I have a 93 civic EX 1.6 vtec. 118K. Auto.

Car has had this leak since I got it. It seems to have a wet spot on the passenger topside of engine. Almost like it could be behind the thermostat housing. It seems like it could be coming from under the head but the car runs fine. No white smoke or oil in antifreeze or vice versa. The sensor bolted to thecyl. head next to the intake manifold (what sensor is that) seems to have some coolant on it.Does this sensor have any oil or antifreeze going into it from the head? I am thinking of unbolting this sensor and putting some liquid gasket in there.But i'm not positive that the leak is coming from there. I don't think any of the hoses are leaking either because they seem dry at the connections. And I think this IS coolant because oil wouldn't look as clean and it would attract more dust.

Also, when I rev the engine between 1500 and 2000 RPM I can hear a knock from what seems to be around the under side of the intake. Could it be that motor mount behind the engine? It doesn't make the knock except when i'm crusing along at like 20 mph and the engines not working hard and it's just kind of freewheeling at 2000 rpm.

 

Both of those sensors screwed into the head have coolant behind them. The one with one wire drives the temperature gauge on the dash. The one with two wires tells the ECU the coolant temperature. There is also coolant flowing thru the intake manifold. The intake manifold gasket near #4 cylinder has a coolant passage and it is possible coolant could leak to the outside there.