I filled the engine coolant up the other day from cold as part of my montly checks, it only took half a cup full.
Ive just been on a 40 mile motorway trip and as its only 4 degrees C out there today the car never got up to its normal "half way" temperature due to the cool air hitting the engine.
Soon as I pulled off the motor way the "Low engine coolant" light came on, as I had slowed down the temp went up to half way but never overheated. I pulled over and check the levels of the coolant and they seemed fine the same level as when I did my refill a couple of days before. I turned the car off went into the shop to buy some water for my journey home just incase. Checked the level again and nearly all the water had gone???????
So I filled it up turn the car on and it started to bubble over at me, I put the cap back on and did another 40miles to get home again.
When home I check again and it had used a little but the light never came back on after topup, checked again 10 mins later after the car had been stood and its taken over half a tank again.

Any ideas whats going off? Faulty senor? Broken Pump? Head gasket?
The car is a 98 with 154k.

Cheers

 

Can you smell/see coolant ?
What's the oil level doing?
Is there 'mayonnaise' inside the oil filler cap ?

 

That temp. gauge is useless in an overheat situation. I think it reads mid -scale until temp reaches 230 F or so, then goes to red zone, but that may be too late. If the coolant level is too low, the temp sensor, located near the thermostat, may not have any coolant to read. Gauge reads mid scale or less, again. If your thermostat is functioning properly, the engine should reach operating temp, regardless of ambient.
If you do not detect the odor of antifreeze under the hood that could indicate a head gasket failure, as the coolant must be going somewhere.

 

Cant see any coolant on the floor, no steam when hot, cant really smell any although the engine always has a slight smell to it when hot.
Oil level is good right in the middle of high and low, serviced 2000k miles/1 year ago.
No mayonnasise inside oil filler cap all clean top of engine.

 

The engine temp gauge only reaches mid temp when going round town this time of year, on the motorway in cool weather it doesnt reach half way and ive noticed the inside heaters dont work as well either and I have to turn them up a bit more till I pull off the motorway then they get hotter again. Its been this case with the heaters and gauge for a couple of years now if I remember correctly.

 

You should have a coolant pressure test performed. This usually can locate a leak.

RJ237 is correct. Your car should have come up to normal temperature well within 40 miles regardless of outside temperature. This is a potentially dangerous situation if your cooolant level is too low to register overheating.

 

Could it be a broken thermostat or senor if the temps aren’t registering correctly?
I’ve booked it into my local Jag man he said if I check the coolant levels while the car is running ill loose the built up system pressure so will give a bad reading, also that there’s an additional expansion tank where the system takes the water which could explain the drops/rises in levels?
What about the heaters not getting as hot as normal....

 

Lots of possibilities....The thermostat is suspect, the water pump could have worn plastic vanes, there could be a blockage, there could be an auxiliary pump (heater or intercooler) problem, and there could be an internal or (hopefully) external leak....or some combination of these.

 

Great fun...NOT
Thanks for you helps anyways, Ill let the Jagman have a look and Friday and report back.

 

The heater hoses that run under manifold can leak without any sign of a drip. Changing them on the SC engine is a bear from what I have read.
You should probably have your Jagman change the thermostat, they don't seem to hold up well, and on the V8 have a habit of failing in the closed position.

 

Ive also noticed a missing on a cylinder when starting up from cold 1 out of 3 starts just for a couple of seconds then it goes away, could this be related to anything?

I have no white smoke but the car has just used another half a coolant tank for a 1 mile trip home.....crazy!!

 

Just had my "kitten" in the shop on Monday for this. I had dreaded the potential head gasket. But mine was only the thermostat. The housing was leaking. Lovely plastic parts again. Hopefully yours won't be too expensive of a fix.

 

What where your symptoms jnetcrutchfield?
...Any how much was the thermostat and labour?

 

The thermostat housing is something of a nuisance due to the rear bolts, but not a big job. Nothing major needs to come off. The aluminum housing is available from places like Welsh Enterprises for around $75 including new thermostat, if I recall correctly.

 

Half a tank in one mile is a major loss. It's hard to get a good reading on the level if you don't always check when cold, but if you are checking when hot and coolant doesn't come gushing out you definitely are losing it somewhere. The system should be under pressure when hot. The cap could even be at fault.

 

It did come gushing out earlier after I topped it up at the garage and it was hot

 

My symptoms...ran fine. Didn't overheat. But every Monday when I would check her fluids, she would need between 4 and 8 ounces of coolant. No drips or puddles anywhere underneath her. No coolant smell when running the heater, so I knew it wasn't the heater core. But when I got her warmed up and then parked, I could smell the coolant evaporating in the air.

Here's what got fixed by my Jag specialist (not a dealer though):

Thermostat Housing Cap ($9.35)
Thermostat Cover ($35.90)
Thermostat Outlet Pipe ($67.23)
T-stat Housing Hose ($6.85)
Thermostat Housing for V8 ($96.50)
Thermostat itself ($64.99)
Water Seal ($4.97)
T-Stat Housing Gasket ($2.80)
3 Hose Clamps ($4.50)
Coolant-Dex-Cool ($24.80)
3 hours of labor ($297.00)

Not all of those parts NEEDED to be replaced, but they were made of plastic as well and I figured we might as well replace them all now since she's open. This way I don't have to do it later.

Hope that helps!

 

A couple of things to check, the overflow tank, it's tricky to see but it's in the same place as the screen wash tank, but on the other side, see if it's full of coolant. You might just be filling that up.

The header tank could have developed a hairline crack that leaks when pressure builds up. The coolant would just gas off the exhaust/heat shields. It's fairly simple to loosen and check for leaks once the car's up to temp (without removing the filler cap!)

The other favourite has been mentioned, the coolant hoses that run in the valley of the engine are a git to replace, the SC needs removing. The coolant runs to the back and over the trans and exhaust. You might find evidence here after a run also...

The 98's had a black impeller waterpump that failed, replaced with a far better white impeller for 99' cars, it's probably had the updated one fitted already.

The nice thing about the T-stat on the R cars is the housing being alloy they don't crack like the 8's. T stat's a coppers to buy and dead easy to replace too.

WhiteXKR's RealGauge upgrade, easy to install and gives the engine's true temperature. It'd help. I don't have to tell you how these engine's can overheat in what seems like a split second I use one and it's a serious mod.

 

Just heard back from the garage, turns out the head gaskets gone after all.

So do I fix it when the cars only worth 3K
Or do I scrap a mint example and start again elsewhere

 

The problem with starting over is that you have a whole list of potential problems that only show up with use.