cooling system issue

[sgull]

My brother was telling me about this cooling system issue he's having with his '97 Ford F150.

"It only happens when it's warming up from sitting overnight. It's strange. It starts to warm up normally, heater starts blowing warm air, then all of the sudden the heater blows cold air and the temp. needle drops way down. Then, when I get on the highway, the needle will spike all the way up to hot (pegs the top of the meter), so I usually pull over, the needle goes back down to normal, and then it's fine from then on."

He says he took it into a good reputable shop where they replaced the thermostat and did a backflush of the cooling system, but none of that helped.

Any comment/ideas what might be a likely cause of the issue as he describes? Thanks.

 

[Road Angels]

heat

Does he have electric fans on the truck?? If so Start there, also how old are the hoses maybe he has a main or bypass hose that has the inner core sucking open and closed, did you pop the hood to see if the engine was over heated and not just showing hot on the gauge,

 

[sgull]

Does he have electric fans on the truck?? If so Start there, also how old are the hoses maybe he has a main or bypass hose that has the inner core sucking open and closed, did you pop the hood to see if the engine was over heated and not just showing hot on the gauge,

He has a regular clutch fan, he says, and the mechanic told him it checks out just fine. He also said he "did smell coolant coming from under the hood, and saw what looked like coolant spray around the overflow bucket. But the needle spiked so fast, like in 2 seconds from normal to pegged."

As far as the hoses, yes they are probably old. Inner cores of old hoses can do like you mentioned, and maybe cause the problems as he's described, that's not unusual?

 

[arizonadirtslinger]

With motor off obviously try so spin fan both ways if there is resistance fan clutch is good if no resistance fan clutch is bad the fan clutch is one of the cheapest fixes on the cooling system and is overlooked a lot I have overlooked it myself and when I figured it out I had to facepalm I had the same symptoms