Two months ago my front heater core sprung a leak. I installed a new one and hot air was once again flowing. Last week the engine over heated after approximately five miles of driving. It literally maxed out in the red. The cabin air, turned up to 90, blows ice cold in both the front and rear. I replaced the thermostat and then noticed the radiator sprung a leak. After replacing the radiator (and hosing out the block) the engine is still running hot. It now runs close to H but does not max out anymore. But I have to admit that I haven't tried to push it to its limit. The lower hose was also replaced. The "quick" disconnect is forever stuck to the old radiator.

A short drive from a cold engine heats it to near H. However, The engine will not over heat when first turned on from cold and left to idle. 30 minutes of idling does nothing more than bring it up to operating temperature.

I have done a block test to determine if any exhaust is leaking into the reservoir and the test came up negative. I have checked the water pump for leaks and removed the belt to feel if the bearings were shot. The water pump seems fine. The upper water return hose gets scalding hot and does not collapse when squeezed. The heater core hoses both heat up to approximately the same temperature, but neither gets very hot. The fan does not turn freely and has some (little) resistance when turned by hand. I've tried to burp the system with no definitive results. The reservoir has not been running dry.

After a short drive, with the engine running near H, I cracked the seal on the overflow reservoir and before the water bubbled out I sealed it back up. Almost immediately after this the water was sucked back into the radiator and the gauge read normal for engine heat. The cabin air still blew ice cold.

I'm perplexed as to what all of this could mean. I'm not sure if my next move should be replacing the water pump/fan or if I should be looking for a clog in the system. Any advice?

1999 Expedition
5.4L 2WD
Closed cooling system

 

They are "quick" connect fittings, not "quick" disconnect fittings. You've got to read the fine print.

As to the overheating two things stand out as possibilities. One, the impellers on the water pump are gone so the flow is just not there. Two, you have a blown head gasket. A blown head gasket tends to pressurize the system and force coolant out the overflow. Since you didn't mention that was happening I've put it as the #2 possibility instead of the #1.

 

I've done a combustion leak test and the liquid remained blue. Would this be enough to definitively rule out a blown head gasket or cracked block? I'll pull the water pump and inspect it.

 

Yeah, pretty much.

 

I suppose I should clarify that in the context of overheating this test would rule out a blown gasket. Thanks for the quick replies. I'll report back with my findings after I pull the water pump.

 

Thar be yer problem!



Broken water pump

Everything works now as it should with the cooling and heating system. Thanks for the reply!

 

Chalk up another one in the win column.