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Apropos the helpful tip about clogged radiators, do the condensers in air-conditioning cars not act as a screen for the coolant radiator which is of course, fitted behind the condensers and hence downstream of the airflow?

Two or three months ago I had an abrupt upward change in coolant temperature: 10 - 15 Degrees C and worryingly, up to 110 in motorway traffic jams. Checks of outward signs have been negative: fans operate, the radiator fins are clear and the water pump seems to be OK. Coolant is clean with little or no topping-up required.

The radiator was replaced three years/36000 miles ago because it was outwardly corroded. Internal galleries were clear.

Next stop is the thermostat. Has anyone had a stat failure? Replacement seems to be possible with a bit of wiggling of the connecting hoses and stat housing from under the plenum. I recall a recent posting that said it could be only a 15-minute job. Is that the case?

Motoring too and from work in Sheffield consists of a 15-minute journey when my usual 80 is held. That journey is probably not long enough for all relevant parts of the cooling system to be heat-soaked.

A long journey from Swansea to Sheffield today was particularly fraught because of several major jams. Clearly, cooling is not matching thermogenesis.

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I just picked up my car from the dealer having had a couple of new cats fitted. I have also replaced the turbo oil and coolant feeds/returns as these were badly corroded. One of the coolant returns split a couple of weeks ago and I replaced them both, followed by one of the oil feeds as that split aswell. I had the dealer do the others whilst it was in for the cats this week.

Cooling has improved dramatically. Returning from the dealer I queued for 40 minutes approaching the Forth Road Bridge in the mid day sun. From a normal running temperature of 80 it slowly climbed to just under 90, despite running the air con the whole time. There it stayed. Once clear of the queue it was back down to 80 within literally a few minutes. I've also noticed the fans seem to kick in sooner and stay on longer after stopping, although it has been very hot today (even for Scotland)

Prior to replacing these pipes, I would regularly see 100-110 in traffic and it would get there very quickly. So, perhaps over time these pipes can clog and compromise healthy circulation of coolant. Certainly the car is much happier.

BTW, the Larini hi-flo sports cats from PUK have transformed the car. Pick up is cleaner, it runs a lot smoother and has it definately gained a few BHP. It also sounds a lot frutier! I'm also wondering if they run cooler than the Lotus items, contributing to lower engine bay temperatures.

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Hi Mark,

That's a very interesting read. I have the exact same symptoms as you did. Car is running a bit hot and goes worse with air con on. Radiator looks in good condition and Iam reluctant to change it. How much did the other hoses cost as I will try this route first?

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Just back from a long run including lengthy queuing in traffic. Max temp was about 95 but it comes down very quickly once the fans kick in, a lot quicker than it used to. Running the air con does not have such a dramatic effect as it used to either. I'm reasonably convinced replacing the turbo coolant/oil pipes has had a positive effect on cooling.

So, from SJ, the 4 coolant pipes are

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Last Saturday I replaced the thermostat - in the boot, leaning over the engine, specs askew, blisteringly hot day, not good for 56-year-olds - went for a drive: no change. Besides, old thermostat seems to open at the right temperature and looks virtually new.

Flushed the rad from the rear with my Karcher - even the splashing didn't cool me down - marginal improvement. System bled at both points i.e. rad and just in front of thermostat housing. No air in the system. This isn't surprising because coolant losses are negligible.

Took the car into my local agents today - Gordon Lamb - for an air-clean of the radiator fins. Should be done at service intervals anyway. A drive over the peaks to the south of Sheffield took the temperature up to 100 but down hill back into Sheffield saw the temperature return to an indicated 80ish in minutes. Uphill it gets hot, downhill it cools. OK, but the difference is worryingly large.

I had the turbo coolant pipes replaced in February 2005 as part of rebuilt turbos job. The pipes were locally-made not Lotus but they should be OK. Yes, one hell of a job to get the old ones off - again at Gordon Lamb. I have little time for car mending and increasingly, less money. I'm going to check the pipes for kinks and hence possible interrupted flow.

So, cooling still not entirely convincing; I know it's particularly hot but . . . I have another motorway journey this coming Friday, Walsall, then again on Saturday: Maryport carnival and the annual Cockermouth Grammar School Maryport branch reunion. Those journeys should be testers.

Remote possibility - and it is outlandish: could the impeller have sheered/worked loose so that although the pully is driven, the impeller isn't moving? However, with the cap off the header tank, coolant seems to be circulating.

Any other possibilities?

Under the circumstances, watching the temperature gauge isn't good for blood pressure.

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have you replaced the radiator cap?

I had a similar problem but the other way getting cool down to 50 then back up to 90?

I did all the things you have but no change. I connected my ODBII software and the temp on that stayed steady at 90 the whole time so i rekon the gauge is faulty. change the sender for a new one and get some ODB software and run the car with that connected and see if it is actually getting hotter.

good luck


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Thanks Andy but OBD registers the same temperature as that on the gauge. Moreover, the air-con switches off at an indicated 110. These observations suggest that the sender and gauge are intact.

Close inspection of the turbo coolant pipes earlier this evening revealed a part-corroded and constricted elbow at the turbo end of the left hand inlet pipe. Mark's suggestion carries ever more weight.

If flow is restricted, coolant would back up and as the temperature sender is in the vicinity of the coolant outlet in the block, it will register the localised heat. The other three coolant pipes seem to be fine.

This is consistent with high temperature on load and reduced temperature on comparatively unloaded downhill running.

In February 2005 I had both turbos replaced and removal of the coolant pipes was a swine. Gordon Lamb managed to do the job without having to remove the engine but it was a close-run thing. All four pipes were replaced but as I recall, the left-hand inlet was repaired; it's turbo-end connection was retained.

Another repair is possible but I suspect that the entire pipe will have to me replaced. The feed pipes are particularly difficult to get at. I foresee more expense.

If I was to do the job myself - which 30 years or so ago would have been the case without a moment's thought - I would probably remove the engine mount and oil filter and housing, support the engine and leave the turbo on. There is room to attack the turbo-end coupling on the left hand side, the right-hand turbo is a different matter.

We shall see.

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Sounds like you found the cause.

It's a shame these hoses are such poor quality . I think Bobak got some braided ones made up , mine are all corroded along with the oil feeds.This winter i will replace them with some better quality ones.

let us know how you get on

cheers Andy

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Hi Andy, already asked him at the weekend. He has some pipes but not all to use as a template. These will be a lot cheaper as PNM will have them made as a whole flexible hose without the stiff metal section. Ti's this part which adds the cost onto the Lotus ones. should be about

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