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Old 05-26-2006, 03:01 AM
deserthonda's Avatar
Been Around A Long Time Member
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Join Date: Dec 2005
Location: In The Desert ( Sahara ? )
Posts: 4,754

With summer coming i thought it might be a good idea to explain how to diagnose a stuck open or closed t-stat ..and how to replace it ,,if needed so..
I am sure most of you already know this,, but for those who do not ,, i hope this will help you out

First off,, t-stat starts to open at around 170* F
and it is fully open at around 194 * F

T-stat location accord 4 cylinders

up to 1989, it is located at the end of top radiator hose ( engine side ) in t-stat housing

1990 and newer it is located at the end of the lower radiator hose ( engine side ) in t-stat housing

t-stat stuck open

the t-stat will not fully close when coolant temperature is below the opening setting 170 degree F ,,,This will allow coolant to flow through the radiator while the engine is still cold thus taking too long to warm up,it might prevent the engine to reach normal operating temperature ,,

Symptoms of a stuck open T-stat..

a very long time to reach operating temp

during cold weather the heater output temp will not get warm BRRRRRRR,,,

the lower radiator hose begins to get warm as soon as engine is run for just a little while

the temp gauge inside the car will be at 1/4 or below

T-stat stuck closed

t-stat will not open during engine warm up. The engine will warm up at normal rate . however when it reaches normal operating temperature , it will overheat quickly,,, All coolant flow to radiator is blocked

Symptoms of stuck closed T-stat

engine will overheat,

the lower hose will remain cool even after engine is fully warmed up,

temp gauge inside the car will reach the H ..

fans will not come on

could crack top radiator tank ( plastic tanks )

.could cause a blown head gasket


I am only going to give directions for 90 and newer accords ,,not too may 89 or older ,,if you own an 89 or older and would like direction ,, PM me ,, and i will gladly help you..

starting in 1990.. honda moved the t-stat housing and of course the t-stat,, at the end of the lower radiator hose ( engine side ) ,, up to 1989 t-stat housing used to be at the end of top radiator hose ( engine side)

it will be a lot easier to remove the air intake tube , it will give you a lot more room to replace the t-stat, remove the clamp for the lower radiator hose, remove the 2 10mm bolts for the outer part of the t-stat housing, in some years you got to disconnect the plug for the fan switch and the ecu ground wire ,, 10mm bolt as well..anyho , when all the bolts are removed,, replace the t-stat, reinstall in reverse order,, DO NOT forget to reconnect ground wire and to plug in the fan switch ..
I would reccomend that you use a Honda t-stat, it comes with a new gasket,,, make sure the pin is at the top side
Once t-stat is installed, loosen the cooling system bleeder screw 12 mm ,, on top of t-stat housing, do not totally remove it , remove radiator cap, add coolant 50/50 mix .
fill radiator till only coolant comes out of bleeder screw no air bubbles, tighten the bleeder screw, top off the radiator, install cap, start car and chk to make sure there are no leaks ...........Let car get warm .. lower hose should start to feel hot but not as hot as top hose ,, if so it is an indication that t-stat is opening up properly ,,

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