car overheating only sometimes
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Senior Member
Joined: Feb 2000
Posts: 581
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From: US
Car: 86 iroc
Engine: 305
car overheating only sometimes
I have a 86 lg4 iroc and all is fine until the temp outside goes above 85,which its only done a few times here.So when its 90 all the time Im gonna really have problems.It runs at 180-200 but when it gets hot out and I drive alot its hitting 220-260 in traffic,If I turn the heat on and move I can get it down to around 220 but no lower on hot days.It wasnt like this last summer,had no problems and it stayed around 185-200 all the time,sometimes cooler.Is this a bad thermostat?Its about 4 ears old so I guess its time.I have replaced the water pump,heater core and radiator in the past year.The single fan seems to be working right.It has a 185off-200on switch in it I think.thanks
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Joined: Mar 2001
Posts: 652
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From: Virginia
If the fan is cutting on at 200 degrees and the temp is STILL RISING, even in traffic you have other issues. Are you positive the fan is cutting on?
Are you going by the less than accurate factory gauge? BEFORE you replace / fix anything, I'd verify temp with a mechanical gauge.
That being said, if it's still hot, the usual suspects are:
- Radiator Cap -
often overlooked to fix an overheat problem. What happens, the cap keeps the cooling system under pressure, which allows it to do it's job. If not under pressure the water / coolant would boil alot sooner. A slow, often unnoticeable leak in the cap can cause major headaches. If your looks old / original, go ahead and spring for a new one.
- Hoses -
A collapsed hose will cause problems. Make sure your hose isn't collapsing on itself when hot. Normally there is a spring in the lower hose to prevent just that.
- Thermostat -
Even brand new one's out of the box can be bad. I don't EVER buy a cheap thermostat, simply because it's a pain to have to change it again if it fails. Buy a premium store thermostat or even better, an AC Delco. If going AC Delco, go for a 170 degree.
- Water pump -
When in traffic, the cooling system relies more on the water pump to do it's job. A pump that isn't up to snuff will not move the coolant through the radiator fast enough to get it cooled down before it heats up too much in the engine. There are simple, rivet on little plates that greatly improve flow of a stock type water pump.
- Radiator -
Once drained, take a look in it with a flashlight, if you see alot of scaly, slimy buildup, time to spring to have it cleaned out ( @$40 ) or better yet @$120 for a new replacement, and use distilled water after installation and flush and you won't have that problem again.
ALSO...it might be worth it to check the front of the radiator , between the AC condensor for leaves, trash etc blocking flow to the radiator, this will especially hurt low speed cooling, since the lower air dam helps cooling at speed.
Also check to make sure you don't have alot of bent / broken fins on the radiator. This can cause problems as well. If you do, they make a cheap tool to straighten the fins, or just use another tool and be careful.
A good backflush and fill is always my first step on a cooling system. You can get a backflush kit for cheap. Run the cleaner that comes with it... you'll be surprised of the crap that comes out, make sure the heater is on wide open to clean the heater core out as well.
HTH and good luck
Are you going by the less than accurate factory gauge? BEFORE you replace / fix anything, I'd verify temp with a mechanical gauge.
That being said, if it's still hot, the usual suspects are:
- Radiator Cap -
often overlooked to fix an overheat problem. What happens, the cap keeps the cooling system under pressure, which allows it to do it's job. If not under pressure the water / coolant would boil alot sooner. A slow, often unnoticeable leak in the cap can cause major headaches. If your looks old / original, go ahead and spring for a new one.
- Hoses -
A collapsed hose will cause problems. Make sure your hose isn't collapsing on itself when hot. Normally there is a spring in the lower hose to prevent just that.
- Thermostat -
Even brand new one's out of the box can be bad. I don't EVER buy a cheap thermostat, simply because it's a pain to have to change it again if it fails. Buy a premium store thermostat or even better, an AC Delco. If going AC Delco, go for a 170 degree.
- Water pump -
When in traffic, the cooling system relies more on the water pump to do it's job. A pump that isn't up to snuff will not move the coolant through the radiator fast enough to get it cooled down before it heats up too much in the engine. There are simple, rivet on little plates that greatly improve flow of a stock type water pump.
- Radiator -
Once drained, take a look in it with a flashlight, if you see alot of scaly, slimy buildup, time to spring to have it cleaned out ( @$40 ) or better yet @$120 for a new replacement, and use distilled water after installation and flush and you won't have that problem again.
ALSO...it might be worth it to check the front of the radiator , between the AC condensor for leaves, trash etc blocking flow to the radiator, this will especially hurt low speed cooling, since the lower air dam helps cooling at speed.
Also check to make sure you don't have alot of bent / broken fins on the radiator. This can cause problems as well. If you do, they make a cheap tool to straighten the fins, or just use another tool and be careful.
A good backflush and fill is always my first step on a cooling system. You can get a backflush kit for cheap. Run the cleaner that comes with it... you'll be surprised of the crap that comes out, make sure the heater is on wide open to clean the heater core out as well.
HTH and good luck
Thread Starter
Senior Member
Joined: Feb 2000
Posts: 581
Likes: 0
From: US
Car: 86 iroc
Engine: 305
all the the stuff you mentioned has been replaced within the last year,when I did the pump I replaced all the hoses and have checked them.I just replaced the radiator and cap less then 6 months ago.I know new stuff can go bad.The weird thing if I didnt make it clear before is it doesnt do it on every warm-hot(80-90) day.Yesterday was the first day it got way to hot,it was almost in the red while in traffic still.I had driven the car alot before it happen,like 5 hours in town and the car is never driven much,my other car is dead.When it does cool down it does it all at one time and real quick.Thats why I was thinking thermostat because maybe its sticking and then finally opening.I will get a new one and see.
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