Coolant Options

Hi my fellow Jag lovers,
I have a 1986 XJ6 and lately I have been noticing that the thermo meter of the coolant went up to 90 in the afternoon (weather is about 70). Although it is still relatively safe but I just opened coolant and did not see any coolant fluid in there. First off the manual only told you how to check but never told you where the fluid should be to be considered full. In my understanding the coolant tank is the brown one and I did not see any liquid in there, nor any indicator saying the fluid should be there. I guess I am just asking how to actually check the coolant level if the coolant tank is the brown one. If I do need to top it off what coolant do I use? From the manual I can’t find the original coolant and the book also says using coolant solution that’s more than 55 percent. However most cars use 50/50 so I wonder if there is any recommendations out there.

Welcome to the forums Keith.
Original coolant would be green in colour, you need to determine what colour is currently in the engine as some do not mix well and can coagulate.
If you are talking about the overflow tank on the inside fender then yes there should be some coolant in there. The cap on the engine should be showing full. 50/50 is about the most you want to go, I believe any higher does not provide any benefits

The brown tank is the header tank and yes, there should be coolant in there. This is where you fill and/or top-off the cooling system.

Hidden from view, in front of the front tire, in an overflow or atmospheric tank.

I’d top-off the header tank until nearly full and drive the car. Recheck level when cool over the next few days. If the level has dropped a bit, but does not continue dropping, that’s fine. The level will stabilize, probably at about 75% full.


The later cars, the ones with the brown coolant tank, did not have the coolant cap on the engine!


Well thats a bugger :frowning:

Big pipe into the radiator though.
There’s a feature inside the tank, the upper step will be visible and the lower covered. The engine is fine, unless you keep driving like this. The line to the atmospheric catch tank in the wheel well often rusts shut. At any rate, sole coolant may be forced out somewhere until the level equalizes. Remove the rubber hose next to the filler neck and park outside after the first drive. Excess might be forced out there. Also possible that you need to refill once after running the engine as trapped air is forced out. Same color as what’s in there, should be green, will be rusty.

Hi Doug,
I have attached the photo of the engine cover of my car

From what I checked the brown tank did not have any fluid but the one on the right did have a great amount of fluid inside. I assume the brown tank is the expansion tank and the right plastic tank is the actual reservoir. In this case do I need to top it off?

The inside of the front cover look like this. The brown tank I did not see the coolant and I am not sure if it has to be full, on the right the plastic tank did have a great amount of fluid inside, and it says “fill to the base of the neck” so I am not sure if this is the actual coolant tank. The manual says to fill the coolant to the base of the neck but the brown tank didn’t have any indicator. I am just confused right now and not knowing what to do. I drive a few miles today and the meter did not go over 90.
Also the manual handbook says to add coolant that’s no less than 55 percent and I do realize that 5050 is the most common coolant. That’s why I’m hesitant to go to places like jiffy lube to top it off.

50/50 will be fine, buy the concentrated fluid as the premix means you are buying 50% water, thats normally cheaper out of a tap/faucet.
If you are talking about the reservoir that is next to the brown tank that is the washer bottle.
To start I would just use water to fill the brown tank, this will mix with what ever is in the engine block and eventually you should see what colour coolant is in there (if any)

The brown tank is where the coolant goes. Fill it as previously described.

On either side of the brown tank are two white containers. The one towards the front is for the windshield washer fluid. The one closer to the firewall/driver is the reservoir for brake fluid.

The other coolant tank (overflow/atmospheric) is hidden from view, on the underside of the fender, in front of the front tire.


50/50 is fine; don’t worry about 55%


1 Like

What you do not(!) do, Kheitoris is to fill anything anywhere until you know what liquid goes where…:slight_smile:

The brown tank is the expansion tank; as the coolant heats up it expands into the expansion tank - which is also where you add coolant.

At ‘first fill’ (or in doubt) you add coolant to the brim of the brown expansion tank and fit the pressure cap. As the engine warms up the expanding coolant is forced out via the pressure cap through the vent hose at the side of the filler neck - either into an atmospheric recovery tank (if fitted), or simply dumped on the ground.

When fully hot; about 1 to 2 pints has been ejected from the expansion tank - and the pressure in the system is at some 15 psi, the opening pressure of the cap. As the engine cools down, the coolant contracts, leaving the coolant in the expansion tank at a certain level. There should be be a ‘sloping’ ridge in the tank to better assess the level - usually at the notch, as David says.

That your expansion tank is empty is ‘wrong’, and likely means you have a leak - and low levels is likely the cause of ‘warm’ running. So after filling the expansion tank drive the car to heat up the coolant - a couple of heat cycles is likely required to stabilize the level, and expel air, as Doug says. Then check levels with the engine cold(!) - all level tests should be done with a cold engine, for consistent readings. Check levels daily for some time; do not add coolant during testing until a leak is verified and refill is necessary. Find the leak and remedy…

As asides; don’t use less than 30% glycol (for effective corrosion protection) - nor higher than 50%, further increase will not improve the antifreeze effect of the mix. In principle; fill ready mixed coolant to ensure that the mixture remains constant. At 15 psi the boiling point of coolant is 120C, at atmospheric pressure it boils at 100C - and exceeding the boiling point will cause loss of of coolant, adding to cooling problems…

And welcome on board…

xj6 85 Sov Europe (UK/NZ)


Thank you. Since I don’t really know what coolant the last owner added into the car I might just flush the radiator and clean up the tank. Then I’ll add 50/50 in the tank. Is there any coolant that I should add or any 50/50 would just do the trick? I was heard from the last owner that he used a more expensive type of coolant but I am not sure which one he actually used.

Like any type of 50/50?
Since I don’t know what goes in there first I would flush the radiator and clean up the tank. With that I would be able to see what coolant goes in there then I would put the right coolant in there. But I don’t have a huge place so I might as well do it in Jiffy Lube and I don’t know if their coolant is good or not. Do I need to bring my own coolant? If so which one would you recommend?

If you can flush it you should include the engine block and heater matrix. There are types of coolant that gel up when mixed but if you match the type (colour) that comes out that is alright.

Put something green in, ~ 50/50 or premixed.
Replace the coolant every 2…3 years.

Any antifreeze suitable for aluminium will do, Keith. There are some fancy stuff out there, which may recommend different mixtures, but good oldfashioned ‘green’ glycol is the default option…

However, before you change the coolant - fill up the expansion tank to the brim, with water or mixture, and replace the cap. Then drive the car through heat cycles, and check level with the engine cold - just to verify if you are indeed loosing coolant. There is no point in replacing the coolant before you have checked for leaks - and remedied…

When filling the system from empty; fill half the amount of mixture into the expansion tank - ensure the AC is in full heat. Then start the engine and let it idle while continuing filling until the expansion tank is full - then replace the filler lid cap. Drive the car a couple of times, let the engine cool off and verify level to the ‘notch’ - adjusting if required…

xj6 85 Sov Europe (UK/NZ)

And don’t worry, some water will be forced out as the car cools down and the heat from the block is no longer transported away by the water pump, that’s why you want to park outside just in case.

I went to Jiffy Lube today and they put on Extended life in there. I am not scared that this may damage my car. Do you think I should flush it asap or this is actually fine? From the guy there he said Extended life mixes with others fine and I don’t need to stress too much about it. But as I do more research it said extended life is more for trucks not cars…

I went to Jiffy Lube today and they put on Extended life in there. I am not scared that this may damage my car. Do you think I should flush it asap or this is actually fine? From the guy there he said Extended life mixes with others fine and I don’t need to stress too much about it. But as I do more research it said extended life is more for trucks not cars…

If he says it mixes don’t overthink it, trucks and cars are the same thing, we even get the same mpg.

Coolant is basically ethylene (and sometimes propylene) glycol with some additives. There’s two things to watch out for, silicates and then there’s a newer stuff but that won’t find its way into old cars normally.