Hi I have a 2000 Ford F-250 with a 5.4 triton, I have been getting weak starts for the past few days so I replaced the battery yesterday, while I was replacing it I noticed brown sludge in and all over my coolant resovior, I replaced the battery and still got a weak start thismorning, what could be the issue? Also are the weak starts and coolant sludge related? I did some research and it seems the coolant sludge in with this motor is a pretty common problem and flushing the coolant system should handle it, but I could not find any issues with this problem being related to weak starts, please please help
P.s. I do all the work on my truck with my dad and I'm a high school senior I can't afford to take it to a shop

 

It would be a good idea to invest in a multimeter and watch a few videos on voltage drop testing. Multimeters are not expensive and once you learn how to use it you can do voltage drop testing of the starter circuit. You may find corroded battery cables or other causes like poor connections or a defective starter and it will save you much time and money doing your own testing. Once you confirm that the starting circuit is good you eliminate that as a possibility. Do you think you would want to try that?

 

Being a 2000 with brown sludge sounds like the coolant has never been changed. In the late 1990s - early 2000's, Ford put BARS Stop Leak in the cooling system at the factory (hence the brown sludge). I flush my cooling systems out every 4 years or 50,000 miles. I use good ole' green Prestone (the non 50/50 mix) antifreeze. I disconnect the hoses for the radiator and heater core. Then I forward and back flush several times. Then I add 50 of the capacity with 100% antifreeze and then top the system off with distilled water.

 

Okay so I solved the weak start problem, some bad connections, but the antifreeze sludge is still a problem, is flushing the coolant system a difficult job? I watched some videos on it but I'm not sure how bad it will be with all this thick sludge

 

Vehicles with rear heater cores are the hardest. Being a truck, yours is straight forward. What I do is use a bottle of Prestone® Radiator Flush + Cleaner and water like the directions say. Then I drain everything out. I disconnect the heater core hoses and take a garden hose and forward and backwards flush the heater core 4-5 times. Then I disconnect the lower radiator hose and put the garden hose in the lower radiator port and fill and empty from there 4-5 times. Then I blow thru the heater core with my mouth to get out as much water as possible. Then I disconnect the lines going to the coolant tank and clean it out. Reconnect everything, I then add 50 of my cooling system capacity with plain ole' green ethylene glycol Prestone® Concentrate Antifreeze/Coolant and top off with distilled water. Put the heater setting to hot and fan to high, then drive around for about 25-30 miles. Let set over night and bring the radiator tank to the FULL COLD level with distilled water. This will give you a true 50/50 mix. Your vehicle will require about 2.5 gallons of straight coolant.

Remember that Ford DOES NOT have any procedures for and does not recommend using recycled coolants like some dealerships use when performing their so called coolant flushes.