Hey guys, this is definitely one for the V10 forum. I have a mystery coolant loss problem and I really hope it's not the worst case scenario. Last week I did a routine fluids check and noticed the coolant in the reservoir was low....so I added a gallon and got it back up to the full line. Drove like 50 miles over the course of the week and checked it again. Down again, but not as much. Added a little bit. Back to the full line. Drove it 300 miles round trip and got home and there was almost nothing left in the reservoir. Topped off again and took almost a gallon and a half. I just changed the oil recently and I didn't see any signs of a dreaded head gasket failure...has plenty of get up and go....no oil loss or any other visible signs of a leak or burning unless I'm not looking in the right spot...the ONLY weird thing that happened is yesterday I drove the truck to the store and as I'm walking back to the truck I notice the right shock is wet so I popped the hood and there was coolant around the reservoir tank cap...like it burped. Also, at startup I have noticed a "sucking sound" like water being sucked under the dash board near the passenger side of the truck. Any insight on things I should look at/test to narrow this down and get it fixed would be appreciated. Thanks everybody.

 

Have the system pressure checked and go from there.

 

Your problem reminded me of a similar issue I experienced when my truck was then only 3 months old . I had noticed some antifreeze spills around reservoir ( A/C components , front of the engine ,etc ) . Took it to dealer , they diagnosed as a "bad reservoir cap " . They changed the cap and that fixed it , that was about 10 years ago . Hope yours is as simple as mine.

Good luck,

 

I would be thrilled if this is all it is. It's just so disappointing cause the truck runs great otherwise and I've had it about 6 months now and this started all of a sudden. It may be leaking more than I'm seeing, too. I really don't know. But a gallon of coolant in 300 miles seems like something is definitely wrong. I'll get a new cap and go from there and get it pressure tested.

 

Mine was having the same issue, it was low on coolant after each trip but I couldn't find a leak and feared something worse. One day I was looking underneath and noticed the lower radiator hose has a plastic piece in the middle where the hoses to the oil cooler connect. Plastic rings are used instead of clamps to hold the assembly together and one of them cracked and lost its clamping force. I put a regular hose clamp around the outside of the ring and I haven't had to add any coolant since then.

 

*Update*

Had some time today to go outside and try a few things. After the results, I'm even more confused but I'm hoping these happenings will spark someone.

Started with the easy stuff and checked for leaks. Nothing that I can see is leaking. No hoses, not the radiator, water pump, nor inside on the passenger side (which I heard is common with the symptom I had of the "sound of water under the dash"). Decided to see if there was air in the system so I took the cap off the overflow tank. Started the truck and let it get to operating temp then replaced the cap. Prior to doing this, I had not refilled the coolant from the previous time I drove the truck so the overflow tank had just a tiny bit of coolant sitting in it (probably down about a gallon and that was in 300 miles). By the time it got to operating temp and I replaced the cap, the coolant level had completely reached the full line. Hmm. Seconds later, the temperature gauge pegged on H and the truck seemed to "idle down?" Ugh now I'm really lost.

 

Could the coolant be leaking into the oil pan---have you checked for that yet? (If that's a dumb question sorry but without signs of leaks on the ground or anywhere else on the chassis few other places it can be going.)

There has also been issues with the hard coolant line locating partially under the intake manifold. That typically gives off the smell of raw hot coolant.

Hope its not a blown head gasket or other crack in the block.

 

Well I mentioned in my first post when I started this thread that I had just done an oil change and there didn't seem to be any coolant mixed with the oil. But as for my latest update in my last post, it is just mind boggling that when I took the cap off to let potential air out of the system that the coolant reservoir filled completely back up! So it makes me wonder if I'm really losing coolant at all or if there really is just air in the system. I mean where was a gallon of coolant hiding that it filled my reservoir back to full? Or perhaps as a few mentioned earlier a faulty reservoir cap not holding pressure?

 

I forgot to mention that when the truck pegged on "H" on the temp gauge and idled down it also tripped the CEL right before i shut it down and when I started it back up temp gauge was normal and wasn't on reduced power anymore code was P1299.

 

In my opinion, The water coming out of the engine and going into the degas bottle was not replaced by enough water (you said it was low) and sent your truck into limp mode. 1299 is cylinder head temp. In reading the ford shop manuals for your truck it says "Never remove pressure cap while engine is running." To 'burp' the system you should fill the degas bottle to proper level and then start truck and run to temp with heater on full hot blowing thru the dash vents on high. Then let it cool back down and add water as needed. Did you replace the cap with a new cap? Did you pressure test the system. Are you smelling anti freeze at all when your driving or while it's running in the driveway? I had a small leak that ended up being the intake manifold gasket. For a while I could not see it but I could smell it. After removing the intake manifold I found that both ends at the water in/out were cooked. Also did the t-stat with a factory new one.