Water Thermostat Replacement


Thermostat £15 and replacement gasket £4

Optional – New chrome water neck or housing at £21

Optional – Water sender switch £9


The engine is being refurbished and it’s a good idea to replace old parts that have been standing for years. As I wanted a little chrome I decided to get a new chrome water neck while I was at it as the old one looked quite corroded. My other little optional extra was the water temperature sender switch I replaced hole there was no water in the engine.


I will assume that you are starting from scratch  with the engine in place, as my engine is out it’s easier to see but the process is exactly the same.

You can either replace the water or just drain a little out the choice is yours, but you need to get the water below the height of the thermostat or it will all come pouring out till it finds its own level.

Remove the top radiator hose, and the smaller bypass hose. Remove the two bolts from either side of the water neck or housing and peel away from the engine block. It’s possible that you may need to give it a gentle tap to loosen it. Try not to dislodge any corrosion or debris back into the engine block. With the thermostat and the housing removed you will need to clean up the faces on the block and the housing (if refitting), this will allow a good seal with the new gasket.

The old thermostat I had was not only in back to front but a very unusual  design. This one worked by a twisting motion. I’m not convinced this was a correct part.


With the housing cleaned up as well as the block face it’s time to mount the thermostat. Make sure you replace the correct temperature thermostat actuation for your car.

Below I mention the use of an engine gasket sealer, this is not mandatory by any means, but it can make life a lot easier. It’s up to you if you wish to use the gasket sealer or not.


The new thermostat has a plate around the outside for fitting. Drill a small hole of 1/8 of an inch. This will allow any air to escape and avoid any air locks in the system.

At this point you can either use a new housing like I have, or use your existing housing. Clean up your housing on the inside to remove any sludge or rusted areas. Make sure you clean the old gasket of the faces completly and that the thermostat location recess lip is clean. If all is still ok, continue to use it. On the back of the housing that attaches to the engine there is a small recess as mentioned above, that will hold the thermostat in place to the block. Dry fit the housing to the block and make a note where the very top of the housing will be once secured back in place, either mark it or place a small piece of tape etc. The thermostat bolts are not horizontal for fitting so it may look to be in an odd location. Apply a very thin film of gasket sealer in the location recess. This will hold the thermostat in place during fitting and help avoid leaks. Make sure when fitting the thermostat pay attention to these two points. 1) Most importantly – the spring part of the housing fits into the engine block. 2) With the note and marking up you made earlier for the very top of the housing, make sure the hole you drilled earlier is located at that marked up top position. This will allow the air to be pushed through the hole and thus escape from the system. Allow the thermostat to set for a few minutes before fitting. If the gasket seal is to soft it will fall out anyway if you are not carefull.

The hole looks to be at the bottom here, that’s because it’s upside down to allow a good photo.

Next again apply a thin film of gasket seal around the back of the housing, the gasket itself will only fit one way. Gently press the the gasket into place and position around the holes.

Apply another very thin film of sealer over the gasket to help fill any pitted holes on the engine block that could allow a small leak. Next gently offer the thermostat housing up to the engine block, make sure you don’t knock it out of position. Insert the two bolts either side of the housing and nip them up finger tight. Apply a spanner and tighten fully. If you have used gasket seal, allow it it set for a while before adding the water/anti freeze mix.


At this point I replaced the water temperature sender switch as well. This is located at the rear of the distributor on the 289 block.  With the water drained down it could make sense to replace it for a small sum of £9 with a little piece of mind at the same time. Simply unscrew the small nut and washer and remove the wire to the dash gauge. Next undo the sender and remove. Replace the new water temperature sender into the manifold and tighten up. The water sender has a tapered thread so it will not sit fully down. You could also wrap a little PTFE tape around the thread for extra secure seal. Re-attach the water temperature wire and washer then tighten up the securing nut.

Lastly refit the two removed hoses and tighten the clips. Fill the radiator back up with water and anti freeze. Run the engine and make sure there are no air locks in the system. After a few minutes make sure the thermostat has opened and the water hoses are warm.


A real simple task that should take no more than half an hour tops. The car should warm up quicker thus being more efficient. Also the chrome looks great against the new paint job. You can complete two important jobs at the same time for a little amount of grief.

A well worth while job.

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One thought on “Water Thermostat Replacement

  1. Good Job, thanks for the effort to communicate the information.

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