Hello All,
I am not new to the forum but it has been a really long time. I had to register again.

I am like many of you and I love my 94 4x4 pickup but I have a question. 22RE with 200K or so (No Speedo).

Recently it overheated during normal driving, I replaced the thermostat, flushed out the radiator as best I could with the time I had available. Added new coolant and the truck ran fine for several days.

3 days ago I got a engine check light which turns out to be a code 42 (Speed Sensor) code 71 (EGR Valve). Everything has been running fine as far as performance and so forth until yesterday morning.

Yesterday and today in the morning the temperature gauge slowly moved across into the red area within 10 minutes of driving. I turned the heat on high and the gauge immediately went down to normal. I turned off the heat and no issues at all for the rest of the 45 minute drive in. The radiator does still have some dark brown sludge/paste that is building at the cap but I am thinking this is rust (oil is not milky and looks fine) and I should be able to flush out. Can't imagine this little bit of rust causing this behavior though.

Any ideas as to what could be causing the over heating in the morning?

I am not so worried about the speed sensor error but have not had time to look into the EGR yet.

Thanks in Advance,

Dbow

 

A brand new radiator might fix it. Do this test next time it starts to get too warm....lift hood...feel upper radiator hose(is it pressurized and very hot?)....now feel the lower rad hose (is it cool?)....

if top is hot and bottom cold then the radiator is clogged.

another questionm...does it overheat on the highway?

 

Hi Zuk,

It runs fine on the highway with no issues. I have also noticed that later in the day when it is hotter it does not do this either.

This morning it did the same thing but I did not turn on the heater and the temp went back down on its own. It was just coincidence on the prior days that I turned on the heater and the temp went down.

I am starting to think that maybe the thermostat that I put in was the higher temp thermostat instead of the recommended OEM temp thermostat. The box had the right part number in it but maybe the actual thermostat was the wrong one. I will have to check.

Dbow

 

The OEM thermostat was revised to a two-stage unit due to known temp overshoot issues. Start by replacing whatever thermostat you put in there with OEM.

 

ok....since it runs ok on the highway then we can forget the radiator...but what about the fan clutch?

 

Running hot while sitting still i would suspect fan clutch... Since you already replaced the thermostat... assuming its not a "bad" part.

Running hot during high speed driving i would suspect a blockage..

Possible water pump impeller "fins" "blades" damaged...

Sludge in the cooling system is normally the breakdown of very aged and over used coolant... eventually like oil coolant will start to turn to a solid once all of the additives and detergents are used up.