

 

Thanks for all in input. For now I'm gonna replace the plugs, and PCV valve + clean out the intake, as when I pulled my MAP sensor there was a decent amount of oil on it. I'll track the oil consumption over the next month.

 

If there was significant oil in your system then this follows more towards blowby from age. A catch can might solve these oil burning issues.

How much are you consuming per 3k miles?

 

Honestly, I'm not quite sure. I'm probably gonna run slightly thicker oil to help with the blowby and close the ring-to-cylinder gap when I change the oil this weekend.

 

This is a good tactic. In all honesty I've ran 15w-40 rotella oil for when I had Gallery issues and it decreased the oil leak I had in the oil pan so in theory it could work for you however keep in mind that you're see snow climates which can make this problematic being that thicker oils tend to take longer to warm up and flow. It's worth a try, 10w-40 or 15w-40