In a perfect environment your  vehicles engine works very hard to maintain a desired operating temperature.

When I was 18 years old still an apprentice I will never forget the time I was looking at my sisters car, it was over heating so I thought I would investigate this problem.

I was about to remove the radiator cap with full knowledge that most radiators caps have a release notch when removing the cap to prevent the pressure of the cooling system spraying hot water every where.

Well I was rotating the cap to release the pressure with the understanding that there was no pressure under the cap, next thing I was overcome by extreme hot water onto my face, this was embarrassing the next thing I remember I was on my way to the Dandenong Hospital, with burns to the face and eyes, this is why its very important to understand the dangers of opening a radiator cap when the engine is hot especially when or if the cooling system is over heating.

The only time to remove a radiator cap is when the engine is cold.

An engine thermostat should never be removed accept when replacing a faulty thermostat, for some reason many people think if they are having a problem with high engine temperature a solution is to remove the thermostat.

The misconception is by removing the thermostat the gauge may decrease from high to normal.

Allow me to explain what happens if a thermostat is removed form an engines cooling system; the water is not transferring hot water from the engine to the radiator as its designed.

The purpose of the thermostat is to hold water in the engine long enough for the molecules to expand then the thermostat will open and allow the hot water into the radiator to cool down and contract, this is in normal operating conditions.

Let me add if the cooling system requires constant topping up this means there is a leak in the cooling system and the potential of rapid cooling and rapid heating, this is where the cylinder head will be exposed to a higher heat range and thus offering the potential warping and or cracks.

The cooling system is designed to maintain a constant desired engine temperature to aid in the ultimate fuel economy as the air to fuel ratio only operates effectively when the engine is operating within this parameter.
Written by Darren Gow-Brown Virtualmechanic.com.au

This issue with the Toyota Camry may cost many motorists a costly mistake if not diagnosed correctly, to all who read this and rectify the problem at minimal cost will be gratful to Neil Gray.

May I add that all Car manufactures, Toyota, Holden, Ford, Nissan, Mitsu, etc should be offering and sending data in the form workshop manuals free of charge to the Virtual Mechanic to help prevent costly mistakes at any workshop or service centre.

I thank Neil Gray for going to the trouble of locating the cause of the high tempreture reading leading to a poor earth connection secured at the engine exhaust manifold.

Written by Darren Gow-Brown
Virtualmechanic.com.au

Name Neil Gray
State & Suburb Brisbane QLD>

Type of Vehicle Toyota
Model Camry
Month/Year 12/1990
Kms 120,000
Problem This is a fuel gauge problem. I have replaced the sensor and the gauge.
The gauge goes to full scale after a short time(1min)
I’ve had the coolant temp checked its O.K
The fans come on O.K if I”m stuck in traffic for a long time and go off when i get rolling.
Please help as motorama don’t know what i’m talking about
ta neil

Your Question does not make sense

No thats because im an idiot Its The TEMPERATURE GAUGE THAT GOES FULL SCALE
Thanks for your patience Darren
Neil Gray

Ok Neil,
 
Now the temperature gauge goes to full in one minute this sounds like its either a faulty gauge or something causing the coolant to rise in temperature
When the cooling fans switch on can you count how many minutes or seconds the thermo fans stay on
 
Darren

i’ve replaced the gauge
the fans stay on  for about 2mins when i get moving.

Darren wrote:
@ minutes is far to long if we use an example of a standard passenger vehicle in normal operating condition its around 40 seconds
therefore you have a cooling system issue

Could it be the thermostat?

Darren wrote:
Yes the best way to measure the thermostat is with the engine at normal operating temp and the engine switched off feel the upper hose and the lower radiator hose and check for a difference in temp
Neil you may also have a blocked radiator to give the same result
D

hi darren,
thanks for the help..i’ll get back to you when it stops raining and i can look at the problem.
thanks again
neil

Hi Darren,

I have replaced temp meter
I have replaced the thermostat
I originally replaced the sensor

The car still runs O.K.
The meter still goes to full scale
The coolant seems to be circulating O.K.

Could it be:-
(1)  Water pump not working efficiently?
(2)  Faulty sensor sold to me new ?
(3) Meter Mother Board in dash?

I am about to attack the horrible thing with a sledge hammer

Hi Darren,

I’VE FIXED IT

Having looked at the electrical wiring diagram I thought it could be that the earth on B5 of the combination meter plug was missing.
This earth comes from a point on the engine manifold at the rear of the engine.
THE EARTH WAS NOT CONNECTED PROPERLY.
THE GAUGE NOW TELLS THE TRUTH

Happy days

Thanks for your efforts on my behalf on this very obscure problem.
I thought you might like feedback on the fix

Hi Darren,
I have added a note to diagram in magenta
Hope this is satisfactory

Hi Neil

I have published your efforts, and hope many people will read this an not make a costly mistake of a Head repair……..

Join the forum discussion on this post - (1) Posts

THINGS TO LOOK FOR
Welsh plugs can leak at normal operating temperature.  When this happens, stop the engine and get the vehicle towed to the garage.

IS IT EXPENSIVE TO REPAIR?
Nearly all welsh plugs are expensive to repair as they are hard to get to.  The welsh plugs themselves cost only a few dollars each but the labour is the expense.  Welsh plugs are either made of brass or steel, cup or dish.  It is best to consult your motor reconditioner to work out which is the best one to fit.

TEMPORARY REPAIR AND LONG TERM REPLACEMENT
If a single welsh plug is found to be leaking it may be a consideration to get all the welsh plugs replaced at the same time.  It really depends on how long you intend to keep the vehicle.  Once any welsh plug is replaced, always change the water and add corrosive inhibitor on a regular basis, eg every 12 months or 10,000-20,000Kms.

THINGS TO LOOK FOR
The water recovery bottle is part of the cooling system.  For this reason caution should be taken when checking the levels as the bottle, if warm, is under pressure.  The best way to completely check the cooling system level is when the engine is cold.  Radiator and water recovery bottle are best to be checked at the same time.  If you need to top up the water level when the engine is warm or hot use caution, as hot water will cause severe burns.  When opening the radiator cap use gloves or a rag or a radiator protector opener.  When filling the radiator or water recovery bottle, leave the engine running as you fill the radiator.  This will prevent the cooling system from any damage to the head.

IS IT EXPENSIVE TO REPAIR?
Replacing the water recovery bottle is around $30.00.  But try to work out why the bottle needs replacing as it may be a repeat situation which may be caused by a cooling system fault.

THINGS TO LOOK FOR
A water pump, over time, may start to leak at normal operating temperature or it may leak several hours after being switched off with no or low pressure.  These are signs not to drive the vehicle and replace the water pump ASAP.  The bearing inside the water pump may fail causing the water pump seal to leak.  This is an urgent sign that it needs repairing as the pump shaft may end up towards the radiator causing more damage to the cooling system.  If the shaft bearings collapse then the whole shaft may move away from the water pump and end up with the fan in front of the radiator.

IS IT EXPENSIVE TO REPAIR?
Replacing the water pump may be expensive if the pump is connected to a timing bell or behind several brackets, it could cost up to $300.00.  But if it’s an easy water pump to get to it may only cost around $150.00 provided that no bolts snap and some bolts may be corroded.  The cost will also vary depending on the make and model of the vehicle.

TEMPORARY REPAIR AND LONG TERM REPLACEMENT
If a water pump is leaking from a pin hole then it may be welded but this could affect the seals as it’s being welded.  But it’s worth a try if the pump costs around $300.00.

THINGS TO LOOK FOR
The colour of the water tells a very good story about the condition of the cooling system.  Brown water is the worst, clear water is not good; green water is best and it needs to be changed every 12 months to keep the colour at its best.

IS IT EXPENSIVE TO REPAIR?
If your vehicle is pre 1990 then a good corrosive inhibitor, eg Castrol, may be okay.  If it is after 1990 then contact your dealer as the seals and welsh plugs require specific inhibitors to protect these components.  These additives may be expensive.

TEMPORARY REPAIR AND LONG TERM REPLACEMENT
If your vehicle has brown water, disconnect the heater hose and remove the radiator cap and secure a garden hose in the heater hose and turn on a moderate pressure.  This is the best way to reverse flush the cooling system.  Please note: this should only be done when the engine is cold.  It may require several applications until the water runs clear.  It is a good idea to turn the heater tap as this will also flush the heater core, in case it might be partially blocked.

THINGS TO LOOK FOR
A viscose fan should cut in and out, if monitored over 1/2 hr of the engine idling.  Use extreme caution with the viscose fan or any fan blade when checking.  The best way to check the fan is to idle the engine for about 1500 revs per minute to 2000 and you will notice when revving the engine while hot, more of a fan noise will be apparent.  Then when the cooling system cools down the viscose fan is not consuming any energy from the fan belt or water pump pulley.  A viscose fan may also cause the engine to overheat at moderate to high speed.

IS IT EXPENSIVE TO REPAIR?
Viscose fans may be expensive to repair depending on the make and model.  It’s always a good idea to replace a viscose fan with the original type.  They could cost around $150.00.  Getting one from the wreckers is not recommended as most of these fans are faulty.

TEMPORARY REPAIR AND LONG TERM REPLACEMENT
If you are stranded and the fan is locking up, cooling the radiator, then you can try overhauling the viscose fan and putting a bolt in to prevent it from free wheeling just to get you around.  But it does affect your fuel economy.

THINGS TO LOOK FOR
If you decide to put another radiator hose on.  What you  need to do is feel the upper and lower radiator hoses at normal operating temperature, very carefully, just in case the radiator explodes, and they should be almost the same temperature.  If one is cold and one is hot, this is an indication of a sticking thermostat.

COST
To replace the thermostat it will cost $30.00-$90.00 depending on the make and model of the vehicle and also depending on how old the vehicle is.  The thermostat housing bolts may break as you try to remove them.

The thermo fan switch when it reaches its designed temperature is designed to switch on and when it reaches a lower temperature, it is designed to switch the power off.  The thermo fan switch receives power from the fuse box.  When it reaches a temperature the switch will bridge the terminals thus turning the thermo fan on.

THINGS TO LOOK FOR

Check that the connections are secure and observe that the thermo fan is switching on and off.  Sometimes this may not occur and just manipulating or wiggling the terminals may cause the fan to switch on.  If this is the case then take the terminal off and clean it and refit it.  Otherwise replacing the switch might be another option.

IS IT EXPENSIVE TO REPAIR?

A thermo fan switch is a costly item at around $60.00-$90.00.  It’s better to buy the same type of switch as the original.

TEMPORARY REPAIR AND LONG TERM REPLACEMENT

If stranded the switch may be bypassed and the terminals bridged, but remember this will put a load on the battery and will always turn the fans on when the ignition is turned on.  Or on some vehicles, if you bridge the terminals it may stay on indefinitely.

THINGS TO LOOK FOR
As the thermo fan operates over years the internal mechanisms may start to wear and cause a resistance in the thermo fan relay causing an overload on to the relay and the fuse.  A common sign is a faulty relay.  Melted terminals on the relay indicate that the thermo fan may be overloading the system or drawing too much current caused by an internal fan problem.

IS IT EXPENSIVE TO REPAIR?
If it is a standard thermo relay it may cost around $20.00.

TEMPORARY REPAIR AND LONG TERM REPLACEMENT
If all other relays are the same specs, ie they may have 30 or 60 amps, make sure that the thermo fan relay is the same as the other and then just swapping the relay with another just to get you home if you’re stranded.