Hi Warrjon

I agree with you and Greg

But knowing how overheating can destroy an Engine, I was maybe understandably a little bit Paranoid.

Unless the Photo of my Gauge, is starting to Freak you both out, by showing too Cold.

 

My gauge runs higher than that. Each temperature sender has a tolerance in its resistance so the gauge will read differently with different senders.

One thing I have noticed is the gauge moving as the voltage varies. All of the gauges work based on voltage divider as the resistance of the sender varies the gauge will respond accordingly. If the supply voltage varies this will effect the reading on the gauge.

The XJS does not use a regulated voltage supply to the gauge pod so gauges will vary with voltage.

 

Cheers Warrjon

That is very handy to know.

 

OB,

I think it's perfectly feasible that you might have a sender unit whose resistance readings are causing that gauge to read low. However, it might also indicate a cold-running engine consistent with a permanently open thermostat.

I would be tempted to start taking some temp readings, but perhaps easier, check that the 'stat opens only when it reaches temp. You should be able to suddenly feel (and possibly hear) the warm coolant start to flow on the rad side as the 'stat opens. If the temp just gradually rises on that side (and doesn't get really hot) it could indicate that the 'stat is stuck open.

Paul

 

My oil pressure gage is barely above 0 when at idle and goes up to 50 at highway speed.

 

My gauge doesn't really go to 1/2 anymore, so I either run really cool or it's busted, which has happened to my voltage gauge, but there is also no reason to suspect a problem.

So every once in a while I check the temp by pointing an IR thermometer at the radiator hoses and other general areas.

After you drive it for 6 months and then check and it is actually fine, you learn to trust it.

 

Hi Paul

This is one time that I hope you are wrong but you could be right.

So I will take some readings and report back to all, to see what you think.

 

Hi Mac

Same here (sort of) what you are seeing on my Oil Gauge, stays pretty much at that level (Magnetec 10/40 Semi Synthetic) until Highway Speeds, when like yours it goes up to around 50.

 

Hi Sidescrollin

Great idea, once again!

I've got an IR Thermometer, so I'm going to take some readings and then we can compare notes and see what we get.

 

when i picked up my xjs i took it to a friend who has a lift to check it over.On the way back i stopped at a junction and to my horror the oil pressure had fallen on the floor on tickover. After changing my underwear i ran the car and everything looked and sounded ok.
i later found a problem with a crap battery. After changing said article, the oil pressure guage read fine on tickover and all speeds. perhaps a check on the battery condition and the charging voltage may be in order

 

I'm running 20/50 --100% synthetic.

 

Hi Leo

Thanks

But its not the Battery, I just splashed out over £70 Quid on a Brand New Exide.

 

Hi Mac

Someone else will probably know but I suppose that could make a difference.

 

This is quite normal for the XJS oil pressure gauge.

The thinner the oil ie 10/40 will cause lower oil pressure due to the thinner oil. Think of it like a garden hose. Turn the tap on (with no nozzle on the hose) and water will flow out and travel about a foot (low pressure) put your finger over the end and water will squirt much further, the same volume of water will flow.

As long as the volume of oil is enough to lubricate the engine low pressure is not so much of an issue. The 6.0L will run higher pressure as the bearing tolerances are much tighter than the 5.3.

 

Hi Warrjon

Many Thanks, I won't be so paranoid now.

 

Here is a pic of my temp gauge after I replaced the sender with a brand new one. Disregard the oil pressure as I broke the spade terminal off and had not fixed it at this point.

The coolant temp with the gauge at this point was 90°C

 

There is one factor I haven't seen mentioned. The V12 has TWO thermostats, one for each bank, but only one temp sensor. It is possible that the stat on the bank w/o a sensor could stick closed and not have it show on the gauge

 

For a bit, yes. The B bank thermostat could stick shut. If it did, the B bank water circulation would go into the crosspipe and down the short pipe to the water pump housing where it would mingle with the cool water coming in from the radiator having entered the rad from the A bank thermostat.


Some of this mix of uncooled and cooled water would recirculate through B bank, but some would go into A bank and start to show increased water temps before too long, at least in hot weather anyway. Then the alert owner would stop and investigate and find the B bank top hose was cool, and know the stat was the problem.


Knowing your gauge's position when all is well is, as several people have said on this thread, very important. When I did a bit of a gasket overhaul on my engine, I also did the "Lutz Mod". This is a modification to the front water manifolds' orifice sizes so that water is forced towards the rear of the engine. This is to stop any tendency for the cooled water to "short circuit" the engine by exiting the water pump, then entering the head, then returning straight into the front water manifold rather than flowing all the way to the rear of the engine. In racing V12s, this mod is considered essential, though whether it is needed in a road car is far more debateable. Anyway, I have done this mod, and it certainly works. Immediately I did it, the gauge temperature reading went up to a "new normal" position by two or three needle widths. The explanation for this is that indeed water is circulating better, so the temp sender is seeing better flow from the rear of the engine, and less "short circuit" flow of cooler water, so that is why the temperature is reading higher on the gauge because it is seeing a better mix of coolant. The cooling is actually better, in the sense of being more even throughout the engine's length, but the gauge is reading higher even so, because it is seeing a more representative mix of coolant!
Greg

 

To beat the same horse I've beaten many times before, coolant *flow* it what should be paramount in everyone's mind. Coolant temperature is secondary....to a certain degree (ha ha)

Cheers
DD

 

coolant flow is important, but would the restriction actually reduce over all pump flow?

true that the available flow would be forced to the rear, and help cooling V12!

its about time someone actually made a coolant pump that produces higher volume and higher pressures!

i have modded pumps on other type engines , and they worked quite excellent!

(darn i miss my machine shop).