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Oil dash warning light


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What oil? when was it changed?

If decent oil (I am guessing this is when hot) it could be worn bearings on the crank or the pump (though I have no idea on TR7 pumps, I have never come across a badly worn ohv pump, nothing more than a few scratches)

Of course it could be the oil pressure switch playing up?

Think I would start with an oilchange and good oil, but dropping the sump and some new bearings and pump investigation would be on the cards in the very near future. On a warm, dry day.....

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First off, try another switch.  They can fail in this way.  Ideally beg, buy, borrow a pressure gauge so you can actually measure what is happening.  If pressure does really turn out to be low at hot idle but comes up quickly as revs increase then it could be considered as notice of required maintenance, provided there are no nasty noises.  If you've got any knocking/rumbling from the bottom end then stop driving it now.
Cold be a relief valve issue - broken spring maybe.  IIRC these can be accessed without major dismantling.  

Otherwise it's showing worn oil pump and/or crank/bearings and best to deal with this sooner rather than later.  As mentioned, Wynns or STP oil additives can treat the symptoms but should be regarded as a temporary measure.


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If the oil warning light is functioning as it should (that is a very BIG if) it should be switched of at around 3-5 lbf/in2.
If you have that kind of pressure your engine is fairly knackered, and you should hear some clear knocking noises when starting the engine.

A good starting point (after you have checked that your pressure switch is working properly) is to remove the oil pump,
and check the free length of the pressure relief spring, this should measure 43.18mm.
Also check the pump for extensive wear, and with that I really mean extensive. They can take a lot of damage before they really lose pressure.

You'll have to remove the clutch slave cylinder to get to the oil pump properly ...

As an afterthought, my Sprint engine when hot has a pressure on idle off ± 35-45 psi (2,5 - 3 Bar) with a maximum pressure of ±70 psi (5 Bar)
Engine has done over 100.000 km by now, and I have a mechanical Smith oil gauge (for what it's worth).

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I have had my OP light come on, but stay on at engine speeds greater than idle.  There were no knocking noises, it had good oil, but 107,000 miles.  Replacing the sensor got rid of the problem although max OP was about 30 PSI.

If your OP light goes out at speeds above idle it is unlikely to be the problem, although it may not be functioning correctly.  If I recall it is less than £10 and 20 mins to replace the sensor & clean up around it, so it is cheap to eliminate this as a cause.

The oil pump is easy to replace if you can get the car on a ramp, but you need to check that the OP drive engages into the hole in the bottom of the dizzy as you replace it.  As step 2 do what Theo suggests and take a decision whether to replace the oil pump.  I don't think that they are very expensive and on a ramp it takes less than 30 mins.

You have not given us many clues about the type of engine (is it a Rover or a TR7?)  its mileage, condition or history or if you have an OP gauge.  But before taking the engine apart try all other possibilities. I have found Slick 50 has not caused any ill effects on my TR7, Saab and Pugeot engines and has quietened them down a bit, but I would only use this as an expedient to minimise any further damage while you identify the real problem.

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