I've looked thru several threads, though they were years old. I have a 2004 F-150 4.6 4x4 STX. All was good with the truck until last year when I hit the 150k mark. I've changed countless coils and plugs and have read how coolant leaks from the intake can cause those. That I'm familiar with. Last Friday I drove home from work and as soon as I opened my door I smelled antifreeze.. Took a quick look around and saw a constant stream coming from the back of my engine. I could see it pouring around the starter but couldn't quite find the source. I popped the hood and looked around and behind the alternator I saw a lake of fluid under the plenum. After reading the forums I was sure it was the hose running in that valley. But a later post towards the end of that thread pointed towards a freeze plug. Thought this to be odd seeing as it just happening this far into summer. As I pour water in the reservoir, within seconds I can see it flowing to the ground. I'm an electrician, not a mechanic. I can do mechanical work but am often limited by tooling. Any recommendations as to a fix and if a guy with decent mech skills can do such a job without making the issue worse? Any help would be greatly appreciated!

 

You might possibly have 2 leaks. Normally the hose, if it leaks, has coolant leaking from under the alternator. That's a reasonably easy fix and a common failure. If you have coolant coming out of the rear of the engine, it's most likely a freeze plug. You have two on the rear of the block. You will drop the transmission to replace them. On a 4x4, as I recall, the engine has to come loose, not out, just loose to let the rear of the engine down some to get a better angle on the plugs. You need to know, generally when one freeze plug is bad, they all are bad. They rot from the inside so a visual inspection from the outside tells you nothing. I'd strongly suggest replacing all freeze plugs.
Summer time is when a cooling system is working the hardest. Any weakness in the system is going to show up in the heat of the year. Considering you have 150,000 miles on the engine you likely are getting some blowby of combustion gases which will lead to higher internal temps. You won't see it on the temp gauge as it's telling you the coolant temp. Make sure the PCV system is working right and use a low NOACK oil. You can find the ratings at PQIA but to cut the correct answer, the Pennzoil conventional 10w-30 has the lowest ASTM D 5800 and beats the likes of Mobil One by being 3 times stronger against high heat. At your mileage you need all help you can get to keep that engine running longer and better.