heat and voltage
12-26-2000, 04:17 PM
#1
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heat and voltage
This is two questions really.. but they're somewhat related.
First off, what are all the things that would cause a car to run hot? I'm not talking about the occasional temperature spike. My car runs between 230 and 240, which is a bit hot for me. Things I can think of are:
Bad belt (just replaced, the other one was about to die -- no change)
Bad timing (just checked, 8*BTDC, doesn't matter where the timing's at though)
Bad computer, doesn't seem too likely, it's not throwing any codes and most everything runs fine.
Bad thermostat
Bad fan switch
Bad temperature gauge (doesn't seem too likely, but always a possibility)
Now, when the fan switches on at 240*, there's a large voltage drop. Or so says the gauge, at least. I expect there to be some drop in voltage every time an electric device comes on, but this seems a bit extreme, as much as 3 volts for the fan. After it's on it'll raise back up to normal (about 12v for my car), but slowly, not nearly as fast as it dropped. It's not just the fan switch either, everything causes a difference. (Which again I know is normal, just this degree of difference makes me concerned.) Blinkers cause at least a 1 volt difference. Parking lights cause about a half a volt difference.
Of course, these differences are estimates as the gauge in the dash doesn't measure that accurately. The voltage will drop wether I'm idling or cruising down the highway at 2000rpm's.
Does this sound like an alternator getting ready to go to that great junkyard in the sky?
------------------
89 iroc-z 305 tbi
everything stock, except for a mirror that fell off
First off, what are all the things that would cause a car to run hot? I'm not talking about the occasional temperature spike. My car runs between 230 and 240, which is a bit hot for me. Things I can think of are:
Bad belt (just replaced, the other one was about to die -- no change)
Bad timing (just checked, 8*BTDC, doesn't matter where the timing's at though)
Bad computer, doesn't seem too likely, it's not throwing any codes and most everything runs fine.
Bad thermostat
Bad fan switch
Bad temperature gauge (doesn't seem too likely, but always a possibility)
Now, when the fan switches on at 240*, there's a large voltage drop. Or so says the gauge, at least. I expect there to be some drop in voltage every time an electric device comes on, but this seems a bit extreme, as much as 3 volts for the fan. After it's on it'll raise back up to normal (about 12v for my car), but slowly, not nearly as fast as it dropped. It's not just the fan switch either, everything causes a difference. (Which again I know is normal, just this degree of difference makes me concerned.) Blinkers cause at least a 1 volt difference. Parking lights cause about a half a volt difference.
Of course, these differences are estimates as the gauge in the dash doesn't measure that accurately. The voltage will drop wether I'm idling or cruising down the highway at 2000rpm's.
Does this sound like an alternator getting ready to go to that great junkyard in the sky?
------------------
89 iroc-z 305 tbi
everything stock, except for a mirror that fell off
12-26-2000, 05:31 PM
#2
Enkil,
I'll take these backwards. First, the electrical problem.
The voltage drop from load current (I/R drop) might not be the alternator. A drop from load at idle is somewhat normal, but at higher RPM the alternator should be able to offset the load. If you want to check alternator absolute output, briefly ground the diagnostic terminal on the back of the alternator. The tab is visible through a "D" shaped hole in the rear of the alternator, next to the regulator mounting pad. With a voltmeter connected to the alternator output, briefly insert a short screwdriver to bypass the regulator and operate the alternator at maximum voltage output. The voltage should jump to over 17VDC, so only do this for a second or so. If the voltage doesn't rise, the alternator may be failing. If the alternator output rises as described, the problem is either with the regulator or connections in the system. Since teh regulators usually fail catastophically, if you are getting any output voltage now, the regulator is probably O.K. Check alternator and engine grounding, the alternator output stud connection, battery connections, both the positive power and ground nodes at the body near the battery. A poor connection at any of these points can cause the symptoms you are describing.
While the dash instruments are not highly accurate, the voltmeter is among the more accurate. Even if it does not show the correct voltage, the relative change in the reading from loads is probably close to accurate.
As far as the overheating, the timing seems reasonable. Make sure the coolant is full and flowing throught the radiator. Remove the radiator cap and start the engine, allowing it to warm up. As the thermostat opens, you should be able to see very active flow in the right radiator tank. As you increase engine speed, the tank level should reduce sharply, then rise. If not, the thermostat may be restrictive or the pump may be worn and not moving coolant adequately, or the lower radiator hose may be collapsing from the pump suction.
Make sure that air can flow freely through the radiator. Check for obstructions and debris buildup in front of the radiator and between it and the air conditioning condenser. Make sure the lower air deflector on the lower radiator support is in position and not damaged.
The fan(s) will not start until the temperature is at or above 220°F on most TPIs, and TBI is likely similar. If your temperature geos way above that with no fan start, the switch or CTS might be suspect.
If the coolant is flowing well and the upper radiator hose is hot from the open thermostat, the next possible problem is scale and corrosion buildup in the radiator and/or block which is not allowing effecient heat transfer. You could try flushing with an acidic cleaner, then neutralize and flush with clear water, but a scaled radiator is very difficult to clean in that manner. The most effective means is a tear-down and recore, rodding out the existing core, or caustic chemical boiling of the radiator. Any of these are typically radiator shop specialty services. A replacement radiator can often be cheaper than a recore service.
A little more detail on the symptoms would be beneficial so that more specific suggestions can be offered.
------------------
Later,
Vader
------------------
"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0
I'll take these backwards. First, the electrical problem.
The voltage drop from load current (I/R drop) might not be the alternator. A drop from load at idle is somewhat normal, but at higher RPM the alternator should be able to offset the load. If you want to check alternator absolute output, briefly ground the diagnostic terminal on the back of the alternator. The tab is visible through a "D" shaped hole in the rear of the alternator, next to the regulator mounting pad. With a voltmeter connected to the alternator output, briefly insert a short screwdriver to bypass the regulator and operate the alternator at maximum voltage output. The voltage should jump to over 17VDC, so only do this for a second or so. If the voltage doesn't rise, the alternator may be failing. If the alternator output rises as described, the problem is either with the regulator or connections in the system. Since teh regulators usually fail catastophically, if you are getting any output voltage now, the regulator is probably O.K. Check alternator and engine grounding, the alternator output stud connection, battery connections, both the positive power and ground nodes at the body near the battery. A poor connection at any of these points can cause the symptoms you are describing.
While the dash instruments are not highly accurate, the voltmeter is among the more accurate. Even if it does not show the correct voltage, the relative change in the reading from loads is probably close to accurate.
As far as the overheating, the timing seems reasonable. Make sure the coolant is full and flowing throught the radiator. Remove the radiator cap and start the engine, allowing it to warm up. As the thermostat opens, you should be able to see very active flow in the right radiator tank. As you increase engine speed, the tank level should reduce sharply, then rise. If not, the thermostat may be restrictive or the pump may be worn and not moving coolant adequately, or the lower radiator hose may be collapsing from the pump suction.
Make sure that air can flow freely through the radiator. Check for obstructions and debris buildup in front of the radiator and between it and the air conditioning condenser. Make sure the lower air deflector on the lower radiator support is in position and not damaged.
The fan(s) will not start until the temperature is at or above 220°F on most TPIs, and TBI is likely similar. If your temperature geos way above that with no fan start, the switch or CTS might be suspect.
If the coolant is flowing well and the upper radiator hose is hot from the open thermostat, the next possible problem is scale and corrosion buildup in the radiator and/or block which is not allowing effecient heat transfer. You could try flushing with an acidic cleaner, then neutralize and flush with clear water, but a scaled radiator is very difficult to clean in that manner. The most effective means is a tear-down and recore, rodding out the existing core, or caustic chemical boiling of the radiator. Any of these are typically radiator shop specialty services. A replacement radiator can often be cheaper than a recore service.
A little more detail on the symptoms would be beneficial so that more specific suggestions can be offered.
------------------
Later,
Vader
------------------
"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0
12-26-2000, 07:08 PM
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Thanks for the info thus far.
The negative battery ground is good; I hook up my timing light to that. As for the alternator I'm not sure about.. I'll have to do some looking around. I have noticed however a single wire that's near the alternator that's not connected to anything. It doesn't appear to fit into anything I can see. It's bothered me some that there would just be a wire hanging out like that, but I can't think of what it hooks up to. I'll try to find a way to get a picture of it up sometime so you can see what I'm talking about.
More detail.. hmm...
It's getting a bit cold out around here now, so it takes the engine a while to warm up. However when it does warm up the temperature stays between 230-240. (Those are the fan cutoff/cuton points.) Even if I drive it like an idiot for an hour and waste a lot of gas, the temperature never goes into the redline. It seems to me that the ability to cool is there... otherwise heavy loads, I would think, would cause the car to overheat. There's no knock or pinging at the higher-than-usual temperatures, the car still runs smoothly, so it doesn't appear to be causing any problems with my car. (Other than power loss and shorter life span.) The radiator fluid is full and that nice eerie green color with no signs of rust or debris in the fluid. I haven't checked the radiator itself yet, or any of the hoses. (I know the top hose gets hot though, so there's at least fluid going into the top hose. (Can't say much about the bottom hose though.)
You say the fan is supposed to cut on at or above 220.. My fan first turns on at or around 240, constantly.
It's hard to point out any symptoms really, as the car runs fine and smoothly, just with a higher than I like temperature.
I'll try your suggestions and then post more later.
The negative battery ground is good; I hook up my timing light to that. As for the alternator I'm not sure about.. I'll have to do some looking around. I have noticed however a single wire that's near the alternator that's not connected to anything. It doesn't appear to fit into anything I can see. It's bothered me some that there would just be a wire hanging out like that, but I can't think of what it hooks up to. I'll try to find a way to get a picture of it up sometime so you can see what I'm talking about.
More detail.. hmm...
It's getting a bit cold out around here now, so it takes the engine a while to warm up. However when it does warm up the temperature stays between 230-240. (Those are the fan cutoff/cuton points.) Even if I drive it like an idiot for an hour and waste a lot of gas, the temperature never goes into the redline. It seems to me that the ability to cool is there... otherwise heavy loads, I would think, would cause the car to overheat. There's no knock or pinging at the higher-than-usual temperatures, the car still runs smoothly, so it doesn't appear to be causing any problems with my car. (Other than power loss and shorter life span.) The radiator fluid is full and that nice eerie green color with no signs of rust or debris in the fluid. I haven't checked the radiator itself yet, or any of the hoses. (I know the top hose gets hot though, so there's at least fluid going into the top hose. (Can't say much about the bottom hose though.)
You say the fan is supposed to cut on at or above 220.. My fan first turns on at or around 240, constantly.
It's hard to point out any symptoms really, as the car runs fine and smoothly, just with a higher than I like temperature.
I'll try your suggestions and then post more later.
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