“Blue” thermostat replacement S1 Elise

[richbk]

On Sunday evening after a glorious and spirited drive back through the Welsh mountains the dash temp gauge began to fluctuate at 67/68 then jump back to 87/88 then drop to 79/80 and has continued to do this after an evening left on the drive to rest . A bit of googling suggests the blue thermostat / sensor may be shot and needs replacing . 
the car is a 99 S1 Elise and despite a reasonable search I can’t find a definitive guide to how to change this part . I am hopeful it can be quickly removed and a new one fitted without the need to drain down the whole system and hopefully will only need under trays and wheel arch liners out . Or am I dreaming ? 

as ever , any advice gratefully received 

Richard / Ethan 

[Lithopsian]

Yes, replacement is as simple as unscrewing the old one and screwing in the new one.  You will get a little wet, just make sure you have the access you need and are ready to stick your thumb over the hole.  From beneath is best.  You should probably bleed the system afterwards, or at least keep a careful eye on the temperature the first time you drive it.

You might want to check for electrical gremlins first.  Erratic measurements are usually down to a loose connection or poor earth.  Failure of the sensor more commonly gives a consistent, but wrong, reading, perhaps slowly getting worse and eventually nothing at all.  This sensor is earthed through the engine and chassis straps, so check the earth straps.  The rear one is more exposed and likely to cause trouble.

One little thing to remember: there should be a sealing washer.  Apparently not essential, but seems like it would be more likely to leak without it.

Edited July 4, 2023 by Lithopsian

[richbk]

Many thanks .  Temp was flicking between 69/70 as a constant for last 5 miles of journey, then jumped up and down at usual temp , then back to the flicking quickly between 69/70 . 
will start with the thermostat and hope it’s a simple fix , not sure what the earth strap looks like, so will have a google . Car had just been into Oakmere lotus for new toelinks , could they have disturbed a strap ???

[Lithopsian]

Maybe.  The rear earth strap runs from the end of the gearbox casing to the chassis rail.  Easy to spot with the undertray off.  Just check that it hasn''t corroded through and is securely bolted on.  Wouldn't do any harm to take it off, have a good look, and clean up the contact surfaces.  Or it might just be the sender, they don't last forever.

[ethbk]

thank you , will do both. I assume the strap is just that, a metalic strap that runs to a fixing point on the chassis?

is the sender located from above or below the engine?

I am reading different things, some say near water bottle on pax side, other underneath ? am i reading s1 and s2 stuff just to confuse myself? Its the sensor i am looking to replace 1st i guess, then if that doesnt work i guess its the thermostrat after ? 

 

Edited July 4, 2023 by ethbk

[Lithopsian]

The earth strap is a moderately thick black cable with ring terminals on either end.  Different sizes!  M8 at the chassis end and M10 (fine thread!) at the gearbox.  The connection to the chassis is a bolt into a rivnut, probably seized because the end of the bolt is exposed and will be rusty.  Luckily you can get to the back of the rivnut to clean the bolt threads, grip the rivnut to stop it turning, and as a last resort just cut the whole lot off.  There is a special cupped washer that fits over the raised lip of the rivnut to make electrical contact with the chassis.  The chassis is anodised and the contact patch should have been sanded down, but won't hurt to do it again.  The gearbox end is just a bolt into the gearbox, doesn't seem to corrode too much.

The sender location is the same on all the Rover engines, S1 or S2, but the sender itself is different.  The S2 doesn't use a separate sender for the Stack and ECU.  Anyway, it is easily visible with the boot lid open, between the coolant tank and the engine, towards the front of the car.  Not so easily accessible; it is on an elbow of the engine outlet, with the brown ECU sender sticking out horizontally and the blue Stack sender sticking vertically down.  So replacing the blue sender from above is not easy.  Access through the wheel arch is possible, but it is a stretch and there are things in the way.  Access from underneath is best, just take off the undertray, preferably with the car lifted a little.

Pray you don't have to replace the thermostat, much harder to get at, wedged between the engine and the boot divider, under the inlet manifold.  Unless you have a modified setup for something like a PRRT which would be located somewhere close to the two temperature senders.

[Martin R]

Rich if the sensor does not fix it try the following. Take it for a spirited drive. Let it cool down for about 2 hours. Slowly remove coolant cap. Is there a lot of hissing and or water rushing back into the coolant bottle? If there is it may well be a blow across the fire ring causing excess pressure in the system. The temp dodging about is the coolant cap releasing the excess pressure and then resealing. If there is only a slight hiss after 2 hours or so all should be well. I drove mine home from a LeMans trackday with the same symptoms after trying 2 or 3 different caps? Try changing the cap as well. Mine had an indent on the hot side of the head by the exhaust valves. lets hope its something more simple.

[ethbk]

Hi folks. New sensor arrived, wrists greased and bent in ungodly directions to remove. dads fingers covered hole, new sensor with fresh ptfe tape inserted. lost about 1/4 cup of coolant. ran with cap off for 10-15 mins on drive and then took for a drive and hey presto - a steady 85. 

all seems well, except i have spied a slight weep on the cam seal . possibly cause of sensor fail as it appears to be gentling dropping right on to the top of the sensor......another job for another day.

Thanks for all the advice

ethan