Radiator over flow tank gets filled up itself!

[Aben Dean]

i just noticed that since yersterday the Radiator overflow tank gets filled up with water from the Radiator..... what can cause this?? The water in Radiator gets bit less (because it comes into the the reserve tank). it doesnt get hot nor boils..... any ideas what it can be??

[Robo]

You could try replacing the rad cap.
A cause can be, the vacume function in the cap fails.
Faulty cap doesn't allow fluid to be drawn back to rad while system is cooling down, some air may even enter instead.

[Cuppa]

We had a similar situation in our Civilian bus when travelling up WA's west coast. The overflow bottle would fill, but the coolant didn't get sucked back into the radiator when it cooled. The motor (3.3l 4 cyl diesel) continued to run fine, no evidence of overheating or any other problem. Having put on a new radiator cap & renewed the hose between radiator & overflow bottle (the latter in case of a pin hole air leak) & being on the northern half of WA's west coast where services weren't available we pushed on toward Darwin, siphoning the overflowed coolant back into the radiator at the end of each day's driving once the motor had cooled.
Things gradually got worse & worse, with siphoning needed more frequently until eventually at 60kms short of Katherine we had to stop as siphoning was getting us just 20kms before the coolant bottle overflowed. At all times the motor ran perfectly except for this problem. In Katherine we had to get the complete motor replaced because the cause was a blown head gasket (blowing between cylinders) which had resulted in erosion of the cylinder block to depth of several milimetres making a replacement motor a cheaper option.

I should add that we had had the cylinder head gasket replaced - twice - in Geraldton & I consider that they failed to do what was needed at the time (machining the top of the block when it would have made a difference). We had also checked for evidence of oil in coolant & coolant in oil, & found none in either.

So. based on our experience ..... if a new radiator cap and/or radiator to overflow bottle hose don't fix the problem, I'd suggest that it would be wise to get the cylinder head off & see what's going on sooner rather than later.

Cuppa

[Aben Dean]

oops..that sounds scary! we had a complete rebuild of the motor few months ago and the head was tested that time and new head gasket was fitted as well. no coolant in oil...no oil in coolant i checked.......have a task on hand now to find out what it is. water pump has anything to do with it??

[Cuppa]

Others may know better than me, but I can't see how it could be related to the water pump. It is normal for coolant to be pumped into the overflow bottle as it gets hot & expands. What is abnormal is that it isn't being sucked back into the radiator when the motor cools. As far as my understanding goes this can only be caused by two things, either an air leak meaning that when the coolant in the radiator cools air gets sucked into the radiator rather than the coolant from the bottle (radiator cap or hose between radiator & bottle), or that the radiator is remaining pressurised. Fingers crossed that yours is the former.
I hope someone else more knowledgeable than me might chip in here, as I am far from an expert, just relating my experience.

Cuppa

[georges80]

Head gasket failure is a possibility or even a cracked head that 'pressurizes' the coolant system. In the US you can buy kits to test for exhaust contamination in the coolant, can you get them in oz?

cheers,
george.

[MQ MAD]

Throw a new radiator cap on it and check it regularly
Fill radiator to top, fill over flow bottle to full mark
Then watch and see what happens
Cost ,what about $10,$15, then come back with what you find
From there could be a blocked radiator,causing excessive heat and over flow bottle can be heard bubbling water
Take the plugs out and check for maybe 1 or 2 with discolouration compared to others,or wet /rusty plugs, that could be head gasket issue
Also check dipstick for water molecules on it or milky oil,but those 2 are extreme,just go with the new cap and watch it

Just remember ALLOY head hate too much heat,wether recoed,or not heat up an alloy head and itll crack .......

[gf0012-aust]

had this problem a couple of years back - turned out to be a cracked head.
rad pressure test was normal
rad cap test was normal
exhaust gas test was normal

PITA

[Aben Dean]

Hopefully mine gets solved without replacing the head!..... Radiator is all good. will see how it goes.