Morning and happy Monday,

Mind if I bounce this one off you? Every 2 months or so I top off the coolant level with a tiny amount. Maybe it's down 1/2 to 3/4 inch in the resivour

This weekend I went on a 750 mile round trip visit. On the way home, 10 miles from home, my low coolant light started cycling. Nose down, light up. Up hill light off, >1 minute level, light off.

Well with my RealGuage I wasn't worried. Engine temp rock steady. Checked her when I got home and settled. Sure enough I had to add coolant. Warning light is functioning properly.

So I figured I have a slow leak somewhere. A cup, or whatever it takes to trip the warning light, every 700 miles or so. . . Time to pressure check.

Sidebar: don't forget to wet/moisten the rubber washers that contact the connections on the pressure checker and connectors. I spent 20 minutes trying to figure out if the pressure tester I hadn't used in 18 months was bad as I listened to air escaping with each pump.

Applied pressure - nothing! She's holding 18 pounds for >20minutes. The lower radiator hose was pressured, therefore radiator is being tested right? Had an oil change before the trip. Oil still clean, clear, proper color. Not the head gasket right?

Any thoughts or suggestions on where or how to track this down?

As I type, I just realized that I probably drive 700 miles in 6 weeks or so. She sure doesn't lose that much fluid during daily driving.

Upper radiator hose does not collapse, which would be a sign of bad radiator cap.

Thanks, John

 

I had asked what the oil looked like, then re-read the post. I'm an idiot.

 

air in system?? Possible pin hole leak in tank which may not show until at operating temps (I do have an extra brand new one if that).

I would think any connections that may be weeping would show under pressure

 

Well, there is water going to and from the heater core, through the valve and electrical pump. Hard to reach, but some can be checked visually. Core would be by smell, or by inspecting the A/C drain holes.

There are the valley hoses, where leaks might not be readily visible. Could pool on top of the engine for a bit.

There is also water around the EGR valve if you have one. Not sure if cycling the water has anything to do with the EGR valve being open.

There is of course the transmission oil cooler in the cold side of the radiator end tank, so it is possible the coolant can leak into the transmission. Never head of it on our cars, though.

Last, there is the whole recovery tank mess behind the wheel well liner. Maybe coolant can be pushed to it, but somehow not sucked back in. Maybe an old plastic line is cracked, or you need a new cap.

Best of luck, keep us posted.

 

The recovery tank idea is an interesting thought. Issues there might not show up under a pressure test.

The car will dump excess coolant via that recovery tank if overfilled. Is it possible the car is misreading the coolant level as...too high? And then dumping too much coolant as a result? I am pretty sure this is done mechanically rather than at the bequest of a sensor, so I imagine this is unlikely. Right? Someone correct me on this.

 

How old is your coolant expansion reservoir cap? When the cap is faulty, it allows coolant to move from the coolant expansion tank to the larger recovery tank in the wheel well but does not allow coolant to return to the coolant expansion tank from the larger recovery tank in the wheel well. My wife's 2006 XK8 has done this a couple of times during our ownership. A new cap solved the issue both times....

 

So, may or may not apply to your car, but just fixed an incredibly slow leak in the upper radiator bleed line. Coolant reservoir went from full to indicator light in a month or more. Was blowing by the bit of hose on the flexible hose connection (~10 cm) near the radiator. Produced some fluid marking on the outside of the lower radiator hose very near the radiator below the bleed line. It would not surprise me if that leak or similar leaks held pressure.

Replaced that bit of flexible hose with some silicone heater hose and is pristine now.

 

Dale
Steve
Fmertz
Jon
Enjoy every sandwich,

Thanks to each of you. Looks like I've got some leak hunting to do.

The radiator cap is around 2yrs old.

I'll post the solution when I find it.

Thanks again,

John

 

Hi John,

One more thought to add to the good suggestions you've received so far: the water pump seal can tend to leak more while the pump is operating. Because of its location it can be difficult to see a small leak from the weep hole, and leaking coolant tends to be blown away by the cooling fan. You may be able to see coolant residue below the pump with a strong flashlight and mirror, or an inspection scope if you have or can borrow one.

Cheers,

Don

 

Don, great point, thanks!

John

 

I've had a similar problem leaking small amounts of coolant over weeks or months. It turned out to be more than one leak

I found in the end.

1) the water pump was leaking because there was staining on the gasket, and in addition there was a plastic button rattling around the impeller. How that got in there I don't know, but it seems to be from the pellum connector, but that wasn't the whole solution.

2) the plastic connector at the back of the engine which joins from the metal valley pipe to the heating hoses was cracked underneath, the water leaking and dripping onto the hot exhaust pipe, and so evaporating.

3) the water header tank had a loose connector.

When I fixed all three problems, the low level warnings never appeared again.

 

I have a slow leak in my octopus hose right behind the throttle body, slow enough that within minutes after turning off the engine the coolant has evaporated. It made it pretty hard to spot.

The leak mainly seems to happen when I have the heater on. I haven't yet broken out a schematic to figure out why that might be.

Point is, different operating conditions of the car--motors, valves, etc--can impact leaks, maybe interfering with your pressure testing.

 

Slow leak RESOLVED

Don gets the prize for this solution.

Recently another member told his story about the overflow tank cap being the culprit.

It's been a slow, but constant leak for a few months, I tried it. Bought a new cap for about $12, gave her a spin.

Stopped at a store, shopped, and started to back out of the spot. BAD NEWS, now there was visible spot of leakage starting to form a puddle.

Well I had 8 miles to get home, drove it carefully, eye on temp, waiting for low coolant warning. Just as I pulled into my driveway, got the message.

Figured, ok now the leak is worse, should be easy to find. (Yeah right...)

Opened the hood and took a look - there were spots of coolant everywhere.

Took a bit of rinsing with the hose, then a bit of idling (in addition to the fans, the moving belt, it looks like 50mph air flow sure adds to the scattering)

Finally, I could see drip drip from around center left when viewing head on.

I actually had to use a small mirror on a telescoping handle, engine running to find it - there was a small steady stream from the bottom of the water pump (5yrs old) into a vertical crevice which led down to bottom of engine.

Don, I think you were 1st to suggest the pump, you were right, thanks.

I found the price of these pumps more than doubled in the last 5 yrs.

Another one for johnken's dont do what I did lessons learned file:

Take the time to visually ensure the belt is centered on the bottom pulleys before you start the engine. If they move off between the pulley and the engine block, tension will seem right. Problem is: running the engine for just a few seconds like that ruins the belt. Mine lasted, oh about 1 block after that. (Ouch)

The funny part is it actually took longer to install the new belt than to replace the pump. The bloody thing is like a rubics cube with a mind of its own.

I should have just pulled out the fans, did not save time by skipping that. Hell of a coincidence that this changed exactly when I switched caps.

Thanks to everyone for your help and suggestions. This is resolved.

John

 

Congratulations John! Glad you figured it out!

Note that the water pump Jaguar now supplies as a replacement is the Airtex AW4124, which has the correct plastic impeller to tolerate the OAT coolant. The Jaguar price is around $375.00, but Rock Auto's price is still under $35.00.

I'm marking your thread RESOLVED!

Cheers,

Don

 

Just to make sure, you're sure coolant wasn't/isn't leaking from around the new cap? You might have added a second leak with the cap.

This happened to me. Trying to track down my leak I bought a new cap from Rock Auto, but the new one didn't really seal at all. It went on REALLY easy, but it turns out that's because the O-ring wasn't engaging. I went back to the old cap.

 

Volkris, thanks I will check. Still have the old cap so at least I'm covered there.

John