As the thread title states, I have a 97 K2500 Suburban, 122K miles with a 454 Vortec that's overheating. I've done a bunch of work to it over the past few months and before I pull the heads I want to see if I'm possibly overlooking another problem causing the overheating. Here's a summary of issues and work I've done to the truck.
The truck came from my brother, he was moving across the country and he made it about 30 miles before the truck started to overheat. It was losing a lot of coolant, he didn't know why so he topped it off a couple times and eventually made it back home. A few weeks later I went to pick the truck up and found it low on fluid and found the culprit, broken heater hose fitting for the rear heat. I capped it off, topped off the fluid and made the 8 mile drive home with no issues.
Since I had the system open for the heater hoses and fittings, I decided to replace the water pump, thermostat, upper/lower radiator hoses and the fan clutch. After I finished installing all those parts I found the operating temp would sit at 225 and quickly jump to 240+ if I drove it or held the rpm at 1500+ rpms while stationary. I also found a small leak on the radiator so I ordered a spectra replacement radiator and installed that.
The same overheating issue continued with a new radiator and I noticed the truck was running a little rough and smoking out the tail pipe a little. Based on the smokle I started to think maybe it had a head gasket failure so I pulled the plugs. I found the plugs on the drivers bank were normal and the passenger bank were black, rich as hell (none of the plugs showed signs of coolant). Some quick research told me the culprit was likely the upper O2 on that bank so I bought all 4 Denso O2's and replaced the uppers on both banks and installed new AC Delco plugs. The truck ran a lot better, no more smoke however the overheating condition continued.
Pic of the plugs and upper O2's
I decided to connect my Autel Scanner for some live data and noticed my CTS for the ECU was showing 185-195 while the temp sensor in the head for the gauge was showing 225+ (via the dash gauge). I started to wonder if the truck was really overheating or possibly a sensor was failing so I replaced both temp sensors with AC Delco parts. Once again, those parts didn't make a difference.
I started to wonder if I had air in the system or possibly the thermostat was sticking so I swapped out the thermostat for a 195 degree Stant (drilled two 1/8" holes in it) and bought a OEM tools funnel kit so I could properly bleed all the air out. I also pressure tested the coolant system and confirmed it held pressure as it should. No changes......
I haven't touched it for a month until this morning when I noticed a dab of weird milky crap under the oil cap and the oil level was high. I've seen a milky cap before but never a small amount like this and the color is usually lighter.
Now I'm back on the head gasket or cracked head possibility so I pulled all the plugs and dropped the oil. Plugs looked great, no sign of coolant and the oil looked very watery so I put it a clear plastic bin so I could see coolant separate, assuming it had some mixed in. I still can't smell worth a shit so I had a friend confirm it smells like gas, really strong gas. No separation was found in the oil and no sign of coolant after several hours. I can only assume it was running rich enough on the passenger bank that the oil was washed out with fuel. I replaced the oil filter and put new oil in the engine and while I was at the store I picked up a coolant testing tool so I could see if exhaust can be found in the coolant. That test came back negative.
At this point I'm not sure if it's a HG issue or some sort of cooling issue? The fact the truck drove home from my brothers house without overheating and all the problems started AFTER I replaced the entire cooling system, makes me question it being a HG or cracked head. I also keep wondering why there's a large difference in the temp readings between the head and the intake manifold.
I'm all ears for any ideas you guys might have.
pic of the truck
The truck came from my brother, he was moving across the country and he made it about 30 miles before the truck started to overheat. It was losing a lot of coolant, he didn't know why so he topped it off a couple times and eventually made it back home. A few weeks later I went to pick the truck up and found it low on fluid and found the culprit, broken heater hose fitting for the rear heat. I capped it off, topped off the fluid and made the 8 mile drive home with no issues.
Since I had the system open for the heater hoses and fittings, I decided to replace the water pump, thermostat, upper/lower radiator hoses and the fan clutch. After I finished installing all those parts I found the operating temp would sit at 225 and quickly jump to 240+ if I drove it or held the rpm at 1500+ rpms while stationary. I also found a small leak on the radiator so I ordered a spectra replacement radiator and installed that.
The same overheating issue continued with a new radiator and I noticed the truck was running a little rough and smoking out the tail pipe a little. Based on the smokle I started to think maybe it had a head gasket failure so I pulled the plugs. I found the plugs on the drivers bank were normal and the passenger bank were black, rich as hell (none of the plugs showed signs of coolant). Some quick research told me the culprit was likely the upper O2 on that bank so I bought all 4 Denso O2's and replaced the uppers on both banks and installed new AC Delco plugs. The truck ran a lot better, no more smoke however the overheating condition continued.
Pic of the plugs and upper O2's
I decided to connect my Autel Scanner for some live data and noticed my CTS for the ECU was showing 185-195 while the temp sensor in the head for the gauge was showing 225+ (via the dash gauge). I started to wonder if the truck was really overheating or possibly a sensor was failing so I replaced both temp sensors with AC Delco parts. Once again, those parts didn't make a difference.
I started to wonder if I had air in the system or possibly the thermostat was sticking so I swapped out the thermostat for a 195 degree Stant (drilled two 1/8" holes in it) and bought a OEM tools funnel kit so I could properly bleed all the air out. I also pressure tested the coolant system and confirmed it held pressure as it should. No changes......
I haven't touched it for a month until this morning when I noticed a dab of weird milky crap under the oil cap and the oil level was high. I've seen a milky cap before but never a small amount like this and the color is usually lighter.
Now I'm back on the head gasket or cracked head possibility so I pulled all the plugs and dropped the oil. Plugs looked great, no sign of coolant and the oil looked very watery so I put it a clear plastic bin so I could see coolant separate, assuming it had some mixed in. I still can't smell worth a shit so I had a friend confirm it smells like gas, really strong gas. No separation was found in the oil and no sign of coolant after several hours. I can only assume it was running rich enough on the passenger bank that the oil was washed out with fuel. I replaced the oil filter and put new oil in the engine and while I was at the store I picked up a coolant testing tool so I could see if exhaust can be found in the coolant. That test came back negative.
At this point I'm not sure if it's a HG issue or some sort of cooling issue? The fact the truck drove home from my brothers house without overheating and all the problems started AFTER I replaced the entire cooling system, makes me question it being a HG or cracked head. I also keep wondering why there's a large difference in the temp readings between the head and the intake manifold.
I'm all ears for any ideas you guys might have.
pic of the truck
