HI, Vehicle had no heat and was overheating, so we had the heater core flushed - twice. Didn't help. We changed the heater core and thermostat. Now vehicle is still overheating. What else do we check?

If the heater core hoses are hot but there is no heat coming out of the vents, and the vehicle is also overheating, there are several possible issues that could be causing this problem. Here are a few things to check:

1. Coolant level: Check the coolant level in the radiator and reservoir. If the level is low, it could cause both the overheating and lack of heat. Top up the coolant to the correct level and check for leaks.
2. Thermostat: If the thermostat is stuck closed, it could be preventing coolant from circulating through the engine and into the heater core. This could cause both the overheating and lack of heat. Consider replacing the thermostat if it is found to be faulty.
3. Water pump: The water pump circulates coolant through the engine and heater core. If the water pump is not working properly, it could be causing both the overheating and lack of heat. A mechanic can test the water pump to determine if it is functioning correctly.
4. Heater core blockage: If the heater core is clogged or blocked with debris, it can prevent hot air from circulating through the cabin. This could cause a lack of heat. Flushing the heater core may help remove any blockages.
5. Cooling system blockage: A blockage in the cooling system, such as a clogged radiator or hose, can prevent coolant from flowing properly and cause overheating. Have a mechanic inspect the cooling system to determine if a blockage is present.

These are just a few possible causes of the overheating and lack of heat. It is recommended to have a qualified mechanic inspect the vehicle to diagnose and repair the issue.

Re-flush the system again, I know but it's best you do. Buy a lower degree thermostat and see how it does.

If you have no problems with any valve or perhaps the heater blower motor then heater core could be plugged, I have back flushed some successfully by changing the flow of coolant backward and catching back flow in a separate container. Could actually see large amounts of coolant stop leak.
1st thing to check, is coolant level full.
2nd , is the blower motor actually blowing,
Traveling down the road causes ram air to push through the heater as long as the controls are set for fresh air intake.
Remember If allumaseal will not plug a leak then more professional measures must be used. Many radiator stop leaks are so effective like bars leak the stuff that looks like rabbit feed pellets that when used professional help must be found because the radiator no longer has the circulation ability to cool the engine and if a vehicle is run any at all above max operating temperatures it will normally result in costly repairs. I have personally used fine ground black pepper and had good results but it must be very fine ground no matter what is used it must be small enough to travel through the small tubes of the radiator and or heater core. If larger particles are used coolant flow will probably be restricted enough to cause either no heat in the cabin or overheating of the engine which most certainly can cause serious damage the very first time.

the stuff describe most likely from the anti boil -anti freeze mixture that has become ineffective for not being changed regularly and not up to percentage to do the job. It allows the aluminium parts of the car to corrode and what you see is the end result . It will deposit in the cores of the radiator and block them up resulting in a replacement radiator . You can expect corroded aluminium parts from all areas of the motor.

Possible, with rad cap off, let vehicle idle until coolant fan comes on then shut vehicle off for 30 minute cool down. Top up rad, install cap and drive and recheck heater operation and any overheating.

Is it ACTUALLY overheating? Check for heat at the top and bottom radiator hoses, and at both heater core hoses. If one is cold then your radiator or your heater core may be plugged and in need of a individual flush.

No a heater core alone will not cause a vehicle to overheat. The heater cores sole purpose is to transfer heat generated by the engine to the blower motor so that you can get heat from your car vents. A person could technically remove the heater core from the vehicle and connect the hoses together to bypass it, and the car will run as if nothing happened, minus the lack of heat in the vents.

If the car is overheating, there are three mai issues that could be happening. 1) The radiator is blocked and not allowing coolant to be cooled off before returning to the engine.
2) The water pump is broken. The engine relies on this pump to move the coolant throughout the engine. It may not leak as long as the gasket is alright but the impeller ( small fans on the inside of the water pump ) could not be turning.
3) Lastly and most commonly is a faulty Thermostat. The thermostat is the valve which opens and closes at certain tempuratures and decides if hot coolant stays in the engine or circulates to the radiator to be cooled off. If the thermostat fails, unless you have a failsafe one, will fail in the closed position keeping the hot coolant in the engine and causing it to overheat.

The thermostat is by far the cheapest of the issues so consider changing that first along with a coolant flush before considering putting a new rad or waterpump. You can usually get a thermostat, 2 jugs of coolant and a flush kit for about 50$ at pretty much any parts store. Becareful however not to drive a overheating vehicle as gasket burning and head warpage can occur, which will require rebuilding th head.

Good Luck

Air in the system , bad water pump , cooling fans not working ! Maybe you should take to a shop ?

Your engine is overheating because the coolant is not flowing properly. If you have clogs in the cooling system changing the thermostat is not going help very long. Depending on what the material is that's causing the clog it will eventually prevent your new thermostat from working as designed. Buy a radiator flush kit and flush the system. If your heater core is clogged it may prevent heated water from entering it (that is where the heat is radiated from).

will it sounds like u tryed everything except what could be cousing the problem it is probley the heater core is pluged with hard water or calcium build up or is just pluged and a rad flush wont flush the heater core unless you start the vechial and flushing the rad to do the heaterd core to turn on the heat to high and the fasters fan speed and make shore the van is running.