1988 S-10 4.3L "Z" with a new motor 20K or so ago. Also got new waterpump,
thermostat and both temp gauges at that time.
A week ago I got the oil changed. On the drive home, I notices my temp guage
registering an uncomfortably high level (265 is the top line, it was at that
top line). No boiling over at all or anything, but I threw on the heater on
high and got home quick. I have now replace the thermostat (which appeared
to be fine) with a 195F as is called for. I also put a new radiator cap on.
I have been driving it all week now, and what I am seeing now is after 2 or
so miles, the temp gauge will register 265F for 10-15 seconds, and then will
quickly drop down 210ish (where it always ran prior to these issues) over
the next 30 or seconds of operation. This can occur whether at a stop light
or driving down the hiway. Again, never has it boiled over, no change in
coolant level, no leaks etc.
So I am curious if my gauge or sensor is FUBAR, or if something worse is
going on. I have purchased a mechanical gauge to put in it to see what the
temp actually is running. I wanted to see if anyone has any
ideas/suggestions, and I also wanted to verify that the dash temp gauge is
the one that is in the side of the block and NOT the one on top of the motor
near the thermostat. Right? I obviously don't want to do the work twice, and
I know if I pull the computer's temp sensor my truck will run like a dog.
Generally GM motors that need to have the air bled from the cooling system
have one or two ports at the top of the motor some where. I'm not familiar
enough with the 4.3 to know if it has them. Some of them are at the top side
of the intake I think. Generally you would remove the plug from the bleeding
port while it's running and warmed up and wait for coolant to come out with
I am not aware of any such port on my 89 4.3. I basically have the same
truck he does.
I'd check and make sure you got the proper rotation of waterpump-- they make
a standard and reverse.
Check for leaking head gaskets. Water in oil/oil in water?
Installing the Tstat backwards, perhaps?
by all means plumb in the mechanical temp gauge and see what it tells you. I
would NOT attach it inside the vehicle-- unless you like the idea of trying
to control the vehicle as scalding hot water sprays all over you.
How old is the radiator? Might want to have it inspected--- some time with a
temp gun might show you you have a lot of blocked-off cores.
Kinda in a hurry, but had a similar problem with my 89 a while back, that I
fixed. Don't mind helping out if you give me the above info and do the
Correct rotation of waterpump. Waterpump has worked fine for 20K, and
appears to be working fine still (no weaping, circulation visible with
radiator cap off).
No water in oil, no oil in water.
Previous Tstat was installed correctly, and worked just fine for 20K. New
Tstat put in exactly as old one was taken out. The only thing that is
different is that the old Tstat (which was taken out after the beginning of
these problems) seemed at visual inspection to flow more freely than the new
Tstat. That is just my eyeballing it and seeing how much space is made when
it opens though, no real evidence that the new one is flowing
Radiator is original, though it has been flushed at least twice by me (twice
in the past 45K, once on old motor, once on new motor). There are a few
dinged fins, but nothing to really reduce airflow. I've run my hand over
the radiator (front and back) after bringing motor up to temp, and it
appears to be getting evenly hot, though a core may be plugged in spite of
that. I'll have to check around and see if I can find someone with a thermo
gun. Fun to play with for those of you who haven't used one.
Any help is appreciated. This is one of those weird ones, and the idea of
melting down my motor is not appealing :-)
You can easily check and see if you have an "air in the system"
problem on your truck. Check the level of the coolant in the
radiator "cold"..ie: after it has sat overnight, and before you
start her in the morning. If it's low, top it up, and make sure
that you have the level in the overflow bottle to at least the
"cold" level. It does not hurt anything to run the overflow
bottle a little higher.
Now go drive the vehicle, let it warm up...then let it sit
until it cycles again. Where is the level in the rad? If you
have a properly working rad cap, a cooling system with
no leaks, and no restriction from the radiator to the
overflow bottle, it should be full. If not, you will need to
investigate those areas a bit more.
4.3's in the s/t trucks don't have bleed screws. If I'm filling
one after the block has been completely emptied...I find
it much easier to just remove the heater hose that goes into
the intake manifold. When you get coolant coming out of
that point as you are filling the radiator, you will pretty much
have all the air out. You can then run the engine with the
rad cap off, allowing the level in the rad to be a bit low (2-3")
until the vehicle hits t/stat opening temp. Once you have
coolant flow through the radiator, air will automatically be
purged, and you can just top up the rad while she is running.
Anyway, hopefully you can eliminate air in the system as
your cause and move on to other diagnostic areas.
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