Spark plugs. Should I or shouldn't I ??


Asked by Jul 21, 2017 at 08:10 PM about the 1999 Ford Expedition 4 Dr Eddie Bauer 4WD SUV

Question type: Maintenance & Repair

I have a 5.4 engine, 99 ford expedition. Going to canada in a month towing
a boat. Engine is running good, but its been 5 years since I have changed
spark plugs, 35,000 miles. Would you think it is a wise idea to change them
or leave well enough alone?

Thanks, Tony

7 Answers


I think spark plugs would the be least of your worries on a long trip, make sure your trans fluid, engine oil, and coolant are all at the proper levels. Then I would inspect your tires and brakes, and check your rear differential fluid can do this by taking the check plug out should just have to use a 3/8 ratchet stick your pinky finger in it and point it down as much as you can if you don't have fluid on your finger or you can use an Allen but your rear end is going to take most of the burden while hauling a boat or anything.


Sorry you that last part wasn't quite clear if you don't have fluid touching your finger or the Allen whichever you choose you need to add diff fluid check what your truck takes but most of the time it's 80-90 weight gear fluid pump enough in until it trickles out the check hole and then reinstall the check plug.


Hi Mark, yes I have done all the above already. Its just been a long time since plugs were done, & we know what a pain they are to replace!!!!!!


If you used double platinum plugs they are good for 100k miles.


BTW - I am pretty sure the differential oil is 75W-140 synthetic. It is for my Fords.


Haha yes they definitely are, but most spark plugs last 50k and can go longer just pull the easiest one to get to out and check to see if it's saturated or has a lot of carbon build up and if the tip (where the spark is made from) is not as pointed as it once was, if it seems to be of ok condition but your still concerned, but your self a can of sea foam put half in the gas tank and the other half mixed in your oil, if you know what a drip can is I recommend using that, it's a metal canister that has a cap on top with a hook you hang from your hood latch an it has a hose on the bottom with a gauge on the canister itself, pull your brake booster hose from the booster and put the hose from drip tank into that start your car and run it at around three grand, this will clean out your entire intake system smoke will pour out your exhaust this is normal and the more the worse it was it will smell like a hot egg, but that is a task if you don't really know what your doing, so generally people just do half has and half oil.


The reason I say that is Ford calls out double platinum plugs for the Triton engines. With the right tools they are not that hard to change. If I were going on a trip I would take an extra coil or two and the tools to change them.

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