Coolant over flows - Volvo Vehicle Parts & Accessories

Check and see if the cooling fans are coming on. Check fuses and relays for them.

I would want to check coolant flow into the radiator, if possible. Does your radiator have a cap, can you stick your finger way down in the coolant, cold engine. Some cross-flow radiators you can drain the coolant down far enough to see the top two coolant passages. Then with thermostat removed and everything hooked up, the coolant flow is instant, when you crank it. Sometimes I do this just for testing. If no coolant flow, have to check water pump and belt. I can't tell from here if there might be blockages in the engine coolant passages?

What you are describing is a lack of coolant flow in the engine or radiator, or lack of air flow thru the radiator.
If you are sure the coolant level is ok, and flow is good, I would check for a restriction in air flow thru the condenser and radiator.

coolant will not flow from the return pipe continuously.when the engine heats the coolant expands returns to tank. coolant fan starts engine cools down return pipe flow stops . fan stops after times, again coolant heats up and flows through the pipe. this cycle continues and go on.

WAIT UNTIL YOUR ENGINE IS COLD,YOUR RADIATOR PRESSURE CAP IS LOCATED ON THE COOLANT OVER FLOW RESERVOIR, THATS WHERE YOU ADD COOLANT WHEN COOLANT LOW,YOU POUR COOLANT IN THE OVER FLOW RESERVOIR UNTIL COOLANT LEVEL REMAIN AT FULL COLD MARK DONT OVER FILL OVER FLOW RESERVOIR, WHEN COOLANT LEVEL STOP DROPPING WHEN ADDING COOLANT AND COOLANT LEVEL STAY AT COLD MARK ON THE RESERVOIR YOU RADIATOR HAS THE CORRECT COOLANT LEVEL IF COOLANT LEVEL KEEP DROPPING CHECK FOR COOLANT LEAKS AROUND RADIATOR AND THE TOP AND BOTTOM RADIATOR HOSES, LOOK FOR COOLANT LEAK AT WATER PUMP GASKET OR SEAL OR LEAK AT WATER PUMP WEEP HOLE IF YES REPLACE WATER PUMP.

One of two things: 1)Heater core may be plugged - on most vehicles you can switch the heater hoses around to reverse the flow of water to try to remove the blockage. This will be a temporary fix however because the foreign material will be in the coolant system and will eventually plug the core again. If you try this and it helps I would suggest flushing the coolant system to remove any loose material. 2)Failed water pump - Sometimes the impeller on the water pump gets corroded to the point where it will not move the coolant correctly. The solution for this is to change the pump. You can do some troubleshooting buy A)draining enough coolant from the system to drop the level below the upper of the two heater hoses B)remove the upper heater hose on the engine end and position the open end higher than the engine, allow coolant to drain to the point where it naturally stops C)Have a friend start the vehicle breifly and see if coolant flows from either the hose or the fittting it was connected to. If coolant flows from the hose, the core is not plugged. If coolant flows from the fitting, the water pump is working. If coolant doesn't flow at all, try switching the ends on the core if possible and repeat test. If the coolant still doesn't flow, you probably need a water pump.

One of two things: 1)Heater core may be plugged - on most vehicles you can switch the heater hoses around to reverse the flow of water to try to remove the blockage. Yhis will be a temporary fix however because the foreign material will be in the coolant system and will eventually plug the core again. If you try this and it helps I would suggest flushing the coolant system to remove any loose material. 2)Failed water pump - Sometimes the impeller on the water pump gets corroded to the point where it will not move the coolant correctly. The solution for this is to change the pump. You can do some troubleshooting buy A)draining enough coolant from the system to drop the level below the upper of the two heater hoses B)remove the upper heater hose on the engine end and position the open end higher than the engine, allow coolant to drain to the point where it naturally stops C)Have a friend start the vehicle breifly and see if coolant flows from either the hose or the fittting it was connected to. If coolant flows from the hose, the core is not plugged. If coolant flows from the fitting, the water pump is working. If coolant doesn't flow at all, try switching the ends on the core if possible and repeat test. If the coolant still doesn't flow, you probably need a water pump.

BLEED AIR OUT COOLANT SYSTEM.WAIT UNTIL ENGINE COOL DOWN.REMOVE COOLANT OVER FLOW PRESSURE CAP.IF YOU HAVE 3.1 OR 3.4 ENGINE OPEN AIR BLEED SCREW ON WATER PUMP BYPASS HOSE.OPEN BLEED SCREW.WATCH COOLANT IN OVER FLOW AS YOU OPEN BLEED SCREW COOLANT WILL DROP IN OVER FLOW JUG. AS IT DROPS CLOSE BLEED SCREW ADD MORE COOLANT IN OVER FLOW JUG DO THIS UNTIL COOLANT LEVEL STAY AT COLD FULL MARK.WHEN DONE TIGHTEN BLEED SCREW DONT OVER TIGHTEN IT OR IT WILL STRIP OUT BREAK.CRANK CAR UP UNTIL THERMOSTAT OPEN THAT WHEN TOP RADIATOR HOSE GET HOT.WATCH COOLANT GAUGE,IF ENGINE TEMPERATURE RISES TURN OFF ENGINE WAIT UNTIL COOL.REMOVE RADIATOR PRESSURE CAP USING A RAG TO KEEP FROM GETTING HANDS SCALED.ADD MORE COOLANT IF NEEDED WHEN ENGINE COOLANT STOP DROPPING IN OVER FLOW JUG AND ENGINE DONT OVER HEAT AIR IS OUT OF COOLANT SYSTEM.

The heater is only working when the coolant flowing into the heater core ( matrix). It seems that there is no coolant flowing into matrix in your case. It is [possible that the valve to control the coolant flow is not operated so no coolant can flow through. HAve you check that valve. If you did confirm that is working then the next thing is to check if there is coolant at the incoming hose connecting to the heater matrix. At the fire wall there is 2 rubber hoses going to the heater matrix. Try to identify them at the firewall and trace them back to the engine. Buy a piece of the clear hose then connect it into the place of the other 2 ends so you can see if coolant flow when you turn the car at idle. This is to confirm that there is no blockage in the water jacket. To recap check if there is no coolant blockage at the incoming hose to the heater matrix. Hope this can help you to find the root cause.

Check the system is properly filled with coolant, bleed off any air locks as specified by manufacturer.
Allow motor to warm up above thermostat opening temperature before checking for coolant flow- check for operation of heater/demister- if it produces warm air you do have coolant flow.