i decided to write this as to help numerous owners on here to diagnose thermostat problems.
the thermostat is basically a mechanical valve that opens and closes in relationship to engine temperature,letting water to go to radiator to be cooled, so as to keep the engine running at near enough its optimum temperature
usually around 80c to 90 c depends on diesel or petrol
a faulty thermostat will give cool running of engine therefore give the engine management system signals through temperature sensor, that the engine is still warming up so it will fuel accordingly.....using more fuel affecting drivability,and in winter heater not as good as it should be
remember this simple test is suitable for 99.9% of all engines that are water cooled
thermostat is not an on/off valve it opens and closes to keep engine temp constant,in very cold weather it may be just half way open to restrict flow to radiator ,in hot weather it will be fully open
any of you see ya temp rise when car is stationary to 90 ish and when you drive off it drops down to 70ish means stat cant respond so its duff
THIS TEST SHOULD BE DONE FROM COLD PREFARABLY NEXT DAY IN MORNING and only after doing test by the letter then ask questions!!!!!!!!!
make sure heater is turned OFF this will help to speed process up of warming up
from cold start engine up and warm engine up
as engine warms up feel the top hose of the radiator(this hose is about 2" in diameter) and this should be cold (thermostat working)
if hose warms up with engine ,this means thermostat is passing and will need replacing
if your thermostat is working correctly after about ten minutes of warming up (depending on ambient temperature) hose should start getting warm as thermastat lets water through ,so just have a quick look to see what temperature gauge is at ,this should be around 90c or mid point on gauge depends on engine type
if anyone like to add anything or criticise this please do
REMEMBER THIS THO PLEASE this thread is to check thermostats basic operation is correct
it wont diagnose water pump problems ,radiator problems ,air locks
and also a sticking thermostat
thermostats are relative easy to replace and inexpensive to replace
with the basics of hand tools and knowledge compared to above..
so if you have any problems mentioned in this last part of this
thread by all means use this thread to check your stat ................
then start a new thread asking questions regards your problem
knowing your thermostat is working correctly!!!!!!!
symptons of thermostat can usually be engine taking long time to get up to temperature or not!
also engine temperature mid way on gauge round town ie stop start traffic and soon as open road comes temperature dropping instead of it staying mid way ,,,,,,reason for this is radiator is designed to be capable of cooling engine efficiently at maximum performance plus a bit more ....
Radiator size is designed as such to cool whatever heat generated by engine in question
now this is where thermostat comes in ,this opens and closes to to a degree to keep temperature at a reasonable constant ie diesels at about 80c and petrol at 90c (these being approximate values)