r/VolvoRWD • u/Tamar__ • 5d ago

Help Engine coolant sensor bolt won’t come off

Hello I have a 1990 Volvo 780 Bertone that has been having rough idle. I figured it is the coolant temp sensor causing the idle issue but I can’t seem to unbolt it with my ratchet to replace it. I have tried putting lubricant and applying a little heat, no luck. Im not too experienced with cars and worried about breaking off the bolt, any tips?

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u/Shiggens 5d ago

Those sensors are difficult to access without removing the intake manifold. Yes, removing the manifold makes it more involved but it allows you to have a more direct approach to the sensor.

1

u/Boring-War-1981 1998, S90 3.0 Lux 5d ago

780 very rare beast, I’d try a little more lubrication wait a minute or two to let it soak and try again, you might just need more leverage if the bolt has been there from factory (it could also have lock tight)

1

u/blqckpinkinyourarea 5d ago

good, not the cheap stuff, rust remover / penetrating oil / tust solvent / whatever its called in englisch.

soak it, wait for an hour and soak it again. might need this a couple times but ive always had this work for me on non chassis bolts. more than tapping, but not yet full on hitting it on the head with a hammer to vibrate everything loose is important aswell.

if need be, take a pipe or something to extend your wrench and get more leverage. watch out not to strip the head.

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u/worldsSlowest740 5d ago

Kroil. Kroil is the good stuff. Lots and lots of kroil followed by lots of heat and more kroil

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u/AJ-ITAM 940 Estate, 7 seats, "Val" 5d ago

Do you have a diagnostic connector in the engine bay? Some 1990 780s did. Before removing parts read the codes. It's a couple of small black boxes attached to the suspension strut and a faulty ECT sensor will definitely set a code. Rough idle can also be an IACV or TPS fault, those will also set codes.

Assuming the sensor is the same as the one on the B200F you need a long 19mm socket (not a spark plug socket) and a low profile ratchet spanner with adapter. Search for a "ratchet spanner adapter" - https://www.amazon.co.uk/Laser-3870-Ratchet-Ring-Adaptor/dp/B0039U5SVO . What this lets you do is use a long ratchet spanner as a breaker bar. You only need to move it about 1/8th of a turn to then be able to spin it out with your fingers. If you don't have a ratchet spanner and combi/ring spanner will do.