Head gasket - you’re smart, I’m stupid

[03yllwguy]

Friends, request guidance for the mechanically impaired.

Vehicle: 2003, 117k miles, daily driven since Dec 02, pulley tune only.
Symptom: quarter size coolant leak on the floor after longer drives & oil cooler soaked in residue and dirt (noticed it since under the car a year ago).

Assumption: oil cooler needed rebuilt with new gasket.

Reality: identified a 1” length section of my head gasket that appears to be leaking

- I have NO oil in coolant nor coolant in oil
- Car runs fine, plugs are clean, no other issues than coolant on the floor infrequently

- Compression test as follows:
1) 165psi
2) 170psi
3) 175psi
4) 165psi
5) 145psi
6) 150psi
7) 155psi
8) 170psi

Question:

- How can I have a leak and still pass a compression test (I assume these numbers are reasonable for a 117k mile car)?

- Considering the aforementioned details, is this critical? Likely to spread?

Thanks in advance

 

[P49Y-CY]

I doubt that that's a head gasket leak. I think it is seeping out from the front cover where the dab of sealant goes.

 

[01yellercobra]

I've seen head gaskets weep on some of the older 4.6's. It can leak coolant or oil and still have a good seal around the cylinder.

I would pick up some UV dye and figure out where the leak is coming from.

 

[DSG2003Mach1]

when I popped a head gasket on my lightning it leaked out like that but it would also randomly run very hot for a minute or two (like it had an air pocket) then it would clear and be fine. I never compression tested. Cylinder 5 isnt super low but its definitely lower than the others.

as for leaking from behind the timing cover - Im not aware of any coolant passages behind the cover, oil but not coolant.

 

[P49Y-CY]

as for leaking from behind the timing cover - Im not aware of any coolant passages behind the cover, oil but not coolant.

My bad, I was thinking oil leak

 

[StrayBullitt]

I'd clean up that area and jack it up and let it idle, see if you can tell for sure where the leak is coming from. Sometimes the leak isn't bad enough to affect compression, and it may only under certain conditions.

 

[03yllwguy]

Thank you all for the replies.

Ran a compression test on coolant system, passed.

Ran dye test on oil, passed.

I have a suspicion it may be the water pump which may happen to be leaking down at this particular spot. I sat under the car for a while after cleaning it with a power washer and it running and I can’t see anything leaking directly from this spot, but the WP is leaking.

Thanks for the help. MTF.

 

[BlckBox04]

#5 cylinder looks a little concerning on the compression. I wouldn't classify it as a problem but just keep that in the back of your mind.

 

[hotcobra03]

Anything under 160 would bug me.

I had cyl 7 crack. It read 145.

I’m more into the head causing the issue vs gasket.

The oil cooler to block gasket is a common leak for coolant

Are you losing any coolant?

Mine was blowing out exhaust
I noticed after I turned off engine wait 3 mins and white steam would only than show out exhaust

I noticed when I went to replace head the exhaust on that side was rusty inside

Car ran fine till after a 45 Min drive

It would start to over heat. Any short drive you never now it

 

[03yllwguy]

Hotcobra03,

Thanks for the info. I replaced the water pump yesterday, power washed the area and am replacing the seals/gasket for the oil cooler today.

I looked back at my historic compression test results and nothing has changed in the past three years?

I am NOT losing oil. I am losing coolant, ever so slightly. Car is a daily driver and has never overheated, drives are often over 45 minutes.

Thanks again for your thoughts.

 

[BlckBox04]

maybe you should do a leak down test to see if the rings on #5 are warped