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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 21610
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Renault megane 1.9 diesel. top radiator hose cold, lower one

Customer Question

renault megane 1.9 diesel. top radiator hose cold, lower one warm and pipe to expansion pipe cold, and water in expansion pipe cold. changed thermostat as one was not fitted, takes a while for temp gauge to move, then rises quickly and expansion tank overflows. engine pressure check done and told head gasket good and pipes. holds pressure but does not pressurise system when warm. thanks. Mick
Submitted: 1 year ago.
Category: Car
Customer: replied 1 year ago.
water in expansion tank cold.
Customer: replied 1 year ago.
6 hours and no one? good job i'm not broken down........
Expert:  Matt replied 1 year ago.
Hello I'd 1st reverse flush the cooling circuit (remove top hose to rad and use a hosepipe to push water into the engine until you get clear water out of the radiator hose) and top up with 30-50% fresh antifreeze. Also check that the small diameter bleed hoses that run from the top of the radiator and the top of the engine aren't blocked as this allow the air to vent back to the header tank automatically. Also its possible the belt is slipping so its worth replacing its especially if the rubber ribs are cracked or it looks shiny on flat side of the belt - while its off check that the tensioner and other pulleys all spin freely the exception to this is the AC pump ( if fitted) I'd also suggest ensuring that you've got all the air out of the system as this sort of episode can leave pockets of air trapped and prevent the coolant from circulating properly. So check that the small hoses that run from the top of the engine and radiator that run back to the header / expansion tank are free flowing and not blocked If these are OK then remove the tank pressure cap and run the engine from cold with the heater set to full hot As the engine starts to warm, squeeze the large hoses running to the radiator to help displace any air - all the time keeping an eye on the level in the header tank, making sure it doesn't drop below the minimum and open any bleed screws built into the top cooling hoses - closing them off as soon as they start to gush water Once the engine is up to temperature the tank should be quite full. Switch the engine off and leave it to cool Then top up to the mark once its all cold and replace the cap
Customer: replied 1 year ago.
Matt, there is only one bottom hose and one top hose. the radiator has now been removed as water to the expansion tank was cold and the top rad hose cold also. rusty water came out of the engine and rad. do you thinkit is engine or rad related. thanks
Customer: replied 1 year ago.
also there was no pressure in the expansion tank even though the temp gauge rant to normal level
Expert:  Matt replied 1 year ago.
Hello I'd 1st flush the rad and the engine out with clean water and a garden hosewhats more likely is the radiator is clogged as this has the smallest passages and if its in a poor state with corroded / damaged fins then it may have to be replaced Also check that the water pump impeller / turbine isn't spinning on its shaft. You should be able to achieve this by removing the bottom hose from the engine and use a screwdriver or similar to feel for the water pump impeller blades, whilst your assistant turns the engine over by hand.If you can stop the impeller with slight pressure from the screwdriver the pump needs replacing.
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Customer: replied 1 year ago.
is it possible to be more precise. as the radiator is out, before you answered, is it likely to be the rad?, as stated, top rad hose cold, bottom rad hose warm, pipes from thermostat and oil cooler cold. or engine. I dont want to put more cash in than required. is it possible the engine is blocked by my symptons. I cannot do the test as parts are off. mick
Expert:  Matt replied 1 year ago.
Hello if you've removed the rad to replace it then you can flush that through with a hosepipe off the car - with normal mains pressure ( about 12 psi) and putting the rad on its end you should get a 'spout' of about 8" tall gushing out if its only a few inchs then its likely that the rad is blocked obviously you can't do this test with the engine block but you can flush it out with a hosepipe until the water runs clear

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