Cooling system desperation!
Kapoho
10-12-2003, 11:23 PM
This problem may not be specific to make and model but just for the record, we’re talking about a ’92 Toyota Previa. LE model, no supercharger.
Never had a problem with the cooling system; always runs at half-mast on the temp gauge. One day about 6 months ago, we’re driving along and the temp starts to go up. Fast. So I turned off the AC, and turned on the heater. Immediately, the temp drops to normal. Tried the heater trick again: turn it off, temp rises. On, temp goes down.
When we got home I was surprised to note that there was no pressure in the system. I removed the surge-tank cap and the gasket looked a little funky so I replace the cap, topped up the coolant, and no problem for six months. Yesterday, we took off on an intended 250-mile trip. Got 40 miles out and the temp started to climb. Did the heater trick again and same results. This time the temp was not so easy to keep down, but we did nurse it home in the top of the safe zone. Shut down the engine and again, no pressure.
I thought maybe the thermostat was not opening and then turning on the heater would allow the coolant to get somewhat cooled by the heater even though it was not circulating through the radiator. I replaced the thermostat, and while I was at it, I thoroughly flushed the system, removed and cleaned out all the little orifices in the surge tank, put it all back together, refilled the coolant, took a 20 mile test drive and same results. Still overheats. Still no pressure in the system.
Coolant shows no signs of combustion products. It was a little bit black, but slightly and I doubt it has been changed in 100K miles. No greasy residue inside the surge tank. No moisture in the tailpipe. Engines runs smooth as silk.
HELP!
Never had a problem with the cooling system; always runs at half-mast on the temp gauge. One day about 6 months ago, we’re driving along and the temp starts to go up. Fast. So I turned off the AC, and turned on the heater. Immediately, the temp drops to normal. Tried the heater trick again: turn it off, temp rises. On, temp goes down.
When we got home I was surprised to note that there was no pressure in the system. I removed the surge-tank cap and the gasket looked a little funky so I replace the cap, topped up the coolant, and no problem for six months. Yesterday, we took off on an intended 250-mile trip. Got 40 miles out and the temp started to climb. Did the heater trick again and same results. This time the temp was not so easy to keep down, but we did nurse it home in the top of the safe zone. Shut down the engine and again, no pressure.
I thought maybe the thermostat was not opening and then turning on the heater would allow the coolant to get somewhat cooled by the heater even though it was not circulating through the radiator. I replaced the thermostat, and while I was at it, I thoroughly flushed the system, removed and cleaned out all the little orifices in the surge tank, put it all back together, refilled the coolant, took a 20 mile test drive and same results. Still overheats. Still no pressure in the system.
Coolant shows no signs of combustion products. It was a little bit black, but slightly and I doubt it has been changed in 100K miles. No greasy residue inside the surge tank. No moisture in the tailpipe. Engines runs smooth as silk.
HELP!
jimmymc
10-15-2003, 09:00 AM
Modern cooling systems are designed to function at or above the ambient boiling point of water/coolant.
Therefore a pressurized system is necessary for the system to function properly. The addition of the heater in the cooling system provides enough additional capacity to limp home.
I would find the leak first...it is probably high in the system...like upper radiator tubes or crack in a tank.
The coolant may evaporate before a drip is evident. When the coolant drops below the level of the leak, only steam escapes.
With engine off, fill the system completely full...buy/borrow a cooling system pressure pump and pressurize the system and inspect it carefully for leaks. Watch the pressure guage on the pump for any drop in pressure...the bottom line is...find the source of the pressure lose problem and go from there.
Other things to look at for overheating at highway speeds.
Not enough coolant circulation-Plugged system, collapsing hose, eroded impeller, erratic thermostat, etc.
Not enough air through radiator fins-Dirty fins, missing air dam parts, bug screens, etc.
Coolant consumption by the engine.
Improper water/antifreeze mixture-too much antifreeze.
Poor heat transfer-Too much paint on radiator tubes/fins, Loose fin to tube contact. Radiator tubes coated on the inside with aluminum oxide.
jimmymc
Therefore a pressurized system is necessary for the system to function properly. The addition of the heater in the cooling system provides enough additional capacity to limp home.
I would find the leak first...it is probably high in the system...like upper radiator tubes or crack in a tank.
The coolant may evaporate before a drip is evident. When the coolant drops below the level of the leak, only steam escapes.
With engine off, fill the system completely full...buy/borrow a cooling system pressure pump and pressurize the system and inspect it carefully for leaks. Watch the pressure guage on the pump for any drop in pressure...the bottom line is...find the source of the pressure lose problem and go from there.
Other things to look at for overheating at highway speeds.
Not enough coolant circulation-Plugged system, collapsing hose, eroded impeller, erratic thermostat, etc.
Not enough air through radiator fins-Dirty fins, missing air dam parts, bug screens, etc.
Coolant consumption by the engine.
Improper water/antifreeze mixture-too much antifreeze.
Poor heat transfer-Too much paint on radiator tubes/fins, Loose fin to tube contact. Radiator tubes coated on the inside with aluminum oxide.
jimmymc
branch
10-26-2003, 10:25 PM
Modern cooling systems are designed to function at or above the ambient boiling point of water/coolant.
Therefore a pressurized system is necessary for the system to function properly. The addition of the heater in the cooling system provides enough additional capacity to limp home.
I would find the leak first...it is probably high in the system...like upper radiator tubes or crack in a tank.
The coolant may evaporate before a drip is evident. When the coolant drops below the level of the leak, only steam escapes.
With engine off, fill the system completely full...buy/borrow a cooling system pressure pump and pressurize the system and inspect it carefully for leaks. Watch the pressure guage on the pump for any drop in pressure...the bottom line is...find the source of the pressure lose problem and go from there.
Other things to look at for overheating at highway speeds.
Not enough coolant circulation-Plugged system, collapsing hose, eroded impeller, erratic thermostat, etc.
Not enough air through radiator fins-Dirty fins, missing air dam parts, bug screens, etc.
Coolant consumption by the engine.
Improper water/antifreeze mixture-too much antifreeze.
Poor heat transfer-Too much paint on radiator tubes/fins, Loose fin to tube contact. Radiator tubes coated on the inside with aluminum oxide.
jimmymc
:smile: you may just have replace the rad cap/ they are rated for a certain pressure so be sure to find out what yours should be
Therefore a pressurized system is necessary for the system to function properly. The addition of the heater in the cooling system provides enough additional capacity to limp home.
I would find the leak first...it is probably high in the system...like upper radiator tubes or crack in a tank.
The coolant may evaporate before a drip is evident. When the coolant drops below the level of the leak, only steam escapes.
With engine off, fill the system completely full...buy/borrow a cooling system pressure pump and pressurize the system and inspect it carefully for leaks. Watch the pressure guage on the pump for any drop in pressure...the bottom line is...find the source of the pressure lose problem and go from there.
Other things to look at for overheating at highway speeds.
Not enough coolant circulation-Plugged system, collapsing hose, eroded impeller, erratic thermostat, etc.
Not enough air through radiator fins-Dirty fins, missing air dam parts, bug screens, etc.
Coolant consumption by the engine.
Improper water/antifreeze mixture-too much antifreeze.
Poor heat transfer-Too much paint on radiator tubes/fins, Loose fin to tube contact. Radiator tubes coated on the inside with aluminum oxide.
jimmymc
:smile: you may just have replace the rad cap/ they are rated for a certain pressure so be sure to find out what yours should be
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