Running hot - can the water pump be the cause?

Sorry for the long message but this one is a total mystery to me so I'll open it up to discussion!

About 6 years ago one of the small oil cooler hoses on my GTA Turbo suddenly split causing a pin hole in the rubber and quickly emptying the coolant as I was driving along. Luckily I noticed the temp gauge rising rapidly and quickly pulled over to the side of the road, switching the engine off before the gauge entered the read. The offending hose was 'adjusted' by the RAC and replaced the same week.

However since that point the car has always ran hotter than previous. In hot conditions and when driving up a hill the gauge will go well beyond the 90 mark and can get close to the start of the red.

Over the years I've had various items replaced in an attempt to cure this:

Temp sender
Temp (+ oil pressure etc) gauge
Thermostat
Radiator fan
New radiator with air ducting
Head gaskets replaced and water channels cleaned of scale and silt.

The last two were effective but still not back to its original self. The coolant level needs to keep being topped up and hence the circuit must be leaking from somewhere yet it still pressurises properly.

Since the problem seems to be getting worse I can only assume that whilst all the above have helped they've still not got to the root of the problem. Looking at the area around the water pump and thermostat housing there seems to be deposits of crystallised coolant but no visible signs of a leak.

All I can think is that the water pump is worn and is leaking from somewhere and the impeller blades have eroded so they are no longer effective in pushing the water fast enough. (I've read that the pump can be damaged if it runs without coolant)

Any ideas anyone. Its all I can think of since it seems to be the last element in the system......

The blades of the pump cant be worn as they dont touch anything in the first place to get that worn, and if its still connected it must still be spinning at the same speed.

The only other option is a porous head, and with a increase in pressure due to combustion, then its going to raise the running temperature

I recently had a leak that was virtually undetectable by visual inspection. I was losing coolant into the `vee` somewhere around the water pump area.
After a lot of checking with the engine running I found that the leak was actually coming from the water pump end casing.
After removing the water pump and stripping it down I found that the impellor blades were ok but erosion of the water pump casing was so great that it had eventually worn through and was so wafer thin that the coolant just seeped through with no apparent leakage `hole`. This was one underperforming pump as the impellor to casing clearance was so large that the pump performance would be greatly impaired.
Being a cheapskate I welded up the casing, machined flat the sealing face,as it should have been, and reassembled. Job done ok. This was on an engine with 87k miles.Its done 4k since and the coolant temp is as at should be.
Something to bear in mind as another possibility.

Also check that the radiator has been properly bled of air... the inlet and outlet pipes are both set halfway up the rad so the air gets trapped in the top half. there is a rubber bleed off pipe on the top corner, driver's side which you can reach from underneath...
Or is this too obvious?

Just remembered. There is also a small hole (2 -3mm) in the water pump shaft casing. If you can see this ( from the underside probably with a torch and inspection mirror) and you notice any crystalised coolant or evidence of a leak is present you will probably find that the water pump shaft mechanical seal has broken down and is allowing coolant past the impellor, along the shaft and out through the `tell-tale` hole.If this is the case look for a replacement pump as this seal to replace will probably be more than half the cost of a new pump.

Stevie,

I can't spot any play in the shaft and last time I got Paul Sage to look there was no seepage through the 'weep hole'.

If the impeller or casing is eroded or worn then I'm wondering if the pump is cavitating (churning the water but not moving it too much) - with the exception of the main pipes it is the only part of the cooling system not to have been overhauled.

When you replaced the head gaskets, did the old ones seem to be ok? Im thinking its a head problem, which built up pressure and caused the split hose in the first place. Did you have the heads resurfaced and pressure checked when you done the gaskets?

Unfortunately I can`t give you a precise `before and after` judgement on my cars running temperature. I didn`t have any perceived cooling problems even after I found this constant small leak that got increasingly worse. However, from memory, the temp. gauge would read somewhere around the 80 - 85 deg mark and if stuck in town traffic often would go over 90 then the fan would cut in. Since fixing the leak and the pump the temp. gauge is now reading on average some 10 degrees lower even in the warmer weather we have been having lately, and in the same driving conditions that I usually see I haven`t had the temp. gauge go over the 90 mark (the driving environment in our area means that it is the exception rather than the rule to get stuck in traffic jams-unless you visit the Lake District on a summer Bank Holiday which most locals don`t do!).
As for your cavitation theory, yes you are correct, erosion of the impellor (which does happen to some degree) and erosion of the casing (which from my experience was much worse), will give cause to cavitation and therefore hamper circulation of the coolant. Pumps are tolerant of a fair amount or wear but once this gets excessive performance drops right off.
Looks like its time to change your pump - or get it repaired. But first check that the system has been bled as Rupert posted.

traffic jams..... poor old Darren spends a lot of time queueing to get into Guildford in the mornings.... the roadworks'll be finished soon mate!

David,

A 'litmus style' test was run on the coolant to check for dissolved CO2 & CO in the water prior to removing the heads. This showed absolutely no traces of any exhaust gases so it was very unlikely that they were leaking anyway.

To be honest I had the heads done to make sure and it was also a chance to give them a general overhaul. The gaskets and heads showed no signs of any water leaks though and were not warped at all. The other main advantage was that the liners could be clamped and the scale was cleaned out from the water ways.

You could try checking theres no leaks on the water feed to to the turbo (if it is water cooled!) Any leak would be evaporated off instantly.

What is the expected running temperature during normal conditions, i.e. sunny day doing say 60 MPH ?
Mine seems to sit halfway between 50 & 90 degrees.
If I'm stationary for any length of time it tips over 90 at which point I turn the heater on to try to dissipate some of the heat.

Don`t know what the correct running temp should be but mine shows the same during normal running at halfway between the 50 - 90, say 70 degrees. If it goes above 90 after a long time in standing traffic the fan kicks in and down it goes to `normal` again regardless of heater position.
Maybe the new radiator I just fitted helps.

Optimum has to be at least 82 degrees. This is the temperature the ECU converts to the proper mapped tables for fueling and ignition, with no additional enrichment or ignition retard.

I have a persistent coolant problem.

The coolant level in the expansion tank fluctuates up and down, and I often check it to find coolant stains on the outside of the expansion tank where the coolant has forced itself out past the cap.

I've recently fitted a new radiator (the old one had a hole in it caused by the fan rubbing against it!) and all the hoses have been replaced in the past. I,ve only ever been able to bleed the system from the bleed screw in the thermostat casing on top of the water pump and no air comes out here. However, the the bleed pipe on the side of the radiator appears to be blocked and I,ve never been able to bleed it here. Nothing comes out even when I completely unscrew it. I am askng a silly question, but could this be my problem? Is it critical that I am also able to bleed the system here?

Also, on the back of the water pump, there is a small rubber hose which protrudes out but which goes nowhere. It's simply blocked at the end with a plastic bung. Does any one know what purpose this serves? I've replaced this with a new hose because the original slpit and was leaking coolant into the 'v'. But because this is in a quite in-accessible place (it juts out into the 'v' under the inlet manifold), it's difficult to tell whether I've replaced it properly and it's not still leaking! (I replaced it without removing the inlet manifold - very tricky!)

How difficult is it to remove the water pump? Can it be done with the engine in-situ?

And finally, could a sticking thermostat be the problem?

Apologies for the long post! Thanks for reading and I appreciate any help. Thanks.