Practically Classics Forum

I have owned my Rover P6 3500 for several years but over the last 5 years have suffered from high under bonnet temps down to the higher temps that the modern unleaded fuels burn at - this has not quite got to an overheating situation - more that the under bonnet temp got so high (temp guage just out of the red) that the car would stall due to fuel vaperisation. The car was always fine when it was moving - but on a summers days in standing traffic I stood no chance - bring the revs on the engine up to get the water round the rad and the fan to draw air just put the needle in to the red and the car stalling.

With only 20k on the clock and the car being one of the most original examples out there (never welded / painted) - I did not want to do the obvious and bolt an electric fan to it. In the end it has been a combination of several things in order to find the cure - the engine otherwise is in good health / tune etc. The block was flushed and the radiator recored with with a high flow matrix along with new hoses / thermostat / rad cap etc (you can not tell the difference from the original rad matrix) this helped a little but not enough - next off came the the exhaust manifolds which were blasted and ceramic coated (nearly £400) this again improved matters but not enough. Over the last day I fitted a high volume water pump from JR Wadams - (no difference in original appearance) - now I can let the car stand but when the temp gets high in standing traffic - if I bring the revs up the pump gets to work and down comes the temp. Unsure if I had have done the pump first if just this on it's own would have done the trick - somehow I am not sure it would have - I am just happy that the cure could be found - however - it has come at quite some cost - still far cheaper than an engine rebuild!

Great to hear that you got it sorted.
Posts like this are very useful I find. Folks (including me) are usually posting questions rather than answers, so its super to read about the effective solution to an issue which so many people encounter.

Thanks Grumpy!

Good to see a fix. what condition was the origional pump in?

Hi GN

As a fellow P6 V8 driver it's good to hear when people solve these little problems.

My car had never suffered from the dreaded vapour lock until I cleaned the oil off the block last year. I think the years of oil and road grime had formed a thermal insulation barrier between the block and the fuel pipe and when I cleaned it off the first time it got hot the engine died

I've also fitted a recored (triple) rad and flushed everything backwards, forwards and sideways to ensure it's all clean. The usual suspect tends to be the inlet manifold tower which can become clogged up too and that is all clean. I agree that reducing the under bonnet temp is the way to go and I wondered if you had the stock cast iron manifolds on your car? I'd heard that coating cast iron manifolds would lead to early failure due to thermal shock as the heat generated by the exhaust gases has nowhere to radiate to??? Unless you've had them coated inside too, but would that not reduce flow??? Theoretically it should help fuel consumption and performance too as the temperature of the air into the cleaner box should be reduced. Be interesting to hear if this is the case.

I fitted an electric fan to mine and removed the engine driven fan to help fuel economy, but I couldn't get a fan sufficiently powerful enough to shift enough air through the rad when stationary. There's not a lot of space on either the front or back of the V8 rad, even less with the 3 row core. That works fine in the winter months but now it's warming up a bit I've refitted the engine driven fan and the temp remains very stable with that. The high flow water pump is a good idea too.

Dave

TerryG wrote:

Good to see a fix. what condition was the original pump in?

The pump was mint when I got it off - no obvious wear and the impeller looks like new - the difference with the high volume pump being that the impeller has twice the amount of vanes fitted although it is of the same diameter of the original.

Dave3066 wrote:

I wondered if you had the stock cast iron manifolds on your car? I'd heard that coating cast iron manifolds would lead to early failure due to thermal shock as the heat generated by the exhaust gases has nowhere to radiate to??? Unless you've had them coated inside too, but would that not reduce flow??

The exhaust manifolds are the original cast iron ones - Only the external faces have been treated - I have not heard of any issues with early failure through thermal shock to manifolds - however the temperature of the gases transferred onwards to the remaining exhaust system are higher has a direct result of the ceramic coating and I have heard of owners suffering from the front downpipes (mild steel) having a short lifespan - I have a stainless system fitted - all I can do is monitor it and see how it gets on.

I fitted one of those to my P5B afew years ago, and although the car has done less than 1000 miles since, the bearing collapsed a few weeks ago, luckily when the car was idling at home. Now I'm unsure whether to replace it with another one, or get one from a different source altogether.

Don't start me on JRWs supposed high volume pumps

Surely a greater number of vanes means a greater likelihood of cavitation at speed?
Or are the Dolly Sprint racers in Australia (where it apparently gets warm during the race season) just lucky to get away with changing their 12 vane water pumps for 6 vane ones?

I work in an environmental / construction industry allied trade, on occasions I need to pump huge volumes of water - quickly - so I tend to know a few things about pumps - the main point being is provided the pitch and angle of the pump vanes is correct to the speed of the impeller it should do the job but quite odd laws apply some times as stated in JPB's post where less vanes gives a better output by reducing cavitation and in other cases the reverse of this applies where the pump speed becomes critical. I am more than happy with the present set up on the car - as at least I can now control the under bonnet temperatures and use the car in decent weather.