9 replies to this topic

[Malinda]

Hi,

I got 1999 Rover MPI. It was running smoothly until yesterday when started over heating.

Problem: can see coolant in expansion tank boiling, though the temperature gage is at half.

Things I tried:
1. Flushed the radiator
2. replaced the thermo stat valve with a 74 degree one
3. cleaned the out side of radiator
4. checked all horses and found no leaks
5. checked the coolant bottle in cold run and observed no bubbles to make sure that the head gasket is good
6. changed the coolant
7. checked the radiator fan and observed that it starts running when the temp gauge hits near to half
8. checked the expansion tank in cold run and observed water is circulating, thus I concluded that the water pump is in order

After doing all I kept the front grill removed, kept the bonnet opened and ran the engine for 15 mins and observed that boiling again though the temp gauge shows half.
Please help me in diagnosing this problem.
Regards,

Malinda

[miniboy1971]

Have you changed the black cap on the expansion tank ? These have a built in pressure relief valve which can seize up over time and will cause the boiling you describe.

They're about £ 6 + P&P from Minispares

http://www.minispare.....WINPOINT EX...

I'd try this first before doing anything else......

[Sprocket]

Replace the 74 stat with the correct 88 stat, you will suffer over fueling otherwise.

Normally when the coolant temp sensor fails, it fails reading low, if its a total failure of the sensor it will either go open circuit and read low all the time, or short circuit and read high all the time. However, most of the time it reads lower than actual temperature.

Have you measured the actual coolant temperature with an acurate digital thermomenter?

Change that thermostat back

[Malinda]

Have you changed the black cap on the expansion tank ? These have a built in pressure relief valve which can seize up over time and will cause the boiling you describe.

They're about £ 6 + P&P from Minispares

http://www.minispare......WINPOINT EX...

I'd try this first before doing anything else......

going to order it. thanks

[Malinda]

Replace the 74 stat with the correct 88 stat, you will suffer over fueling otherwise.

Normally when the coolant temp sensor fails, it fails reading low, if its a total failure of the sensor it will either go open circuit and read low all the time, or short circuit and read high all the time. However, most of the time it reads lower than actual temperature.

Have you measured the actual coolant temperature with an acurate digital thermomenter?

Change that thermostat back

did not measure the actual temperature. apparently i found that the electric fan is not operating in the right speed now. I think i should change the fan motor and temperature sender.

by the way, 88 degree thermostat is too much for a hot country like mine. with 88 degree thermostat the temperature stabilizes above the half mark in the gauge.

thanks,

Malinda

[Sprocket]

Replace the 74 stat with the correct 88 stat, you will suffer over fueling otherwise.

Normally when the coolant temp sensor fails, it fails reading low, if its a total failure of the sensor it will either go open circuit and read low all the time, or short circuit and read high all the time. However, most of the time it reads lower than actual temperature.

Have you measured the actual coolant temperature with an acurate digital thermomenter?

Change that thermostat back

did not measure the actual temperature. apparently i found that the electric fan is not operating in the right speed now. I think i should change the fan motor and temperature sender.

by the way, 88 degree thermostat is too much for a hot country like mine. with 88 degree thermostat the temperature stabilizes above the half mark in the gauge.

thanks,

Malinda

Its up to you but you could at worst, bore wash the engine to death

The injection engine NEED the 88 stat to operate correctly.

If the thermostat is operating correctly and the engine still overheats, it is not the fault of the thermostat, there is something else fundamentaly wrong. Basicaly whether it is the 74c or the 88c stat, if the stat is full open and the engine is still overheating, the problem is else where. You have already proven that it is not the thermostat as it still aparently overheats

Consider putting the 88c stat back in

[tmsmini]

I have found that the standard thermostat works well in the California summers. We have regular temps in the 90s F and periods over 100 F.

My son and I took a trip over the Sierra Nevada and down the back side of the Sierra to southern California a few years ago. Temperatures over 100 most of the way and about 8 hours driving time. The car did better than we did.

Edited by tmsmini, 04 May 2009 - 01:43 PM.

[Malinda]

I have found that the standard thermostat works well in the California summers. We have regular temps in the 90s F and periods over 100 F.

My son and I took a trip over the Sierra Nevada and down the back side of the Sierra to southern California a few years ago. Temperatures over 100 most of the way and about 8 hours driving time. The car did better than we did.

yeah even in Sri Lanka standard 88 degree thermo works fine unless you continuously drive in Colombo city traffic jams often.

[bigmotherwhale]

all thats wrong is the expansion tank releif valve i had the same problem, the fan wont come on because the water can get abouve 100 degrees celcius becuse its not under pressure, i think the mpi fan is set at 102 degrees c.

change the cap first before spending any more money.

[tmsmini]

After thinking about it, the duration of my drive has nothing to do with the thermostat and heating/cooling. On a long drive the car reaches a steady state that the cooling system should be able to cope with.

All the thermostat does is get the car up to the proper operating temperature quickly. Once at the operating range then the cooling system keeps the system within range.

I would replace the cap also. One time after some work I did not tighten the cap properly and the low pressure allowed boiling.