The Mitsubishi Pajero Owners Club®

chris parry · Posted: Sun Sep 30, 2018 11:35 Post subject: radiator expansion tank full

Shogun Equip 3.2DiD long wheelbase 2004
Long journey on motorway yesterday. First 100 miles no problem then suddenly temp. rose to maximum and heater started blowing cold.
Reduced speed to 50mph and temp fluctuated between Max and Normal depending on going up hill or not.
Pulled into services, engine not overheated but radiator expansion tank full to the brim. Got home slowly.
Next day with the engine cold, expansion tank still full. Any ideas would be much appreciated please.

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peteinchad · Posted: Sun Sep 30, 2018 11:51 Post subject:

Cheapest thing to try first is to replace the radiator cap.

NDZ · Posted: Sun Sep 30, 2018 12:26 Post subject:

Dodgy cap would be a good outcome but you have a delicate situation here. If the cap is OK then my guess is you've lost coolant somewhere else and the remaining coolant has boiled over and dumped into the expansion tank. Driving with heater cold and fluctuating temp means there's hardly enough coolant left in the system to work properly with the only get-you-home fix being to let the engine cool down until its safe to open the rad cap then top up the coolant using the radiator as a guide because the expansion tank may no longer be accurate.

The cause of the coolant loss will be the answer and it could be anything from a dodgy cap or a slow leak to head gasket failure and TBH I'd start investigating the worst case first which is head gasket and head failure having driven it hot. With a cold engine, top up the radiator to full and empty the expansion back to normal, start her up with the radiator cap off and watch for bubbles as she warms up for about ten minutes. Youtube is full of vids on this head gasket test and right now I wouldn't drive more than a couple of miles until you sort it out.

chris parry · Posted: Sun Sep 30, 2018 12:49 Post subject:

Thank you for the replies. It's much appreciated.

trekker · Posted: Sun Sep 30, 2018 17:03 Post subject:

After filling the radiator and correcting the expansion tank level as above, look carefully around the radiator and all hoses, large and small.

I'm thinking you have a coolant leak, have boiled the engine, and this rather violent expansion of coolant had filled the expansion tank. Look for evidence of a leak and for the actual leak as the engine heats up.

chris parry · Posted: Thu Oct 04, 2018 20:07 Post subject:

Thanks for your help gents.

On close inspection I found two splits in one of the rubber gaskets on the radiator cap.
Emptied the expansion tank and filled to the correct level, filled the radiator and started the engine and watched for bubbles.
No bubbles found, replaced the radiator cap and when for a long run, about 50 miles. Everything perfect.

Following morning I removed the radiator cap and checked coolant level in the radiator. It required 1/2 litre to fill it back to the very top again. Repeated this for three days after a long journey each day.

My question is this : Is it normal for a radiator to remain filled to the top or would you expect it to take 1/2 litre of coolant to fill to the very top or am I losing 1/2 litre per day ?

hutchy · Posted: Thu Oct 04, 2018 20:23 Post subject:

you may have had an airlock when your coolant decided to not go back into the system from the expansion tank...might be a case of jack the front as high as you can top the rad up and leave it overnight sometimes gets airlocks out Exclamation

NDZ · Posted: Fri Oct 05, 2018 12:44 Post subject:

Fair point, although its a lot of coolant to be losing from what should be a closed system. When you get back from a drive try leaving the car running and watch for drips underneath for a few minutes, it could be a leak at the next weakest link. After that it might be time to return to the head gasket - if its gone the coolant could be getting into the combustion chambers and evaporating. That was my situation a few months back, no sign of contamination in oil or water but it was bubbling at the rad neck and the head gasket turned out to be rotten. You could try the bubble test again and wait a bit longer i.e. cold start with the rad cap off and wait until the engine warms enough until coolant starts spilling over the cap. If there's no bubbles by then its a good sign, still worth checking if the oil or coolant looks in any way contaminated. If still nothing you can buy a UV trace kit for the coolant to track down a leak but loosing 1/2 litre per day I would expect you could easily see a drip.