engine overheating on 2004 Ford Freestar

my temperture gauge on my van reads normal when driving at 50-50 mph and then when i speed up 60-65 it goes up to about 3/4 of the temp gauge. i have changed radiator and thermastat but to no avail it still appears to be getting hot. funny thing it does not do this all the time. i can go days without it acting up. also when it is [overtemping] according to the gauge we have check the resevoir and it is not boiling as it should be. according to my mechnic the temp sensor are reading at abouit 230 degre's at high idle. could it be a false reading and if so whats temp sensors could we check

by in Rosenberg, TX on December 22, 2010
3 answers 4 comments
ANSWER by on December 22, 2010
did you replace the rad with a new unit?? it sounds like a circulation problem. I would also look at the water pump impeller. may be rotted out or loose on the shaft. Roy
COMMENT by on December 22, 2010
is there any firm way to tell if it is the waterpump. its about 300 to 350 to replace
COMMENT by on December 22, 2010
if there is a small hose at the top of the plastic tank, remove it and aim it to a bucket. start the motor and see if fluid is coming out at a good rate. my guess is that it may be just above a dribble. otherwise, you have to remove to confirm. Roy
ANSWER by on December 22, 2010
I'm thinking it could be a false reading from the temperature sending unit. 230 degrees is quite hot for a vehicle going down the highway with maximum air flow. As Roy implied - is the radiator you replaced the like-kind OEM style or used or aftermarket? You do not want this engine overheating by the way...even with new style gaskets, the 3.9L (formerly 3.8L) V6 is succeptable to head gasket failure.
COMMENT by on December 23, 2010
i have replaced the Rad once about 15 months ago and then again [because it was leaking] about 3-4 months ago. we did use OEM style. funny thing about the overtemping is that this happen about 15 months ago which did not fix the problem. we did replace thermastate which did fix it. but now it is doing the same thing. sometimes it gets hot sometimes not. like i said before even at that tempature it does not seem to be boiling water in the resevoir which it should. is there any way to actually measure the water temp and still keep the system closed and sealed up.
COMMENT by on December 24, 2010
The only thing you can really do is replace the sending unit and check it that way. Or, a temperature sensor gun that you aim at things and measures temperature can get you close. Don't be too sure the coolant should boil, not necessarily.
ANSWER by on April 09, 2015
My wife's van did this also. It is a bad head gasket that is causing the exhaust to flow into the coolant system. It's caused by the pressure that builds the faster you go. Get it checked out before you crack a head.
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