Conquest Drophead overheating

David Williamson
Posts: 3
Joined: Mon Feb 15, 2016 10:41 am

Conquest Drophead overheating

Post by David Williamson » Tue Nov 28, 2017 8:53 pm

Hi,
My Conquest Drophead usually runs very reliably and has only shown a slight increase in water temperature after a long period in very slow traffic. However, last summer, I was stuck in very slow traffic after a major show. The car gradually warmed up to a little over 190F and started to show the slightly rough tickover that usually comes with slight overheating. Normally the car would cool down again when I get moving but on this occasion, the temperature stayed high until I got home in spite of around 30 miles of clear road at 50 - 60 mph. Going faster or slower appeared to have no impact on the temperature. The car has been fine since then, warming up slightly on steep hills and cooling down again immediately thereafter. I am keen to avoid this overheating happening again when the weather gets warmer and would be interested in any views on what could have caused this. The system has been flushed and showed very little corrosion and little dirty water. It has new antifreeze and the overall coolant level stays steady at around 1/2" below the bottom of the filler neck even after getting hot. Someone has suggested the water pump may be to blame. I believe Conquest Century engines seldom overheat so I would appreciate a few thought on what I should check.

Thanks
David

simonp
Posts: 322
Joined: Mon Mar 07, 2016 9:59 am
Location: Birmingham

Re: Conquest Drophead overheating

Post by simonp » Tue Nov 28, 2017 9:37 pm

Hi David

I recently had similar problems with my SP250 and we similarly changed the water pump with no inprovement. I was suspecting a head gasket problem as had no previous problems with the radiator.

If fact it was the radiator which was about 25% blocked. It was last recored over 20 years ago. It has now been recored again which has made a huge difference and it now runs too cool.

SimonP
Daimler SP 250 - "To feel its eager response as you open up is to know a new motoring adventure"(Sales brochure) The adventure continues!

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theoldman
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Joined: Mon Feb 08, 2016 2:39 pm
Location: Bacton on Sea, Norfolk UK

Re: Conquest Drophead overheating

Post by theoldman » Tue Nov 28, 2017 11:14 pm

Agree with Simon - recore the rad with a modern double core.

Neil
Normal for Norfolk

Crossley Stephenson
Posts: 164
Joined: Wed Feb 10, 2016 9:15 pm
Location: Victoria, Australia

Re: Conquest Drophead overheating

Post by Crossley Stephenson » Wed Nov 29, 2017 7:45 am

Hi David,

Have had similar issues on various cars; gone down the cheapest route; in the end it's the radiator! My SP was always running warm, I flushed and flushed and replaced coolant, it was still to warm for me. Had the radiator checked; seriously blocked! A recore and it now takes quite a while to warm up, may need a blanking plate in the winter.

Grasp the nettle and take the rad out and get it fixed.

Good luck
Michael

David Williamson
Posts: 3
Joined: Mon Feb 15, 2016 10:41 am

Re: Conquest Drophead overheating

Post by David Williamson » Wed Nov 29, 2017 9:27 am

Gents,

Many thanks for your thoughts. I haven't had the radiator checked so it may well be blocked.

regards

David

Salmons
Posts: 323
Joined: Thu Feb 11, 2016 7:56 am

Re: Conquest Drophead overheating

Post by Salmons » Wed Nov 29, 2017 9:32 am

I know it would not be original but is it worth fitting an Aluminium radiator?

Dennis

Fossil
Posts: 369
Joined: Sat Feb 13, 2016 5:08 pm
Location: Helensburgh, Argyll

Re: Conquest Drophead overheating

Post by Fossil » Wed Nov 29, 2017 12:06 pm

David

In the unlikely event that replacing the radiator core doesn't help things I suggest that you grasp the other nettle - take out the core plugs and rod out the block thoroughly to remove accumulated rust debris and casting sand residue, which is usually most pronounced around the rear two cylinders. I did this after acquiring my Century in 1994 and it has never overheated in the circumstances that you describe.

I have had to fit a red rotor arm to stop the engine stalling in stationary traffic in hot weather, and I have also fitted a 6 blade fan which may help to keep it cool in the most trying circumstances, but I've no doubt that clearing out the block has been the most effective measure.

Regards

Geoff

New Dexter
Posts: 322
Joined: Fri Feb 12, 2016 9:41 am

Re: Conquest Drophead overheating

Post by New Dexter » Wed Nov 29, 2017 12:25 pm

On the subject of cleaning out items. I had a V8 engine apart some years ago and decided to remove the plugs at the ends of the crankshaft journals only to find an extraordinary amount of solid grey matter inside.
On the radiator front. Someone suggested, again years ago, that it might be an idea to back flush the system. I connected the garden hose to the heater, held my finger over the other end and after a few seconds of pressure build-up removed my finger. Again lots of muck. Presumably it would be possible to do that with a car's cooling system.
Geoff Douglas' idea is good, providing one can do it without too much contortion!

simonp
Posts: 322
Joined: Mon Mar 07, 2016 9:59 am
Location: Birmingham

Re: Conquest Drophead overheating

Post by simonp » Wed Nov 29, 2017 7:29 pm

The Daimler V8 is quite well known for large amounts of silt mostly made up of the orginal casting sand I believe. Some leave the blocks in tanks for several days to release all the muck.

When thoroughly flushed I think they are unlikely to overheat ever again.

SimonP
Daimler SP 250 - "To feel its eager response as you open up is to know a new motoring adventure"(Sales brochure) The adventure continues!

Stan Thomas
Posts: 377
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: Conquest Drophead overheating

Post by Stan Thomas » Thu Nov 30, 2017 9:55 am

If your doing a complete overall it is well worth having the block acid dipped - (a firm in Netherton has quoted me £40 to do mine). Also, have the rad properly serviced or recored, as not only will it most likely be silted, but "new" engines run hotter in the early stages.

'ears a-goo (as they say in Birmingham) where I "did my time" (as oppossed to doing time) if you had a new or factory reconditioned engine fitted, a serviced radiator was automatically part of the job.

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