Cooling issue.

[dougal9887]

Any thoughts on this issue would be appreciated.
The problem is one of generally running at a higher than usual temperature and overheating when the engine is stressed.
The engine was built in 2015, however the water pump was not replaced as it was said to have been fairly recent in the donor front cover. It looked and felt fine.
During 2016 and 2017 the cooling was fine under all conditions, including track days. If anything it seemed too efficient as the engine tended to struggle to get above 75deg on, for example, light motorway load. It never exceeded 85deg under any other conditions. The gauge reading was confirmed by the ECU reading.
Early in 2018 I noticed that, suddenly, it was generally running at 85deg and could reach 95deg on a motorway run. At Castle Combe 2018 it overheated after a few laps, expelling lots of coolant at about 110deg. I put some radweld in just in case a radiator leak had occurred, however this made no difference to subsequent runs, so continued with the day restricted to 3 laps then a cool down break. I drove back to Scotland at a steady 70mph with no further problems although the coolant temperature was around 90 deg. The car was fine for normal use the rest of the year, although running at the new higher 85deg. No water loss. No oil contamination.
For this year, the radiator was checked by a repair shop and the top seam resoldered, it was otherwise deemed fine. The hoses are 2015 and no leaks. I renewed the thermostat as a test although the existing one appeared to test fine.
This year I have exactly the same symptoms.
So under normal running conditions the cooling capacity appears to be at it's limit and any additional load results in overheating. I considered the possibility that the cooling system was being pressurised, pushing water out, then overheating, however further testing has proven this is not the case. The overheating occurs first, then water loss results. If the engine load is pushed up, the temperature rises, however if the load is immediately reduced it gradually cools and there is no water loss.
I am now of the opinion that poor circulation is the problem and that this can only result from a partial blockage or lack of pump pressure. Since the radiator, hoses and thermostat have all been checked and the block thoroughly cleaned before the 2015 build, and the change in running temperature in any case occurred abruptly, this only seems to leave the water pump as the culprit. There is no leak from the pump and it's rotation feels smooth.
So my question is, what could occur with the water pump that would result in a sudden loss of performance. Could the impeller be slipping on the shaft. Could the shaft have fractured. It seems too simple an assembly to fail (apart from bearings and seals)
Any ideas?
Dougal.

[David1953]

Well I have heard of hoses de-laminating, so an internal flap can block the flow. Looks normal on inspection and only happens under special conditions, like high flow rates.
Bit of a long shot.....

Good to talk to you yesterday.
David

[Craven]

Weak Mixture, ignition timing.

[rgh0]

A small slow cylinder head gasket leak can result in hot gases getting into the cooling water and leading to hot running or over heating without blowing out the water as the gas can disengage and come out through the radiator vent pipe rather than blowing out the water like a larger leak does

cheers
Rohan

[dougal9887]

Sorted.
It was the fan belt tension
In my defence, I had checked it a number of times and have always preferred to run it not too tight. This time I tried rotating the pulley which did so rather easily. I think the belt is slightly contaminated by oil from the unsealed dipstick. I tightened until I just couldn't rotate it and went for a test drive. Half hour on motorway at 70mph in fourth with stable 85deg, followed by spirited country road and best I could manage was 90deg. Cooled right back to 80deg on way back, so problem sorted.
I've paid for my mistake with 2 spoiled track days, lesson learned.
Just as well the Lotus Castle Combe day is such an enjoyable event without even going on track, enjoyed chatting to everyone.
Thanks for the responses.
Dougal.

[richardcox_lotus]

Interesting. My car often shows high temps, although without water loss. I too can turn the water pump pulley by hand. I?m still cautious on over-tightening the fan belt.

Any consensus on how tight it should be ?

[nigelrbfurness]

I'm with Rohan on this one. My money would be on a head gasket leak, probably no.4 cylinder into a corroded waterway in the head. I've seen this many times on twin cams with the symptoms exactly as you describe. It might not show up on a cold compression test so do it hot and watch the gauge for a few minutes.

Nigel F.

[dougal9887]

Well, the fan belt tension helped some but didn't cure the problem. Still running hotter than previously and overheats with sustained running above 3000rpm. A hot compression test showed an even 180psi and a leakdown test didn't appear to show anything unusual.
As the symptoms still suggested, to me, poor coolant circulation, I decided to whip the top off the radiator for a look inside. This is what I found

Blocked radiator.

Only 10 of the 56 columns worked properly, the remainder were either partially or completely blocked.
After 3 hours hard labour with bits of wire and steel strips it looked a lot better. Only one column was too solid to clear and I didn't want to damage it.

Columns cleaned out.

Got the top tank cleaned up and soldered it back on.

Radiator tank replaced.

I let the nice new paint job dry overnight and will replace it today and keep my fingers crossed! I don't know when it will next get tested in anger, however if I'm back to my normal, slightly low, 75deg running, I'll be optimistic!
At 46 years old, the radiator that is!, it was probably due a clean out, however I'll definitely be flushing out leak sealer asap if I ever need to use it again in an emergency as I suspect it is the real culprit here.
Dougal.

[69S4]

So do you live in a hard water area and use tap water in the cooling system (like me!)? Looking at what happens inside my kettle after a month or two maybe it's not surprising the radiator blocks up. If the radiator is marginal - like the small Elan one is - it wouldn't take much to reduce the cooling capacity to below adequate.

[William2]

As a general point the cooling abilities of the S4/Sprint radiator have always been a bit marginal, hence why so many owners have fitted full width alloy rads or the S3 version.

[dougal9887]

Soft water area, but agree it looks and feels very like limescale or such.
Can't say I'd found the cooling other than satisfactory, even a little enthusiastic until this problem.
Dougal.

[Grizzly]

I had a similar issue, basically sat in traffic or cruising at 30-60mph it was fine but if i was driving 'Spiritedly' the temp would get borderline excessive.

So after a bit of messing about turns out with the smaller rad fitted any holes round it letting air bypass has to be really well blocked off, the difference between mine starting to blow coolant out of the over flow pipe and not was the piece of foam that goes between the rad and the bonnet.