In late June of last year, I was driving to Orlando. Upon coming out of a toll booth, I gunned it to beat everyone else because we all know everyone else drives slower than us . Anyways, I noticed in the side view passenger side that there was a trail of smoke/water/steam behind me. I was only a couple miles from my destination so I thought maybe I could make it; that was when limp/failsafe activated. Upon pulling off the shoulder, I found that my upper radiator hose had popped off. I bought this vehicle a year prior to that knowing it very, very slowly lost coolant through some means, but I couldn't pinpoint it. My hypothesis was that I lost enough coolant to make the engine heat the water hot enough to pop the hose off. Ever since then, I've had a massive coolant leak that would amount to about 1-3 gallons a day. I put some head-gasket sealant in it just so I could drive it, as it's my only daily.

My question is, would the limp mode activate before I overheated it, or did I definitely overheat it and screw a headgasket? It runs like a champ. No different from before I popped the hose off and started leaking like no tomorrow. I had a guy tell me that he had similar problems from 2 of his tenth-gen F150's and his first gen Expedition, and it turned out to be a cracked plastic intake on all of them. I'm hoping it's the intake manifold, as it burns coolant now and there is coolant in my intake valley. What are the chances everyone?

2000 Expedition 5.4 Eddie Bauer by the way, I posted in the F150 forum because I know more people own those, so maybe I'd get a faster response.

 

Coolant does not burn, only changes Phase, passes through and could kill the cats, if that is the case.
There is a coolant line that goes through the block valley and come out the back..
You will just have to locate the leak.
Keep running it like this and you will do damage to the engine.
The limp mode is the result of the CHT detecting the overheat condition after there is coolant loss.
The hose blowing off could be either from over heat or a head gasket leaking cylinder compression into the cooling system.
Good luck.

 

Well this isn't any fun. I didn't literally mean burning coolant, just changing it from water to steam. I knew limp mode was detecting overheat, but wouldn't limp mode prevent it from warping a head/blowing a head-gasket? Isn't that it's very purpose?

 

It's not foolproof.

 

Yeah I had a feeling. Since I have the plastic manifold that doesn't have the metal crossover, I'll go ahead and replace it with the newer style and gaskets and what have you. While I'm under there I'll check the tube coming out of the water pump and around the passenger side bank for leakage. Guess I'll do all my heater hoses while I'm in there.

 

Before you go through all that, do a compression test and test the coolant for hydrocarbons.

 

Will do