Engine Overheating After Re-Installing Intake Manifold (2011 Buick LaCrosse 3.6L)

I recently had to replace a couple of ignition coils and spark plugs in Cylinders 3 & 5 to fix I misfire I had. The coils for 3 & 5 are only accessible by taking off the intake manifold on the 2011 3.6L V6.

Putting everything back together took a while because I snapped the PCV line (don’t know why these are cheap plastic), but I eventually replaced the PCV line with a OEM part. I took a drive around my neighborhood afterwards & although I cleared the misfire and all of my codes, the engine was starting to overheat within 5 minutes after a cold start.

I opened it back up, lo and behold, I saw the connector on the Coolant Breather Pipe (pictured below) was snapped as well. While I wait for that part to arrive, I simply just crimped the hose to where it leads, to hold it over for a couple of days… Started it up, and overheating just the same.

Did I do something wrong when re-installing the intake manifold, or would it have something more to do with the Coolant Breather Pipe? Admittedly this is my first time having to take off an intake manifold on any car, but I made sure I payed attention to important parts such as the manifold gasket, etc… Really would like to solve this without having to take the car into a shop.

Very possible there is still air in the cooling system. How did you refill the coolant and “burp” the system when you were done? The coolant bottle cap needs to be off and the heater needs to be set to “heat” at the least.

Some cars are harder to expel the air than others. You may need several heat cycles to get all the air out. You may even have a bleed nipple at the highest point in the coolant system to let the air out…or you may have to loosen a hose.


Well you may have just got me on that one, I actually never burped my system after replacing everything before I tried to drive it. Went and took a look, and coolant looks pretty low (it wasn’t before I did all of this).

It just started snowing here & my car is parked outside, so I’ll get back to it tomorrow, and with an update on the burp… Quick question, is burping needed basically every time the intake manifold comes off?

Yes, because you drained the coolant. Burping is needed every time you drain the coolant. Start the car with the coolant pressure cap off, fill it to the cool line, let the engine idle and warm up, the coolant level should drop a little more as the thermostat opens, add more coolant. When it stops dropping, put the cap back on, drive it around a bit then park it and let cool. Check the level again. Add as needed. At this point you should be able to drive the car normally but keep checking the coolant level until it quits dropping.

You have blocked the coolant circulation, that line vents air/coolant from the top of the engine. You will need to replace that line to be able to properly refill the cooling system.

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I didn’t actually drain all of the coolant out of the system. At least properly, in the way that you would flush your system. However, it definitely explains why my coolant reservoir looked basically empty afterwards… Any idea where that coolant is? It hasn’t leaked out of my car, so I’m assuming it’s still in the system.

I think the coolant leaked onto the road when you drove with the broken coolant line.

Of course you didn’t drain it all out. Why would you? The coolant bottle only holds a small amount of coolant, the rest is in the engine block and heads. Given our exchange here, check your oil level, too. If it is INcreasing and the oil is looking like a chocolate milkshake, you did not properly seal the intake manifold’s coolant passages and coolant is leaking into the oil.

Thanks for the replies Mustangman & Nevada_545. I’ll be back with an update in the next day or two, so we can finally mark this thread as “fixed”.

Plastic intake manifold plenum, I don’t think it can leak coolant.