Hi all.. so yesterday my b16A started to misfire randomly. Never had any issue with the engine prior. Oil pressure and temp had always been doing good. After the random misfiring, i decided to check the plugs. To my horror, i found coolant in cylinder 3 and 4.

Question, any idea how coolant might had made its way into the spark plug well? Im pretty sure the head has no crack since the engine was still running pretty well, no knocking or mechanical noise of any sort. And yes, the plugs were pretty tight when i was removing it, so for the coolant to flow upwards thru the threads of the plug is pretty impossible.

 

I've not seen the b16 head design. But the only way I can think coolant would be on top of the plugs (well side) is a cracked head.

You probably won't know anything until you pull the head and have it pressure tested.

 

Got my car towed to the workshop..head's gonna be out tomorrow i guess. Am gonna be so fustrated if the head is cracked ;( especially i dun usually abuse the car. Its my daily, seldom visit VTEC zone. Was secretly hoping that someone would tell me its the intake manifold gasket or something that doesnt require that much of a work ;p

Anyway i still cant visualise how coolant can go on top if the plug.. and it was pure coolant, no oil. And the oil dip stick doesnt show sign of coolant mix, no smoke at tail pipe, no overheating

 

Generally a coolant passage will flow through a DOHC head over top of the combustion chamber and around the walls of the spark plug holes. I'm not 100% positive this is the case with a B Series head as I never cut one in half but I don't see any reason it wouldn't be. This means coolant is flowing against the walls of the spark plug holes and a crack can result in coolant leaking above the spark plugs. If this is the case, it is highly unlikely it is fixable and because the walls of the spark plug hole support the combustion chamber, it would only be a matter of time before a larger failure would occur. Pressure testing the coolant system would be my first step followed by fully draining it and pressure testing again using soapy water to look for cracks.

Here is a cross cut section of a Miata head and you can see the coolant passage:

https://www.miataturbo.net/attachmen...e-dsc00704.jpg