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Vehicle is overheating


villins3
10-06-2002, 11:05 PM
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
07-18-2003, 10:48 PM
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
07-19-2003, 01:24 AM
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
07-21-2003, 03:15 PM
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
08-24-2003, 05:33 PM
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. :confused:

Robert

eagle12
05-24-2004, 06:45 PM
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
05-25-2004, 06:08 PM
just take ur thermostat out and let it run wide open all the itme.....that will keep it from over heatin

eagle12
05-25-2004, 06:46 PM
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
05-26-2004, 10:21 AM
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
05-26-2004, 06:04 PM
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
05-27-2004, 09:21 AM
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
05-27-2004, 09:42 AM
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
05-28-2004, 11:53 PM
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
05-29-2004, 12:23 PM
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
05-29-2004, 10:04 PM
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.

Thunderbolt
05-30-2004, 11:37 AM
I realize the thermostat is set to control the engine temp, But that only controls the max temp the engine will get without the stat opening. If the fan is cooling the radiator faster than it needs to, when the stat opens the engine temps drops more than it needs to until the coolant in the engine warms back up. I have experienced it a few times. I am not saying a flex fan can't be used just that it wouldn't be my choice. The flex fan also robs power since it is on all the time. If it does not work properly with what came on the truck something isn't working properly. The size of the radiator, size and function of the fan, water pump ,radiator cap and the ratio of the antifreeze all play their roll in the engine temp and if any one has a problem the system will not function properly.

Doug Rodrigues
05-30-2004, 11:49 AM
Well, if you're worried about these issues, just replace anything defective with stock components. That should put your mind at rest. But I should mention that after I installed my flexi-fan, my engine didn't run one bit different temperature wise, nor did the fuel consumption change. The fan was noiser, but for me personally I had the peace of mind knowing that no fan clutch was going to go bad again at the wrong place at the wrong time. It's just my personal opinion.

**But while we're on the subject of over-cooling: Would it be accurate to say the in sub-freezing weather as in 10 degrees below zero, would a stock fan with the stock fan clutch over-cool the radiator? What effect would it have on the engine? Think about it. The thermostat isn't there to open at it's maximum temperature, it's there to raise the engine temperature to normal operating temperature at which the thermostat is rated for. For example, a 195 degree thermostat will keep the engine very close to 195 degrees. It's not a maximum temperature....it's the normal operating temperature.

Thunderbolt
05-30-2004, 07:17 PM
Doug, I am not trying to argue because I believe you have a valid point. What your last reply said about the stat is exactly what I meant I just didn't word it right. It actually does control the max temp which is what the operating temp is. If you have a 160 thermostat in there under normal circumstances it will run around 160 and lokewise with any other temp stat. Does this mean the engine can't get hotter ? Absolutly not ! The stat starts to open as the temp approached 160 or whatever temp stat you have and is fully open by the time it reaces that temp. All things being normal that temp is what the engine will run at. Change coolant ratio, or have a bad fan or a restriction to flow and the engine will rise above the stats temp. I have had several trucks through the years that I tried flex fans on and some of them just didn't seem to like them.. Will it hurt anything ? probably not. I never said anything about fuel mileage. I do know that the optimum operating temp for the 88 and up chevy trucks is 195 and this is where they are designed to run. I have never had a clutch fan just up and konk out on me and I check mine often and when they spin to freely or get play in them I replace them with a heavy duty one. I know flex fans are good,But there is nothing wrong with clutch fans and my whole point of my first reply was to get that point across. If the clutch is bad replace it is all I am saying. If the clutch fan worked for as long as it did why change it ?? My fan on my truck moves just as much air as a flex fan if not more and I don't have to listen to it all the time. My 92 had 180,000 miles on before the fan acted up, But it never overheated. I put a hevy duty clutch on and 45,000 later it still works. My 98 is on 175,000 and the fan still works great. All I was trying to say is if a vehicle works for 70,000 miles with certain components and one finally needs replacing why change it to a different type when the ones that were on there worked that long ?? Also if a clutch fan is suspect in overheating and it is replaced, But the vechicle still runs hot so you put a flex fan on and it runs a little cooler you still haven't fixed the problem and something else isn't functioning properly.

Doug Rodrigues
05-30-2004, 07:47 PM
But that's my point...putting on a solid fan won't make it run any cooler. The thermostat will still maintain the engine temperature to it's designed temperature. Next to no circulation will occur if the thermostat remains closed. The thermostat forces the engine to rise to it's designed temperature. If the temperature goes higher than the thermostat's designed temperature, then the thermostat is stuck closed, or there is crud in the radiator which prevents adequate heat exchange, or there is no liquid in the radiator. Radiators which have mineral deposits don't dissipate heat fast enough. They'll work okay in cold weather, but when hot weather arrives the engine overheats.....a good reason to use distilled water with the anti-freeze instead of tap water. Maybe my postings are just adding to the confusion....but I'm not confused. :iceslolan

Thunderbolt
05-31-2004, 02:12 AM
I see what you mean and I agree.

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