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38 Posts
Truck is stock w/ ~175,000 miles on the odometer. Original owner.
It started with a leaky water pump. Water pump went quickly. Dumped about half of the coolant on a 10 mile round trip. For my initial diagnosis, I added a gallon of distilled H2O to the degas bottle. (Engine not running.) I could hear water hitting the ground before I got the full gallon in there. Water pump was dumping it. Easiest leak detection ever.
All testing below has been done with ambient temp between 50° and 65°F.
Replaced water pump, (new water pump has the curved connector to lower rad hose, original had straight - replacement lower hose is correct for the curved connector) t'stat and gasket, upper an lower rad hoses, and coolant temp sensor. Refilled. Checked for leaks. All good. Fire up engine and idle for about 10 minutes before temp guage starts climbing. Eventually showing max hot.
Shut it down. Rad hoses cold. Heater not blowing hot. Just hot on the guage.
Continued investigating. Pulled t'stat and bench tested (stovetop). It would open ~3/8" between 190° and 210°F. (192°F spec t'stat).
Replaced t'stat with another new one.
Refill system. Run again. Same results.
Decided I must have air trapped in system. Tried filling the system through the t'stat housing before installing t'stat and upper rad hose. Same results.
Tried vacuum filling the system (at a stable 26 inches of vacuum - indicating no leaks).
Same result.
Now getting suspicious that the new water pump is a complete dud. Hot on the sensor but cold hoses suggest no flow to the radiator.
Did a "modified-Gooch" coolant flush. Flushed radiator separately with garden hose followed by distiled water. Pulled block plugs and drained block. Installed a gutted t'stat. (Essentially NOT a t'stat. just a shim to hold the t'stat gasket in place to prevent leaks.) Refilled system with distilled water (gravity fill not vacuum) to continue the flushing. Crank it up and let it idle with intermittent revving to ~2000 rpm and heater set on high.
All was good for about 15 minutes. Temp guage stayed right in the middle of the scale. Heater air was warm (but not hot). Rad hoses were warm (not hot or very firm). I was feeling good.
Still with the dummy t'stat installed, I took off to drive it a few miles, and within 1/2 mile the temp guage starts to creep up. By the time I can get turned around and back home, the guage is on full hot and the Check Guage light is on. NOT Good.
Then it got weird. Heat was still warm. (Warmer than at idle - but not as warm as I would want on a cold morning). Rad hoses still warm. I drained the radiator, and coolant was warm, but not uncomfortably hot.
I immediately pulled the block plugs and again coolant was warm but not uncomfortably hot. Certainly not hotter than the 192°F setpoint or whatever the top of the guage should be. (250°+ F ???) If that water had been at 250°F, I would have been headed to the hospital. Warm coolant in the radiator is telling me that the pump is pumping. That finally seems like some good news.
So... I'm thinking that I have a bad temp sensor - or I have a bad connection to a good temp sensor. I say that because - if the system was truly hot, I should have been burned while draining the block. It's possble that the sensor is good but the connection is bad. Maybe the connection at idle was good but the vibration of driving it 1/2 mile moved it a little and caused a faulty reading. I did put a little dielectric grease on the temp sensor connector when I installed it. Is that causing the faulty reading?
I have it all put back together with a real t'stat now, but I haven't refilled it yet. Is there something else that I could be overlooking here before I really attack the sensor. I'm hesitant to remove the sensor because I'll probably just do more damge to the connector in that process. I'll probably cut the wires to the sensor and remove with the connector attached and then splice the wires for reinstall. The access / visibility to the locking tabs on the connector is pretty limited. I guess that's my fault for not torquing the sensor to end up the with the tabs on the connector facing forward. I don't remember the orientation of the original sensor.
Other possibility - air pocket trapped right at the sensor causing it to read badly??? I'm reaching.
Please help. I want to drive my truck again.
It started with a leaky water pump. Water pump went quickly. Dumped about half of the coolant on a 10 mile round trip. For my initial diagnosis, I added a gallon of distilled H2O to the degas bottle. (Engine not running.) I could hear water hitting the ground before I got the full gallon in there. Water pump was dumping it. Easiest leak detection ever.
All testing below has been done with ambient temp between 50° and 65°F.
Replaced water pump, (new water pump has the curved connector to lower rad hose, original had straight - replacement lower hose is correct for the curved connector) t'stat and gasket, upper an lower rad hoses, and coolant temp sensor. Refilled. Checked for leaks. All good. Fire up engine and idle for about 10 minutes before temp guage starts climbing. Eventually showing max hot.
Shut it down. Rad hoses cold. Heater not blowing hot. Just hot on the guage.
Continued investigating. Pulled t'stat and bench tested (stovetop). It would open ~3/8" between 190° and 210°F. (192°F spec t'stat).
Replaced t'stat with another new one.
Refill system. Run again. Same results.
Decided I must have air trapped in system. Tried filling the system through the t'stat housing before installing t'stat and upper rad hose. Same results.
Tried vacuum filling the system (at a stable 26 inches of vacuum - indicating no leaks).
Same result.
Now getting suspicious that the new water pump is a complete dud. Hot on the sensor but cold hoses suggest no flow to the radiator.
Did a "modified-Gooch" coolant flush. Flushed radiator separately with garden hose followed by distiled water. Pulled block plugs and drained block. Installed a gutted t'stat. (Essentially NOT a t'stat. just a shim to hold the t'stat gasket in place to prevent leaks.) Refilled system with distilled water (gravity fill not vacuum) to continue the flushing. Crank it up and let it idle with intermittent revving to ~2000 rpm and heater set on high.
All was good for about 15 minutes. Temp guage stayed right in the middle of the scale. Heater air was warm (but not hot). Rad hoses were warm (not hot or very firm). I was feeling good.
Still with the dummy t'stat installed, I took off to drive it a few miles, and within 1/2 mile the temp guage starts to creep up. By the time I can get turned around and back home, the guage is on full hot and the Check Guage light is on. NOT Good.
Then it got weird. Heat was still warm. (Warmer than at idle - but not as warm as I would want on a cold morning). Rad hoses still warm. I drained the radiator, and coolant was warm, but not uncomfortably hot.
I immediately pulled the block plugs and again coolant was warm but not uncomfortably hot. Certainly not hotter than the 192°F setpoint or whatever the top of the guage should be. (250°+ F ???) If that water had been at 250°F, I would have been headed to the hospital. Warm coolant in the radiator is telling me that the pump is pumping. That finally seems like some good news.
So... I'm thinking that I have a bad temp sensor - or I have a bad connection to a good temp sensor. I say that because - if the system was truly hot, I should have been burned while draining the block. It's possble that the sensor is good but the connection is bad. Maybe the connection at idle was good but the vibration of driving it 1/2 mile moved it a little and caused a faulty reading. I did put a little dielectric grease on the temp sensor connector when I installed it. Is that causing the faulty reading?
I have it all put back together with a real t'stat now, but I haven't refilled it yet. Is there something else that I could be overlooking here before I really attack the sensor. I'm hesitant to remove the sensor because I'll probably just do more damge to the connector in that process. I'll probably cut the wires to the sensor and remove with the connector attached and then splice the wires for reinstall. The access / visibility to the locking tabs on the connector is pretty limited. I guess that's my fault for not torquing the sensor to end up the with the tabs on the connector facing forward. I don't remember the orientation of the original sensor.
Other possibility - air pocket trapped right at the sensor causing it to read badly??? I'm reaching.
Please help. I want to drive my truck again.
