Just happened to notice today while looking at the engine after turning it off, I saw some tiny bubbles coming from behind the bolt head. This bolt is located just below and a little to the right of the thermostat. I also included a close-up photo. Looks as though it's been leaking for some while. Any recommendations?


This is a 1995 F150 I6 Manual with 177,xxx miles. Thank you for any recommendations.

 

That looks like the timing cover. If it's bubbling at that bolt your thermostat housing is probably leaking and coolant running down onto the cover bolt. I don't think the bubbling is coming from the timing cover.

 

Well, I felt all around the thermostat which was replaced about 6 months ago. It's dry as a bone. Doesn't appear to me at this point something is dripping on top of the leaky, bubbly bolt.

It looks really gummy and oily in that area and for sure tiny bubbles are coming from that cover at that bolt. Even after I shut the engine off I could watch a little bubble or two bubble up from that cover (assuming it's the timing cover). I'm still stumped. Should I maybe snug up those bolts some?

 

Snug it up a bit. It's possible I guess for it to get hot enough to bubble oil. Make sure your PCV system is functioning properly. That's not a spot I would think oil would just run out of unless the gasket wasn't compressed enough AND pressure was building up in the crankcase. Does it leak anywhere else?

 

I need to replace the oil sending unit as it's leaking oil from there, so I'm not sure if there's leaks from anywhere else.

 

Its hard to tell from the pic but that couldn't be the water pump could it? I replaced mine not too long ago because it was leaking.

 

Bubbles mean pressure is building up - so pcv as mentioned by ncranchero. Crankcase areas should (theoretically) be at negative pressure with the motor running.
You can tighten the bolts a little, but I'd address the pcv system first. If pressure is building up, it has to go somewhere - most common place is the rear main seal. #1 reason why they leak.

 

I agree check the pcv valve and the vacuum hose. I am unfamiliar with the pcv on an I6 but on my 5.0 the fitting on the rear of the intake for the pcv was almost plugged up with carbon so check that for sure. If you replace the pcv valve get a motorcraft, much higher quality than other brands and fit much better as well.

 

The PCV was replaced last summer after I bought the truck. I don't think any of the vacuum lines were replaced by the mechanic I brought it to for a tuneup. Replacing the vacuum lines is on my list of things to do, but I'm slowly learning how to do everything myself from this forum and YouTube :-)

One other item of note - after the engine is shut off, I can see the tiny bubbles forming behind the bolt head for a good minute or so. So, you're right, there is pressure in there for some reason.

Is this cover (below and to the right of the thermostat) the crank case cover?

 

Timing chain cover