S2 4.2 Cooling

[robertmurrell]

Hello,
I have a problem with my E.
The engine has been rebuilt, all the cooling jackets were flushed and cleaned by me so I know they are clean, the head is very clean inside.
It has a new water pump, the timing is fine, it has a new thermostat, it has new leads, plugs and electronic ignition with new distributor
It has newer type fans on the radiator not them crappy originals.
The car runs fine (and on keeps cool when pushed hard) even when on a very hot day as I have had in Europe recently, but when in slow moving city traffic it gets very hot, like near the red hot. The fans work.
The only thing I have not done is change the radiator, but it does look clean inside from what I can see.
Would a new aluminium type stop this, or do I just have to avoid town traffic.
What I do notice is that oil pressured drops too at low revs when it gets CITY hot so the engine is actually very hot and not just the temp gauge.

[DWW]

I would check whether the fan is pulling cold air in rather than pushing hot air out the front, in which case the polarity of the fan wires needs reversing.

[chrisfell]

As Danny said, I had just this problem and it was that the fan was wired to push rather than pull air through the radiator. At a standstill it worked, but driving slowly in traffic the air coming through the nose stopped the fan pushing enough air through the radiator to cool the engine.

Simple to check, also simple to correct.

[malcolm]

When you say oil pressure drops, how low do you mean?

[mgcjag]

What fans are you useing....in front of the radiator or between radiator and engine...the later is the way to go with a correct cowl fitted to the radiator..
Steve

[MSM]

The fact that you say it keeps cool when pushed hard eliminates the radiator as a problem.

As has been suggested already check the airflow direction, if the fans are on the engine side of the radiator, where they should be, see if a piece of paper stcks to the radiator air inlet face when the fans are running. That shows the fans are sucking.

How does the cooling perform if you leave the car ticking over on your drive? If the fans cycle on and off when it gets hot that is what should happen but it sounds as if it does not happen in city traffic which could indicate wrong airflow direction.

Report back.

[paydase]

Electric oil pressure gauges can become faulty.
Check your oil pressure with a mechanical gauge

[MarekH]

This sounds like a similar argument often heard with the v12:- cooling is fine so long as you have plenty of water flow and airflow, but becomes marginal in stop-go traffic. This is because although heat generation is much lower when idling, heat dissipation is even lower.

The temperature you see is simply the balancing item between heat generated and heat dissipated. When rpm is low, the water pump isn't circulating much coolant and without airflow, the radiator may not keep up, even though it has a much easier task than under heavy load at speed.

The primary culprit with the v12 is the thermostat. This has to not only open up the path to the radiator, but it also has to close off the path to bypass. If the thermostat doesn't extend open far enough, the bypass route for the water remains partially open and that means a fair proportion of the hot water simply recirculates back into the engine block rather than takes the longer and more difficult path to the radiator. Temperature inevitably creeps up.

Since you have checked off most of the usual suspects, pull the top of the thermostat housing open, check the thermostat housing depth and verify that your thermostat opens up and extends its lower (spring loaded) foot at least that far when in a pan of boiling water. Failure to seal off the bypass and divert all of the water into the radiator means you never enable the radiator's full cooling capacity. This only becomes noticeable when water flow is at a minimum.

You should also verify that your Otter switch comes on and turns off at a temperature consistent with the temperature rating of the thermostat being used, given the Otter's location.

kind regards
Marek