When you're doing the service one of the most important overlooked parts is the inspection.When you think service you think oil and filters but there's much more that goes with it. When you're doing the inspection get handsy touch feel push, pull, move all pipes and hoses whatever you can get your hands on. This will kind of give the condition that the truck will experience when driving down the road with vibration and movement. You're better off finding the problem now rather than a thousand km's down the road or even 200 km's down the road when this vibration or movement causes a problem. Imagine the customers thoughts when they do their first trip after you've serviced it and something silly like a hose leaks or something blows. It might not have been leaking at the time when it was in the workshop but the customer's thoughts are "I just had this thing in for a service and it's broken down."
Inspect your belt- as a general rule you want to be able to deflect the belt the width of the belt. The greater your distance between your pulleys, the greater the deflection is going to be. Have a look at the belt for cracks and general wear and tear. Take notice if you're driving the truck even if thats just into the shed. Give it a couple of revs see if it is squeaking.
Inspect your exhaust manifold gaskets for any signs of leaking. Black soot is the tell-tale sign. Check your oil level make sure you've given the oil time to drain down to the sump. check your coolant level.
Check your hoses you're looking for rub marks. When looking at the rub marks you want to look to see how far it's rubbed through and make the call if the pipe is still serviceable. Look for any signs of leaking if you find a spot where it has been rubbing put a piece of rubber in between it and zip tie in place. Check the clamps make sure that they're not loose.
Check your radiator for leaks. Also check to see if it is clogged and blocked with dirt and bugs especially if you're running in hot weather. Check your power-steering oil level. Checking your intake pipe from the air cleaner is extremely important in dusty conditions make sure your clamps are tight and there's no holes rubbed through the hose. Nothing wears out your engine quicker than sucking dirty air. Don't forget your air lines on the firewall give them a wiggle and make sure nothing's leaking or rubbing.
One thing I didn't get any footage on was the fan hub you want to get in there grab hold of the hub give it a wiggle see if you can get any movement out of it the fan hub should have very little movement.