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Old 11-13-2010, 02:14 PM
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Cooling Indication

Where can I find a detailed wire diagram of the for the cooling system on a 1988 k3500 454tbi. Replaced both temp indicator sensors above ex manifold. replaced temp sensor by thermistat. Replaced whole cooling system, Rad/Pump/Therm/Hoses. The eng temp is normal by feel. hot H20 on top hose, cool H20 on bottom hose. Indications run at 240 Plus, after shut down, gage will peg out. I suspect I have a bad wire. But the real problem is it runs rough at idle, as if it was telling the MAP sensor the eng is hot. I replaced the map sensor. When I pull off the temp sensor off the drivers side manifold it shows O on the gage, this wire seems to ground out, its not the sensor, tested that. Any input on this????????????

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Old 11-13-2010, 03:28 PM
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A big block running that warm should be spark knocking or detonating, is it?
Also you need to be sure that the temp is reading correctly so you will need to check the coolant temp against what the gauge is reading.I use an infrared thermometer with lazer pointer.Makes it pretty simple.just point it at the thermostat housing where the hot water comes out when it is hot, and compare to gauge to be sure of its accuracy.
Need to be sure of engine temp as gauge could be wrong.dont wanna fry your engine either .
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Old 11-13-2010, 10:46 PM
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Thats a great Idea, Never thought of that, I have one at work i can use, I''ll let you know Wednesday if it works. thanks
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Old 11-17-2010, 01:53 PM
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Heads are hot

Use the inferred Thermometer, all indications ck normal, I found the heads are around 270 plus, the temp senors are located right above the exhaust manafold, and they read at 375. Do I have a problem with the heads? I had new guides put in and cleaned up, they looked really good when I installed them. Or could it be I need to readjust the valves? If the valves are not closing all the way, could this be the problem?
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Old 11-17-2010, 03:51 PM
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My guess is you have the wrong head gaskets. When you replaced the heads after the valve guide job you may have installed the wrong head gasket and now the water is not flowing through the heads.

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Old 11-17-2010, 05:27 PM
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You will never get an accurate reading above the exhaust manifold. You should get a meat thermometer and stick it in the radiator while running. Be careful because it is it truly running that hot it will boil over without pressure on it.
Grounds are real important to the system. Once you prove the water temperature is lower than what the gauge reads, I would look for a ground issue.
The other thing is if you have access to a scan tool see what the computer thinks the temp is.
In a truck that old you need to suspect wiring and the most common wiring issue is failed or disconnected grounds and the bad thing is they dont always show up right away
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Old 11-17-2010, 05:40 PM
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Quote:
Originally Posted by vicrod
My guess is you have the wrong head gaskets. When you replaced the heads after the valve guide job you may have installed the wrong head gasket and now the water is not flowing through the heads.

vicrod
,
No I got the expensive gaskets and put them on the right way, I believe my antifreeze was too concentrated, but my timing may be off a bit. I'm going to retime it next week. I'll let you know how it goes. Thanks for the reply. Paul
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Old 11-17-2010, 05:49 PM
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Quote:
Originally Posted by T-bucket23
You will never get an accurate reading above the exhaust manifold. You should get a meat thermometer and stick it in the radiator while running. Be careful because it is it truly running that hot it will boil over without pressure on it.
Grounds are real important to the system. Once you prove the water temperature is lower than what the gauge reads, I would look for a ground issue.
The other thing is if you have access to a scan tool see what the computer thinks the temp is.
In a truck that old you need to suspect wiring and the most common wiring issue is failed or disconnected grounds and the bad thing is they dont always show up right away
Ya, I believe I may have a ground problem too. I had one sensor reading higher than the head so I may have a bad sensor. But the temp switch by the thermostat housing is accurate, is this the only switch that runs the computer,what tells the computer to adjust the Idle when the engine gets hot? Thanks for your help.
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