Overheating

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mark1968
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Overheating

Postby mark1968 » Tue Jun 29, 2010 5:43 pm

I have a 1986 3.6 manual, and when i use my air con, the temp gauge moves from being just below the N (normal) to 3/4 high. Is this normal? Also, when i have AC on, the engine always stalls at a junction as i dip the clutch. Normal tickover is about 800 rev, but the AC brings it down so low the engine stalls. I've raised normal tickover to about 900, and this helps, but now if the AC is OFF, the engine sounds like its running at fast idle. All filters and plugs and rotor arm and dizzy cap have been replaced, but it hasn't made any difference.
Any ideas please?
Mark

almcl
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Overheating

Postby almcl » Tue Jun 29, 2010 7:28 pm

Switching on the air con does place an additional thermal load on the system so a slight rise in temp isn't unusual. Is the temperature really rising (check with an IR or other type of thermometer) or is it just the gauge reading?

There's a supplementary air valve fitted to later cars (not sure about an '86 but it's present on both my '84 Daimlers) which is supposed to compensate for the extra drag of the air con compressor. It's fitted in a grommet on the forward part of the air filter. It's an electrically operated solenoid valve, so with 12 volts applied it should open. Does yours?
Last edited by almcl on Sat Aug 21, 2010 8:18 am, edited 1 time in total.
Al McL
'93 XJS 4.0 - '05 X type Est 2.0D - '13 XF 2.2D Sportbrake

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dhdove
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Overheating

Postby dhdove » Wed Jun 30, 2010 12:34 pm

Mark

Check this link to my recent thread in the cooling section

http://www.jec-xjs-forum.org.uk/xjsbb2/ ... php?t=1826

When you use the air-con the heat extracted from the cabin is released to atmosphere from the a/c condenser directly in front of the engine cooling radiator, thus heating your engine coolant. If your rad is suspect the eng. temp will rise as it is unable to cope with this heating effect.
The question is how bad does it need to be before you take action - see comments re gauge markings.
Also bear in mind that we are enjoying particularly high ambient temperatures at the moment which has a big effect on cooling efficiency and will amplify any effect.

Regards
Tony
XJS Bulletin Board Moderator
2013 Mercedes Benz SLK55 AMG, 420bhp. Plenty for me, thank you.

Brakebuster
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Overheating

Postby Brakebuster » Wed Jun 30, 2010 5:16 pm

there is also the supplementary electric cooling fan mounted behind the radiator , in addition to the viscous fitting fan ,

this is activated when the air-con is on , as the heat load increases, the electric fan helps dissipate the extra heat


i have read however, that later in production , the link with the aircon was removed, and it just activated when required at any time

BB
1989 5.3ltr V12 XJS Coupé FULLY RESTORED
2004 2.1V6 X-Type Saloon in platinum silver for the good wife
1994 3.2S XJ40 in Morocco Red with Doeskin interior

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dhdove
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Overheating

Postby dhdove » Wed Jun 30, 2010 6:14 pm

BB

Thanks for that forgot to mention to check that the aux. fan is working..........this blows the hot air through your rad..... :roll:

Tony
XJS Bulletin Board Moderator
2013 Mercedes Benz SLK55 AMG, 420bhp. Plenty for me, thank you.

mark1968
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Overheating

Postby mark1968 » Wed Jun 30, 2010 10:48 pm

Many thanks for replies. I've now got another rad to fit. The old one blew and when i removed it, it had fins badly damaged, blocked and quite a few were actually missing. It was difficult to spot all of the problems while it was in the car. I was quite shocked when i saw how bad it was. Does anybody know if old rads are used by any companies, or should i just get £5 for it from my local scrap yard?

Regards, Mark

almcl
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Overheating

Postby almcl » Thu Jul 01, 2010 10:05 pm

Old rads can be recored by your local radiator shop. This replaces all the cooling tubes and fins. It costs about 1/4 or 1/3 of a new radiator.

One specialist keeps a stock of old radiators for the cars he works on and when a car needs a replacement he sends one of this 'stock' off to be recored while he removes the old one. The result is usually a same day turn round on a radiator replacement.
Al McL
'93 XJS 4.0 - '05 X type Est 2.0D - '13 XF 2.2D Sportbrake

mark1968
Posts: 13
Joined: Sun Oct 18, 2009 8:52 pm

Overheating

Postby mark1968 » Thu Jul 29, 2010 7:17 pm

Thanks for info about extra air valve. Mine is definitely not working. There is 12V there as AC kicks in, but valve is dead, as i tried a direct supply to it and nothing happened. Does anybody know the part number? I can't find it in my catalogue or on websites from manners, robey or barrats.

1986, 3.6 manual vin 135303

Cheers, Mark


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