I have searched through many threads looking for troubleshooting ideas but I haven't seen any other threads with the same problem. Any help would be greatly appreciated.

I have a 1997 150 4.6l with about 230,000 miles on it. The only work done to it within the past year has been oil changes. Plugs and wires were changed about 2yrs ago.

A few days ago I went out to start my truck and the it idled a little rougher than normal. Each day it seems to get progressively worse. Each time after about 30 sec to a min it runs fine. I drive on a hwy 30 min to work, stop a few times and its still fine. Tonight I waited about 2-3 hrs after the drive and started it up and it ran a little rough but not as bad as when its been sitting for 8+ hrs. On a side note I have been loosing coolant, about 2 gallons over the past 5-6 months. There are no trouble codes and there has not been any other problems.

Thanks for any help.

 

You need to find out where all of that coolant is going, could be part of the problem.
Could be a head gasket, intake gasket, heater hose leaking on #4 plug, or even the water pump. Do you see any coolant on the engine, or under the truck?

 

Time for a compression test and a hydrocarbon test on the coolant.

 

I had a similar issue, only the idle would be really rough after travelling a bit (sitting at stop light). Turned out to be the head gasket leak. Ended up costing me an engine (bend rod).

 

my bet is head gasket.

 

I have looked everywhere for a coolant leak and have found nothing. I went and bought a big metal pan since my yard is all rocks to help determine if there is a leak but nothing was on the pan after a long drive. The problem never occurred when I was stopped or when engine was hot. The past few days however I haven't lost any coolant and the problem has stopped. I have also noticed that after having my truck sit for a few days there is still a lot of pressure in the coolant reservoir. Would this pressure go away if there was a leak or would the leak occur only when the truck is running and at a certain temp?

I plan on doing a tune up on the truck soon so I was thinking on doing a compression test right before. Can some one direct me with a link to a page that gives the info on how to do the test and what the readings should be on each cylinder. Also can someone post what the pressure should read for coolant reservoir?

Thanks for all the info so far.

 

Go to the parts store and see if they rent a hydrocarbon tester for the coolant. Your leak appears to be internal, which is likely a head gasket.

 

Flash a light down in the block valley. - Behind the alternator. Allot of coolant can collect there, then splash out once driven.