Water pump failure, head gasket may be gone, compressions 170/150/155/170

'93 NA6 with 96k miles. Heater was never hot in the 3 weeks of my ownership. Local garage failed to fix that. Car never overheated. Gauge always at 11.30 until it overheated in a split second and blew one second of hot air from the heater. No steam. I switched off and coasted to a halt. Let it cool down. Lifted the bonnet. No signs of anything having happened. No coolant anywhere.

Got the car to a nearby garage, who said, if:

  1. The heater wasn’t giving hot air and
  2. The temp gauge was ok and
  3. There is no pressure in the cooling system and
  4. You don’t have evidence of the service history, just the previous owner’s word
    then the water pump will be gone, and the car will have been cooling the engine only by thermo syphoning for weeks, months, or years.

Here’s the pump they took out. Lo and behold, no vanes left on the impeller side at all.

The compressions are 170/150/155/170.

Does this mean the head gasket is definitely gone, or could it be something else, or the head gasket AND other things? All advice appreciated, because it’ll help decide if I have the engine repaired, or if I replace it, even though the old one now has a new water pump and timing belt in it.

Btw, putting the new belt in and firing up caused every single hose to leak from both ends, and some in the middle, proving there had been no pressure in the system previously. This make me wonder how my local garage could have told me “Yes, of course Dave, the heater is now red hot”, because it wasn’t the next morning, and couldn’t possibly have been the previous day.

Since your going to have to fix any leaking cooling hoses anyway I would fix these first, if the engine is starting and running ok and cooling system works as it should you might just get away with it.

Having read your other post re the court issue etc, I get your concerns.
Based on the fact the pump should have vanes on it what has happened to them?
Did you have coolant in the system or just water.
Have they rusted away or broken off and blocked the water gallery somewhere.
My initial impression would be a blocked system.
Which I would be concerned about due to the fact the new pump was over pressuring the hoses and forcing them to leak.
IF it was my car I would be having a full strip down and flush and check for debris.
The works, engine, radiator, hoses the whole lot.
Before I fired it up again.
Just my opinion of course.

The repairing garage is 100% certain that there is no sign of the vanes having fallen off, but that they have corroded away because the coolant had not previously been changed often enough and had become acidic, or the system had been run with just water, or too high a concentration of water. The vanes had been turned into a sacrificial node, as is found in immersion heaters.

The seller had very recently put new coolant in, perhaps to disguise this defective maintenance.

The hoses were all on very loosely. They were not leaking before the overheat because the system was not under pressure before the overheat. As soon as the clamps were tightened, and a couple of hoses replaced, the hoses became water tight, even with the new pump actually providing pressure, for the first time in a long time.

The guys then spent another hour trying to bleed the system, and will have put a LOT of water through it, which will, I understand, have flushed anything untoward into the lowest part of the water gallery, from which it can’t escape (unless I tip the car up).

The garage that changed the water pump should be capable of doing a leakdown test which will pinpoint the problem. They should be able to do a rad pressure test as well.

I’ll leave you to crack on with it and the garage you have employed. Difficult to advise on what has/hasn’t been done. Might be like asking how long is a piece of string. :+1:

As luck would have it the nearest garage was only 2 minutes away as is an MX5 specialist.

Any water leaks internal or otherwise are easily found with the right equipment.
Also flushing and bleeding the system are different things, bleeding does not involve “putting a LOT of water through it” at all so you can rule that one out.

Hi Martin

Steep learning curve for me this.

How do they do a flush?

They used a pressure gauge to test for leaks. Is there anything else they should use?

It was in response to this “The guys then spent another hour trying to bleed the system, and will have put a LOT of water through it,”
I’m saying one is not the other. You wit’ me?

No, not with you.

Are you Martin Crabtree?

How come your previous post has disappeared?

I can see my posts are there.
Flushing is to try and clean out the system of small debris by rinsing it out with liquid.

Bleeding is to get the air out so it’s full with water and no air. When you refill a system after it’s been emptied air can get trapped in certain places. Air is compressible, water is not so it doesn’t work very well because it operates properly when the whole thing can be pressurised.
When you increase the pressure on water the boiling point goes up so it can continue doing its job at higher temps.
I don’t know anything about NAs, but most systems are self bleeding (eventually).

How do they do a flush?

They used a pressure gauge to test for leaks. Is there anything else they should use?

Have been trying to follow this over the various forums and threads, has a blown head gasket been confirmed and needing replaced? Or a complete engine needed?

I have no experience with NA but a flush can vary from in effectiveness from a refill, engine run and drain of the system at the minimum to a dismantling of the radiator, engine block, heater matrix and hoses allowing the components and galleries to be jetted out or back flushed with a hose pipe or high pressure wand.
Any scale, debris or sludge from a neglected system is likely to settle in the lowest parts of the radiator and heater cores reducing their effective area and sometimes a chemical pickle and flush with for example citric acid is required.