Coolant Mystery

[Mels Truck]

Any suggestions most welcome...
During a long drive temp started going up, was a hot day and I was doing 70, dropped to 60 and temp went back to normal. Checked levels this morning and expansion tank is very full, way over max level but radiator appears to be empty. Any ideas where to start solving the mystery .....

 

[clivehorridge]

Assuming no obvious leaks, I would start with something simple, like renewal of the rad cap, if it hasn't been replaced recently.

A cap that doesn't hold sufficient pressure will release coolant to the expansion tank prematurely, thus starving the cooling system of coolant necessary to maintain normal running temp, at those external temps.

 

[Mels Truck]

Assuming no obvious leaks, I would start with something simple, like renewal of the rad cap, if it hasn't been replaced recently.

A cap that doesn't hold sufficient pressure will release coolant to the expansion tank prematurely, thus starving the cooling system of coolant necessary to maintain normal running temp, at those external temps.

Hi, thanks for reply. Radiator cap was replaced recently, also new cylinder head a few weeks back. Just been out having another look, large wet patch below expansion tank. Assume not expansion tank as that's too full, thinking radiator but why has expansion tank not drained into empty radiator?

 

[Ben Stratford]

Is the pipe within the expansion tank still attached? If not the coolant may not draw back properly

 

[Mels Truck]

Is the pipe within the expansion tank still attached? If not the coolant may not draw back properly

Yes it appears to be. When I got home after the drive I checked the expansion tank, way over max line. Overnight it's dropped a little but still way over max line (couple of inches from the top). Radiator was low, just topped that up. Will see if it stays full. Radiator is not in the best condition. Any suggestions what to check most appreciated.

 

[clivehorridge]

If you've been to the trouble and expense of sorting out a new head gasket, I would go the extra mile and replace the radiator, a likely cause of of the head gasket failure in the first place.

Whilst at it, a new thermostat wouldn't go amiss.

 

[Mels Truck]

If you've been to the trouble and expense of sorting out a new head gasket, I would go the extra mile and replace the radiator, a likely cause of of the head gasket failure in the first place.

Whilst at it, a new thermostat wouldn't go amiss.

Thank you, radiator was next on the shopping list as something that needs replacing. I'll add thermostat to the list too. I did wonder whether having replaced the cracked head it would show up other weak/failing components now she has a new lease of life!

 

[clivehorridge]

Thank you, radiator was next on the shopping list as something that needs replacing. I'll add thermostat to the list too. I did wonder whether having replaced the cracked head it would show up other weak/failing components now she has a new lease of life!

I know funds are often the culprit, but most head gaskets go because of overheating, and if you have some blocked cores, then this could have caused the failure, particularly in rather extreme conditions, such as high ambient temperatures.

Summer here can be close to or above 40C for weeks on end, so cooling systems have to be in tip top condition. I've had a rad burst on my 80, and replaced it with a genuine OEM, €500 euros, but I don't regret it. That was about 8 years ago, and I've had no cooling issues at all, since.

Highly recommended...

 

[TL75]

Best thing to do before anything else is just get your radiator serviced and buy a new radiator cap with he correct PSI rating for your radiator.

 

[BobMurphy]

thinking radiator but why has expansion tank not drained into empty radiator?

There is a two-way valve in the Radiator Cap. As the Radiator cools a partial vacuum is formed that allows Atmospheric Pressure to push fluid from the Expansion Tank back into the Radiator via the Radiator Cap.

If the Radiator Cap is faulty, or, if there is a leak in the Radiator or its pipework you won't get a vacuum so no fluid going back into the Radiator.

I hate to say it, but it sounds as though your new cylinder head gasket is leaking.

I had the same thing, fitted a new head, gasket, bolts etc. but within a week or two it was leaking. I took it apart and this time put a thin layer of gasket cement on both sides of another new head gasket and torqued it up with another new set of head bolts - no trouble since.

Bob.

 

[clivehorridge]

There is a two-way valve in the Radiator Cap. As the Radiator cools a partial vacuum is formed that allows Atmospheric Pressure to push fluid from the Expansion Tank back into the Radiator via the Radiator Cap.

If the Radiator Cap is faulty, or, if there is a leak in the Radiator or its pipework you won't get a vacuum so no fluid going back into the Radiator.

I hate to say it, but it sounds as though your new cylinder head gasket is leaking.

I had the same thing, fitted a new head, gasket, bolts etc. but within a week or two it was leaking. I took it apart and this time put a thin layer of gasket cement on both sides of another new head gasket and torqued it up with another new set of head bolts - no trouble since.

Bob.

While you very well be right Bob, so far Mel has only said he's experienced a slight rise in temp which reduced when he slowed down.

Coolant has migrated to the expansion bottle, meaning the system has pressurized more than his cap pressure and the level is higher than the mark on the expansion bottle, suggesting he didn't have an all out boil or high pressure from the cylinders (leaking head gasket).

He's also said the coolant hasn't been drawn back into the system.

It's only supposition, but this sounds like a classic cap problem, where the release pressure is too low and it's not sealing properly to create the 'vacuum' as it cools.

He should get the rad checked, the cap seating may be damaged or the cap may be faulty. The rad under operation could be a real mess for all we know, but you can change the head gasket 20 times and still have the same problem if the rad is not cooling efficiently.

 

[BobMurphy]

Yes, I agree that the radiator is the best place to start (and the easiest). When mine went I had already fitted a new rad (well, actually two as the first one I received from Milners had a hole stabbed through it - but not through the box it came in !).

No doubt the cause will become apparent as this thread unfolds.

Bob.

 

[Jack VZJ90]

Hi Mel,
I don't know if you fixed the problem yet, but i had the same problem a few years ago.
Normally they change coulant every two years ? By the look in your overflow tank you can tell the condition of your fluid. Should be red - rose ! (for aluminium engine's suitable) If it's dirty and dark by now, most likely your radiator is clogged. (appears around 200.000 - 250.000 km) When you drive it, you don't recognize anything, but when the engine really has to start working temperature rises quickly. Too long driving in this condition will give you a cracked head, or blown gasket.
Now comes the tricky part. If gasked and / or head is replaced, and you have a new radiator installed with new filler cap with the right PSI valve !!! the inside of your engine is cleaned by the new coulant. This dirt / sludge will go to the top of your radiator and when coolant expands go through the valve in your filler-cap en end up in the overflow tank. When coolant cools down, it's sucked back into the radiator. One problem ! the valve in your filler-cap get's blocked. this can be a repeating process. I had to clean this filler cap at least 5 times before all the dirt was out of the system. The best way to clean the inner of your overflow tank is to slide the tank out, and put some water and small gravel and in it and shake it completely clean.
I learned my lesson out of this problem, and drain and renew my coolant every 2 years.
I also renew my brake fluid every 2 years, since i installed new front and back brake calipers.
Good luck,
Jack