Bouncing temp gauge

AlWilliams · Post by **AlWilliams** » 06 Jun 2004, 20:23

Hi there,
Hope someone has an idea what this is.
I own a 93 ZX TD with quite a few miles on it, used to run very happily with a steady temp gauge (85 degrees ish) under virtually all driving conditions. Recently whilst trying to get the full throttle black smoke under control for an MOT the local garage had a tinker and have significantly reduced the soot to almost nothing.
They state that the fueling has been adjusted, ergo, they used the maximum fuel setting and the boost compensator.
Now when I drive the engine is up to temp in a much shorter time, and under heavy load conditions the gauge wastes no time in reaching over the 90 degree mark, where the fans cut in. Only do fall back towards 80 under light throttle, fairly quickly.
This cannot be good for the head gasket!
Oh, I also put in a tin on 1/2 tank, of 'diesel cleaner and conditioner' from a company called advanced maintinace chemicals,
I would greatly appreciate any advice on sorting this bouncing gauge problem.
Many thanks
Al.
P.S. I have asked the garage to rectify, but the bloke who knows XUD's (?) is now in Spain for two weeks!

AndersDK · Post by **AndersDK** » 06 Jun 2004, 21:24

Above all - be sure the coolant level is correctly topped up.
Next, try park the car nose up, then let engine reach normal operating temp in idle, to see if any air locks moves up the filler cap.
The most common XUD/hg killer is in-adequate cooling.
I'd say you should extend efforts to really have the cooling system flushed, ensuring it's not restricted, even removing the rad for a real good repeated back/forw flushing.
PS : When I did my last XUD (BX n/a 19) hg, it was clear that the many years of running service had partly clogged the hg thru holes, with calcium & sediments, thus imposing temp imbalance over the cylinder head.
This can no doubt be rectified timely, by running a mix 50/50 vinegar & water in the cooling system now & here in the summertime.

AlWilliams · Post by **AlWilliams** » 06 Jun 2004, 23:30

Thanks for the reply Anders
The coolant system is topped up and bled, nothing has been changed since or before the fueling changes.
I checked as per your recomendation, no air are locks aparent. Is the cooling system likely to be the cause, or should ~I still suspect the fueling?
Many thanks.

AndersDK · Post by **AndersDK** » 06 Jun 2004, 23:48

Diesels do not suffer from heat problems like petrols, caused by wrong fuelling.
Overfuelling a diesel means black soot in exhaust, while underfuelling means weak engine.
As the cooling fans cuts in according to the gauge, you should go on pursuing any problem in the cooling system.
Note the cooling fan(s) should cut-in at stage 1 with lo speed, only occasionally going to stage 2 (hi speed) in slow city traffic.
If hi speed always come in, it's the thermoswitch in the rad that's gone.

Post by **philhoward** » 07 Jun 2004, 01:10

Severe overfuelling can cause the temperature to increase quite dramatically; the opposite to a petrol (where running "lean" causes higher temperatures).

aido · Post by **aido** » 08 Jun 2004, 04:27

what is the normal operating temperature on xuds? mines a zx turbo and once warmed up runs at 80 unless caning it when it will run at 85/90. The citroen manual for the zx says the guage should read half way once warmed up,this is 90 then isnt it? ive fitted a new thermostat and temperature guage sender unit but still same.