Cooling system problem ? / Waterpump ?

Date: Fri, 14 Aug 1998 10:32:30 +0100 (WET DST)
From: Richard Candler
Subject: Imp problems


I have recently bought a Mark 2 Imp ('68). Largely due to my mate Dave (Edge) who has a '69 Stiletto and half a bottle of vodka each.
It had been stored in a garage for 18 years, and wasn't running so I got it for 150 quid. Anyway, I got it on June 10th, and by the 22nd it was on the road. Hurrah!
However, I think I have a problem with the cooling system, somewhere and am not sure. What I really need is some advice. The oil pressure/water overheating light (one and the same on my car), comes on dimly very early, and stays on almost all the time.
after much persuasion (and a few goes with the jetwash) I have cleared all the cooling hoses so the the front heater warms up. However, I am worried about the water pump. I assumed that if it was working I could clamp a pipe, with my fingers, rev the engine and feel the pressure. When I do this, nothing happens. Feels like the pipes are full of air. Which I know they're not. All the pipes, but I can't feel any pressure. There are no coolant leaks. DOES THIS SOUND LIKE A FAULTY WATER PUMP? ANYONE? I thought some advice would be worth it before going out and buying one. And one more question, if I fit an oil cooler, do I need to upgrade the oil pump to cope or not?



PS. Sorry about the essay!

Date: Fri, 14 Aug 1998 11:47:16 +0100 (WET DST)
From: Simon Trickett
Subject: RE: Imp problems

Having worked as a fitter for a water company I can offer this advice !!

The Imp pump is not a constant displacement pump (centrifugal) so if you squeeze the pipe will probs not feel a pressure build up, if it was a constant displacement pump (such as a reciprocating piston pump) you would feel a great pressure build up as the fluid can not escape anywhere.

But of cause its an imp pump ..........get it change + all pipes try Malcolm A of Speedies

Ps well done for a fast Imp must of be stored well!!

see yer

Simon Trickett

Date: Fri, 14 Aug 1998 12:18:43 +0100 (WET DST)
From: Gary and Carol Henderson
Subject: RE: Imp problems

Hi Richard

If the water-pump doesn't leak out either of the bearing weep-holes, it's fine! Its only a simple centrifugal circulation pump; not a postive-displacement type (all cars have similar ones.) If you clamp a pipe, the bypass hoses will take the diverted flow with little pressure rise.

When ignition first turned on, does the oil light come on brightly, then extinguish as soon as the engine starts? If not, most likely the oil-pressure switch has got bored with sitting in a shed for so long.

Good luck


Date: Fri, 14 Aug 1998 12:55:37 +0100 (WET DST)
From: Mark Norman
Subject: RE: Imp problems

>If the water-pump doesn't leak out either of the bearing weep-holes, it's fine!

I have heard stories of pumps that have been so old their fins have worn away in the water. Probably not imp ones though!

Date: Fri, 14 Aug 1998 12:18:57 +0100 (WET DST)
From: Gary and Carol Henderson
Subject: RE: Imp problems

I still say if it doesn't leak and/or make terrible noises, leave it be! It might be of the 'good' vintage circa 1970 - much better than the late Q-H replacements which looked the same outside but had no water-grooves inside. GaryH

Date: Fri, 14 Aug 1998 12:40:46 +0100 (WET DST)
From: Mark Norman
Subject: Re: Imp problems

>The oil pressure/water overheating light (one and the same on
>my car), comes on dimly very early, and stays on almost all the time.

Do you think the engine is actually overheating at all? I.e is it getting lumpy, behaving strangely or whatever? That fault could well be simply an electrical problem.
I'd suggest fitting a spare/borrowed temp gauge & sender & checking what temperature the engine gets to while it's running before spending any money. Also once the light does come on dimly, disconnect each sender in turn just to check it's not an oil pressure problem, or have you already done that?
If it isn't overheating, new switches are a lot cheaper than water pumps!
(Or just keep the temp gauge)

You certainly won't be able to feel any pressure in the pipes by squeezing their sides. I guess you could get some idea of how well the water is circulating by how hot the long pipes down the car get once the engine has warmed up - my car has new pipes now & you wouldn't be able to comfortably hold them in your hand for very long. If they are getting hot, then something must be pushing the water down them.
Unblocking the airways (easiest with a steam/high pressure water cleaner) in the radiator can do wonders for cooling, also descaling it if the car has been in a hard water area or has been run without antifreeze.

So far as I know there is no need to change the oil pump, I think all normal production Imps, ie. non modified, had the same type of oil pump irrespective of what engine they had or whether they had oil coolers. Certainly I'm planning on fitting an oil cooler without upgrading the pump, though you may need to do something if you are thinking of fitting the cooler at the front of the car or anything odd like that!
- does anyone else have any comments?

Date: Fri, 14 Aug 1998 09:24:28 -0400 (EDT)
From: Roger W.Swift
Subject: Re: Imp problems

Sounds like the old cherry to me - gauge sender unit instead of light switch - does the light get brighter as the engine warms up?
Alternatively the switch could be faulty.
My MK2 from New Zealand started to show a light soon after leaving the National in Scotland but was obviously not overheating or losing water so I disconnected the sender unit and carried on knowing that a light would mean low oil pressure. 600 miles later at indicated motorway speeds up to 80+ it is still ok.
(Perhaps it's something to do with the thermometer kit I bought at National and intend to fit soon)


Date: Fri, 14 Aug 1998 16:37:51 +0100 (WET DST)
From: Richard Candler
Subject: Re: Imp problems

> gauge sender unit instead of light
> switch - does the light get brighter as the engine warms up?
> Alternatively the switch could be faulty.

Yes, the light does get brighter, but hasn't (yet) got as bright as it is when I first turn the key in the ignition. This was my other guess.
That some-one in the past had fitted a sender unit but wired it to the light. Was this a common thing to do? I actually have a temp gauge from a later Mk2 (some-one in a Fiesta stopped me and gave me a host of freebies from the remains of an Imp he was taking to Imp heaven).
I assume all I need to do is run an earth from another dashboard unit (fuel gauge?), and disconnect the sender from it's original circuit and instead run a wire from there to the temp gauge. The engine's certainly not overheating ( well, the rad. cap doesn't blow!).
Problem is I don't know how to tell if I've got a faulty switch there or a sender unit. I have a replacement temp. switch, and it doesn't look much like what's in the hole at the moment (which after 30 years is stuck in there pretty well!). Can you tell the difference just by looking? The last thing I want to do is wire a temp gauge to a faulty switch, thinking that it's a sender and overheat the engine.

Date: Fri, 14 Aug 1998 17:20:18 +0100 (WET DST)
From: Mark Norman
Subject: Re: Imp problems

>Problem is I don't know how to tell if I've got a faulty switch there or a
>sender unit.

I'd replace it anyway if I were you - a sender unit is only a couple of quid, and who knows what a 30 year old one will be like. Someone (can't remember who - sorry) was telling me that the only sender units that truly match the gauges are Smith's ones - any other will give a false reading. Don't know how true that is.


Date: Fri, 14 Aug 1998 17:58:54 +0100 (WET DST)
From: Carsten
Subject: Re: Imp problems

Hi there,
here are my experience:
I had a similar problem: smith instrument (analogue) not working in imp sport engine. I tried two sensors, but it got no better. I tried to repair the instrument, but that was 20 years old and rusty as it could.
So, i decided to go for a new one. And I bought a mini combination.
Instrument is manufactured by carbont automotive (who are on the web, they have a site running with photos of their products, but they don't answer e-mail :-( ), and the mini sender unit. the sensor fits into the imp thermostat housing hole, but only with great care, as its shape is a bit different on its lower end. It will fit, and no water leaks if 'handy' drawn into. it worked first time, although i don't have any voltage stabilizer fitted (the instrument tells me to have 10 Volts, I have 12,5 or so, but who cares?).
A method to find your fault should be:
1. take an ohmmeter and a watercooker. put the sensor in the cooker, cook it, and measure it's resistance all the time. there MUST be a point , some 80°, i think, when it switches. You could also use wires and a lamp and 12 volts to build up a wiring situation where the light will work when the switch closes due to the cooking water getting hot. Nice method to check the switching temp of a suspect switch, too.
2. the instrument: most sensors come from 1kohm to zero. you could find a potentiometer, linear, 0-1 kohm, and built a wiring that includes the 12 volt-source, the poti and the instrument in one line. if you now turn the poti up, the instrument should come up, too, as the voltage in the instrument increases/decreases. Nice method to find out wethere a specific sensor fits a specific instrument.
another tip for a new sensor, if it does not fit at all, is to go for a t-shaped piece of water pipe, made from metal. cut a water hose that is always in use (even in cold state: the one that leaves the thermosthat housing to the right, e.g.), and fitt the t-piece. in the t-part itself, make a fitting for the new sensor. cable it appropriately to the new instrument, that's all. nice if no original sensor could be found or no instrument is available for the car.
Greets from germany,


(whose Centaur now has a real working water temp system using a smith analogue instrument, black/white hanging needle.). was expensive, costs me approx 60 US-dollar/104 DM. But the old smithie was dead.
BTW: I now have two unuseable but hopefully sensors here.... one is brand new !

they are for imp sport.

Date: Sat, 15 Aug 1998 08:59:40 +0100 (WET DST)
From: Adrian Saville
Subject: Re: Imp Problems

    Turn on ignition
  1. Gauge will come on brightly to indicate low oil pressure
    Engine now running
  2. If a temperature switch is fitted light will extinguish once oil is up to pressure
  3. If temperature guage sender is fitted light will glow dimly then gradually build until a stable temperature is reached
  4. If oil gauge sender is fitted light will increase / decrease in brightness dependent on engine revs