temp variations
Thread Starter
Instructor
Joined: Oct 2004
Posts: 208
Likes: 1
From: Santa Rosa CA
temp variations
My temp gauge varies a lot, steady speed down the freeway and it may go from 180 – 220 for no apparent reason. Radiator is clean of debri, main fan comes on about 225°. Replaced the radiator cap and thermostat as well as the temp sensor the the aux fan that had cracked. Does a water pump get less efficient over time? If I take the radiator cap off and run up the idle there seems to be plenty of water circulation. No unusual noises. Bad gauge or temp sensor for gauge?
Thanks for any ideas.
Thanks for any ideas.
Melting Slicks
Joined: Jan 2001
Posts: 2,940
Likes: 5
From: Chesapeake VA
As long as you are getting good airflow through the radiator on the highway, your car should stay pretty close to the thermostat temp.
As you probably know, once you drop below 40MPH on a hot day, the car will not cool efficiently, and the temp will rise until the radiator fan comes on.
If it is varying on the highway as you described, I would try changing the thermostat again, just too rule that out.
As you probably know, once you drop below 40MPH on a hot day, the car will not cool efficiently, and the temp will rise until the radiator fan comes on.
If it is varying on the highway as you described, I would try changing the thermostat again, just too rule that out.
Thread Starter
Instructor
Joined: Oct 2004
Posts: 208
Likes: 1
From: Santa Rosa CA
As long as you are getting good airflow through the radiator on the highway, your car should stay pretty close to the thermostat temp.
As you probably know, once you drop below 40MPH on a hot day, the car will not cool efficiently, and the temp will rise until the radiator fan comes on.
If it is varying on the highway as you described, I would try changing the thermostat again, just too rule that out.
As you probably know, once you drop below 40MPH on a hot day, the car will not cool efficiently, and the temp will rise until the radiator fan comes on.
If it is varying on the highway as you described, I would try changing the thermostat again, just too rule that out.
Drifting
Joined: Sep 2003
Posts: 1,363
Likes: 7
From: 1994 LT1 Coupe 6-speed with FX3 & 2000 LS1 Vert 6-Speed with F45 Hunterdon County, NJ
Presume your car is an 89 with the L98 engine (per your profile)...
Are the temps from the digital dash coolant temp or analog coolant temp gauge?
I doubt a water pump or thermostat could cause the temps to change that drastically in a matter of seconds...
Most likely it is the temp sensor.
Since coolant temp sensors resistance is inversely proprotional to coolant temperature (i.e. as the temp goes up, the resistance goes down), and assuming the temp is 'bouncing' up and then settling back down to normal, it would rule out a short, and corrosion on the connector and contacts and a bad ground as all would increase resistance and thereby temp reading.
So, my money would be the coolant temp sensor.
Not sure where the temp sensors are on your L98, but could be in the water pump or drivers side head.
Perhaps of help in locating yours, On 94 LT1's, the water pump sensor is for the digital dash and the sensor on the passenger side head is for the analog coolant temp gauge.
Are the temps from the digital dash coolant temp or analog coolant temp gauge?
I doubt a water pump or thermostat could cause the temps to change that drastically in a matter of seconds...
Most likely it is the temp sensor.
Since coolant temp sensors resistance is inversely proprotional to coolant temperature (i.e. as the temp goes up, the resistance goes down), and assuming the temp is 'bouncing' up and then settling back down to normal, it would rule out a short, and corrosion on the connector and contacts and a bad ground as all would increase resistance and thereby temp reading.
So, my money would be the coolant temp sensor.
Not sure where the temp sensors are on your L98, but could be in the water pump or drivers side head.
Perhaps of help in locating yours, On 94 LT1's, the water pump sensor is for the digital dash and the sensor on the passenger side head is for the analog coolant temp gauge.
Thread Starter
Instructor
Joined: Oct 2004
Posts: 208
Likes: 1
From: Santa Rosa CA
Yes, it is an ’89, I should have made that clear. It is a digital dash. There is a sensor on the passenger side head that I believe is temp. I will try to find one of those. I have also just noticed that it is pushing a lot of coolant into the coolant tank, sometimes overflowing it with a loss of some coolant and sucking the remainder back as it cools, I am beginning to fear to a head gasket problem. What is a good test for that problem? I has been a good vehicle, bought it new, but it does have 150K miles.
Drifting
Joined: Sep 2003
Posts: 1,363
Likes: 7
From: 1994 LT1 Coupe 6-speed with FX3 & 2000 LS1 Vert 6-Speed with F45 Hunterdon County, NJ
Easy way to be sure if it is the correct sensor is to check temp via dash, unplug it, and see if temp suddenly changes.
Re: overflow overflowing -- could also be just a bad radiator cap -- suggest having the cap tested or just trying a new ACDelco brand cap and see if the problem goes away (many are having problems with other brands).
If the problem remains, there is a test solution/paper which can test for exhaust gases in the coolant (a classic result when a head gasket leaks compression) -- should be available at your local parts houses.
Alternatively, you could pull the spark plugs (ideally when cold to not damage the threads) and run a compression test... Compression gauges are usually available at tool places (parts house, sears, snap-on truck, etc).
Re: overflow overflowing -- could also be just a bad radiator cap -- suggest having the cap tested or just trying a new ACDelco brand cap and see if the problem goes away (many are having problems with other brands).
If the problem remains, there is a test solution/paper which can test for exhaust gases in the coolant (a classic result when a head gasket leaks compression) -- should be available at your local parts houses.
Alternatively, you could pull the spark plugs (ideally when cold to not damage the threads) and run a compression test... Compression gauges are usually available at tool places (parts house, sears, snap-on truck, etc).
Thread Starter
Instructor
Joined: Oct 2004
Posts: 208
Likes: 1
From: Santa Rosa CA
theadmiral94
Great minds think alike; I changed the radiator cap a few days ago, no help, and have a friend coming over tomorrow with a test kit to do the exhaust check in the radiator and do a compression check. Had not thought of the simple trick of disconnecting the sensor to check the gauge though, thanks. But it is looking like I will be changing a head gasket. I am an amateur mechanic; I think the last time I bolted on a head was about 1968 on a 327.
Great minds think alike; I changed the radiator cap a few days ago, no help, and have a friend coming over tomorrow with a test kit to do the exhaust check in the radiator and do a compression check. Had not thought of the simple trick of disconnecting the sensor to check the gauge though, thanks. But it is looking like I will be changing a head gasket. I am an amateur mechanic; I think the last time I bolted on a head was about 1968 on a 327.
Thread Starter
Instructor
Joined: Oct 2004
Posts: 208
Likes: 1
From: Santa Rosa CA
I think I have confirmed a bad head gasket. Lots of coolant being pumped into overflow tank, bubbles noticed in radiator, block test fluid indicates exhaust gas coming into radiator. Thanks for the help, I guess I have a little project as soon as I get some free time and get in the right mood.
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Pro
Joined: May 2006
Posts: 536
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From: Humble Texas
theadmiral94
Great minds think alike; I changed the radiator cap a few days ago, no help, and have a friend coming over tomorrow with a test kit to do the exhaust check in the radiator and do a compression check. Had not thought of the simple trick of disconnecting the sensor to check the gauge though, thanks. But it is looking like I will be changing a head gasket. I am an amateur mechanic; I think the last time I bolted on a head was about 1968 on a 327.
Great minds think alike; I changed the radiator cap a few days ago, no help, and have a friend coming over tomorrow with a test kit to do the exhaust check in the radiator and do a compression check. Had not thought of the simple trick of disconnecting the sensor to check the gauge though, thanks. But it is looking like I will be changing a head gasket. I am an amateur mechanic; I think the last time I bolted on a head was about 1968 on a 327.
im a self tought mechanic, and my 96 has never seen a dealership or
mechanic, i have the exact problem, but started from engine overheating... white smoke out of the exhaust,and while engine is cold bubbles ,and burping coming from radiator and over flow tank..
with new pump and therms. i like you use to build early chevy engines
this will be a new challenge....
