Mike1968

Recently my Ranger has started running warm at highway speeds. The truck runs fine around town usually running the heater on full is enough to make the temperature gauge creep back down. I know this is not just a simple sensor/guage issue since one time I kept running the truck as it heated up and when I stopped I smelled antifreeze and could hear the boiling when I shut the engine off. The radiator is free of obstructions and the heater blows hot air constantly. Also, when a garden hose is stuck in the open radiator cap the truck does suck in more water when the engine is revved.
My first bet was to replace the thermostat. This did not help the issue so I cleaned the coolant system out for a second time this year (I do this yearly). Still no difference. My third thought was that one of the radiator hoses was collapsing at high engine RPM's so I replaced both of these. The truck runs great around town but just when run at high RPM's it heats up and with summer closing fast this issue will get worse. Also, I work in about 70-80 miles away from where I live so I need to do a lot of highway travelling.
My ranger is a 1993 with the 4.0L engine and has about 150,000 well maintained miles on it. Thank you for any idea's & thoughts you can offer.

LunaticSVT

What it MAY be is your head gasket. If you blew the gasket, hot exhaust fumes can get into the water jackets, which forces the coolant back and make the engine much hotter. It would make the coolant level higher because its getting pushed back. To check to see if the head gaskets are leaking, buy a strip of lime paper at your hardware store. When placed in coolant, it will turn color to indicate if exhaust residue is in the coolant, that gives you a definate answer on the head gasket.

Mike1968

What is lime paper? I imagine it is like litmus paper checking for acidity? Any chance this would show up on a compression test? I do have a tester in the garage and there is plenty of room to get into all six cylinders on this vehicle. Would this also cause the coolant to smell like exhaust?

LunaticSVT

Yes the coolant would have a distinct smell of exhaust. And yes it is pH paper.

You can determine the location of the leak by compression tests. of course you can connect a vacuum gauge to the intake manifold. With the engine Idling, the vacuum gauge pointer will drop sharply, every time the leak occurs. The drop will be from the steady reading shown by the pointer to a reading of 8" to 12" Hg or less. If the leak Is between two cylinders, the drop will be far greater.

drof

Hi, I wouldn't hurt to take a look at the head on the drivers side, The earlier 4.0s would crack, antifreeze can possibly be seen if the valve cover is taken off, it appears as a white , possibly green muck, mixed with the oil somewhere near the back of the head, if its a big one sometimes the leak can be seen without taking off the valve cover. Theres also a part number around that area as well on the head, check with your ford dealer to see it their the older heads.
Its just worth a look, wouldnt want you to do heads twice.