Vehicle is overheating

[villins3]

I have a 94 Chevy pickup 2500 series, 5.7/AC/Automatic. It has been consistenlty overheating for the last month. It has only been the last week or so, where it is actually starting to boil over. I have replaced the radiator, radiator cap, top and bottom hoses, thermostat (3 times), ECT sensor, flushed the system (twice) & water pump. I am not sure where to go next. I have taken it to a Chevy dealer and they cannot figure it out.

Any help would be greatly appreciated!!!!!

[rosebush]

Have u checked the water pump.Push on the hoses to make sure its working.Otherwise all i can think of is a weak head gasket.

[Shortbus]

Boiling over sounds like the Antifreeze mixture is to lean. Or system pressure is to low. Did the dealership check to see if your truck is running to lean of an Air/Fuel Mixture. Since you replaced all of the other critical items, that is the only thing I can think of.

A lean burn will produce a lot more heat and make the engine work harder.

Also did they check your fan and clutch for proper operation? These also greatly impact cooling performance.

Once last thought check for a restricted coolant nipple at the back of the intake. It is the screw in quick disconnect fitting, they have a plastic insert in them that can dislodge and cause problems.

[dracer398]

Here is something else to check, make sure that your lower radiator hose isn't collapsing. I see you changed yours but I would still check. It happened to me on my 1996 7.4. The only way I found it was after I replaced the hose I cut the old one open and could see the marks where the hose collapsed. The hose was the factory hose which had the corrugated plastic around the outside which made it hard to see.

[Rob_0126]

Originally Posted by John

Boiling over sounds like the Antifreeze mixture is to lean. Or system pressure is to low. Did the dealership check to see if your truck is running to lean of an Air/Fuel Mixture. Since you replaced all of the other critical items, that is the only thing I can think of.

A lean burn will produce a lot more heat and make the engine work harder.

Also did they check your fan and clutch for proper operation? These also greatly impact cooling performance.

Once last thought check for a restricted coolant nipple at the back of the intake. It is the screw in quick disconnect fitting, they have a plastic insert in them that can dislodge and cause problems.

If it's running lean, it could be the o2 sensor. I believe a bad o2 sensor causes a rich condition, but I could be wrong.

Robert

[eagle12]

Try removing the seal around the thermostat if you have one and let it float in the housing which will allow proper seepage to occur. You will , of course, have to use a gasket or rtv at the housing instead of the 'internal' seal at the thermostat.

[wehswarriorS-10]

just take ur thermostat out and let it run wide open all the itme.....that will keep it from over heatin

[eagle12]

Yes, but your computer will run as if the engine was cool all the time and run rich and your gas mileage drops and improper combustion will foul engine components. Engines run better and smarter when at the designed hot temperature.

[Thunderbolt]

Eagle12, I would just drill a hole in the thermostat instead of not using the rubber seal. I think in one of your other posts you may have done that and I think the seal makes it much easier to change the thermostat than using a gasket.By drilling a hole you can experiment starting with one smaller hole working to a larger or more smaller holes. If he hasn't replaced his fan cluth I would also put a new heavy duty one on. These trucks are very touchy when the clutch on the fan isn't working properly.

[eagle12]

Yes, that is what I've done, except for a 1/8" hole and judging by the warmup and all data I do need another 1/8" hole on the opposite side of the flange. I know my fan clutch is working because before I did the 'hole' thing my engine would heat up to near dangerous levels and when the cold pocket of water finall got hot and hit, BAM!! -very quick cool down and stayed there. Which tells me cooling fan is cooling. Now it works fine and I keep my easy -to- change seal!! Hope it solves other peoples' problems. Much appreciation and May God be with you all.

[gmsmallblockguy]

Did any of the parts you changed out have white gell like deposits in them? Just one thing I didn't see mentioned. If dexcool and green coolant ever got mixed in there it can gell and clog up everything. Even after standard flushing it will still be in there. To get it out you need an ACID flush.

[broughy84]

This is also something that I did not see mentioned.

Did you check your fam clutch? My truck would overheat everytime I drove it, I replaced everything, (the radiator leaked anyway) still couldn't figure it out. Still did it. My father in law asked about the fan, had I checked it? NO, I totally forgot about it. It was to LOOSE and was not spinning properly to get enough cooling power. Changed it, never overheated since.

[Doug Rodrigues]

I think that Broughy84 has given you the most logical advice and the probable cause of your problem. Fan clutches go bad more often than anything else. On my old CK, I got rid of it completely and installed a Flexi Fan.

[Thunderbolt]

Originally Posted by Doug Rodrigues

I think that Broughy84 has given you the most logical advice and the probable cause of your problem. Fan clutches go bad more often than anything else. On my old CK, I got rid of it completely and installed a Flexi Fan.

As I said in my earlier post The fan clutch would be my guess. However I would not install a flex fan I would install a heavy duty clutch. You would probably get away with it, But the problem with clutch fans is they can sometimes cause overcooling. The electronics are designed for the engine to run in a certain temp range and if it runs to cool it causes a whole new set of problems because the computer thinks the engine isn't up to operating temp.

[Doug Rodrigues]

Assuming that the fan clutch is functional , the thermostat is what controls the temperature of the engine. Once the engine heats up, only then can hot coolant be pumped into the top radiator hose. When the radiator becomes hot enough to affect the fan clutch thermostat, only then would the fan clutch engage the fan to pull cooling air through the radiator fins. The thermostat inside the upper radiator hose connection at the intake manifold is what controls the engine temperature...nothing else. The only way that the engine would run too cold is if someone drilled holes in the thermostat, removed the thermostat, OR the thermostat became defective. However, a defective thermostat usually remains in the closed position and would normally cause overheating. Since the thermostat has already been replace, it would be safe to rule-out a defective thermostat. However, if you want to go further and check the operation of the thermostat, just drop it into a pan of water and heat the water until the thermostat opens. A cooking thermometer would be nice to use. Don't get it any hotter than what was necessary to cause it to open, because excessive heat will ruin the thermostat! That's what normally ruins thermostats....an engine blows steam because of a leak and the thermostat also gets ruined at that time too.