Strange Engine Sound?


I’m now experiencng my first issue with my new 5(91 1.6 Eunos). To begin with, at low revs and on start up, it was a whirring noise not present higher up. Now its at tick over and when reving. I thought it might be the belt around the power steering and air conditioning so i tried tightening it with no joy. Its perhaps a little more central and more of a screatch with the bonnet up. 

One thing i have noticed is that the top pipe on the radiator was collapsed (vacumn had formed in it) and removing the radiator cap allowed it to reform. I dont know if this is connected but worth mentioning. 


Does the whirring noise change or go away when you press the clutch pedal?

Try the stethoscope approach - length of garden hose, put one end near ear, put other end around various bits of engine bay while engine is runnng, identify source of noise. But don’t go chopping your fingers off on anything!

 Waterump noise/leak ???

There is a fairly quiet whirring noise that goes away when the clutch is pressed, that’s separate to this issue (incidentally, what would that be??). This noise is a screeching noise that increases with engine revs. As I said, the radiator top hose was sucked flat, I had to remove the radiator cap to allow it to reform. Really hoping I’ve not bought a lemon. It’s got tones of mx5 owners club stuff such as a tax disc holder. Perhaps I can find the car on here. 

Agree with waterpump suggestion especially if the belts are sound. They are a component which people tend to change “whether it needs it or not” during a cambelt renewal.

Wonder if the radiator is blocked with sludge too? Sounds to me coolant has boiled off and creating a vacuum as it cools. Either way, I’d personally not go any great distance with it for now.

If the cap is blocked on the rad creating a vacuum, would this be enough to starv the pump?

I’ve videod the sound and posted it here, you can here it a short way into the video. As you can see, temps are fine, bottle is good etc.

That screech has to be the water pump .

 It setainly sounds like it, rather than a drive belt, however it does seem to come and go almost as if something is touching something else as the engine rocks on its mountings while slowing down. I would look for water leaks under the pump (see if there is a steady drip while the engine is idling/water stains et.)  and also do the stethoscope test just to be sure.

Does the water pump tension the cambelt on these cars? If so work quickly to avoid potential disaster!

I left the car in the garage over night and no sign of leakage. I don’t think the pump tensions the belt, anybody know for sure??

I removed the aircon/power steering pump belt to make sure it wasn’t that. Looking through Haynes, it’s a little bit of work.


Right, I’ve replaced the pump for a nice shiny new one and the noise is still there!!! What else could it be?

So, just wanted to add, I noticed the alternoator/water pump belt is toothed for some reason?  There are no teeth on the pulleys and the belts don’t have teeth.

Hmm, list of possible options:

Alternator bearing? (Have you revved it with the belt off?)

Power steering pump bearing?

You’ve done the water pump so that’s what’s left.

HTH, tom.

agree with Tom definatly sounds like a bearing rather than a belt .

And check both end bearings , the rear is usually a brass/bronze bush that can and do wear with time allowing the rotor to float.

Hi there,

what are end bearings?

 My car mk1 91 vintage has a real screech when I start it up after a week of inactivity but if I start it up the next day it is not there. Water pump was changed when belts were done around 2500 miles ago and belts are all good tension wise.

I think this is something my repairer will have to investigate for me.

ok in simple terms , the alternator has a rod through the middle that has a pulley on one end (the bit you see) and a commutator on the other , its basically an eneltric motor( basically ). this rod has to be kept in place and its done so by bearings either roller/ ball bearing races or a brazz/bronze bush , if thses wear the rod is able to ‘‘wobble’’  .

One way to track down where your fault is or at least eliminate a few options is run the engine without the drive belts (not timing belt)

Someone from Mazda Menders may be able to confirm this wouldnt do any harm (not 100% on MX5 surgury yet)


Oh right, the bearings for the alternator. No it’s not those, the noise isn’t coming from there. Thanks for your help though. 

 Took mine in to my local man re the screetch, it would seem that my auxilary belts are in poor condition and need changing, also the fact that the car is not used that much does not help apparently. Belts are being changed in the next few days.

1 water pump, 1 cam belt, and a thermostat later, it turned out to be the alternator belt. Oh well. Lots of work I don’t have to worry about bow anyway :slight_smile: I can do the belts in my sleep now.