Diagnosing overheating from 200 miles away

[Whoop92]

Hi All,

Here's what my quiet weekend turned into. My spouse drove our '99 5.4 Expy with about 160k miles to visit relatives about 200 miles away. On the way there it started overheating. By adding about 1.5 gallons of coolant and turning the cabin heat on high it made it to the relatives' house.

That's all the info I have. There is a leak somewhere but I don't have any information on where it is coming from. I can't remember when nor if the water pump or thermostat have been replaced.

Obviously, there is a problem and I'm currently planning to visit the relatives to fix the Expy. I'm trying to figure out what the most probable problem is so I take all the needed tools and parts.

Full disclosure, about two months ago it overheated on a road trip with my daughter. The car store scan tool said it was a bad thermostat but the local kind mechanic said that it was the very low oil that hadn't been checked like it should. Oil was added and the truck didn't have any problems for the rest of the road trip. No heating problems since then until now.

My hopeful guess is that the thermostat is busted.

My probable guess is the water pump has finally given up the ghost.

My nightmare is that there is something else wrong that I can't figure out.

What say y'all? Any ideas on what else could be wrong or tips on how to diagnose or fix these items?

Thanks for your help!

 

[whtbronco]

Unfortunately there is a myriad of tools that might be needed. With the age it could be a hose, the radiator, intake manifold, the water pump, heater core, if you have auxiliary rear HVAC it could be leaking back there.

If it's the water pump it would likely have been leaking for quite a while to be 1.5gal low.

At the very least bring a ratchet, set of metric sockets, some extensions, set of metric wrenches, pliers(slip joint if available), screwdrivers, sandpaper, wire brush, a drain pan, jack and jack stands, wheel chocks, cordless light, telescoping mirror, hand cleaner, rags and maybe something to lay on.

Also bring some coolant and from the sounds of it some motor oil.

 

[Whoop92]

I've got the auxiliary rear HVAC. In fact, the heater core for the front HVAC system was replaced in November and worked like a champ in very cold weather over the past winter. The rear HVAC has been running fine and hasn't been messed with yet.

I haven't seen any puddles under the Expy in the past couple of months. It's only been driven on occasional grocery store runs during that time. On those short drives I haven't smelled any coolant in the cabin.

 

[whtbronco]

I've replaced my water pump 3 or 4 times now and never had coolant on the ground. It just sort of burns off or blows away.

Coolant leaks may only be present while it's running since it's under pressure and if there's a leak the pressure will dissipate pretty quickly. As a result you may not have much if any coolant on the ground. Course if the coolant is getting sucked into the engine there won't be any on the ground either.

 

[JerrySLC]

The other thing to consider is the spark plug coils. I’ve had to replace about half of them, and the symptom is overheating. You would see some codes about cylinders misfiring. I also had to flush the cooling system and change the thermostat.

 

[tekrsq]

Oh, this brings back memories. My 99 EB 5.4 overheated about 3 yrs ago....with about 180,000 on it. After replacing the t-stat, radiator, and a coolant flush, it was still running warm. When I pulled the water pump, I discovered ALL of the fins were completely gone. They had rusted off. Even after replacing all that, it would still run warm (just below the hot mark), and a miss at idle anytime the ambient temp got over about 85F. After multiple shops could not diagnose the issue, a VERY old school mechanic told me the head was cracked....even though it never had any type of fluid exchange between the oil and water. He said it was very typical of the 5.4's after overheating, and would eventually fail. I nursed it for a while, but he was right. It eventually (within about 5-6,000 miles) started to constantly run hot. After discovering the small ransom it costs to replace the head, I eventually just decided to replace the engine with a reman unit. Needless to say, I was curious about if a head was actually the cause, so I had the heads checked, and sure enough, the passenger side head was cracked between the 2 rear most cylinder.

I hope your issue is a simple bad t-stat or water pump, but if your engine got seriously hot, I'm afraid you could possibly have a bigger issue now. Good luck !!!!!!

 

[Whoop92]

JerrySLC, the spark plugs and coils were replaced back in December 2020. I had no idea that their way of going bad was to overheat the engine

Tekrsq, you're scaring me. I hope that I don't go down the same path as you but thanks for giving me a head's up about it.

The Expy made it home under its own power -with the heater on- and no apparent loss of any fluids. The 'service engine soonn' light came on at the beginning of this saga but went out about halfway through the trip home.

I just turned the ignition on and the 'service engine soon' light stayed on. I just put my scan tool across it and these are the codes that seemed relevant:
P1299 - Cylinder head overtemperature protection active. DTC Severity 2 of 3. Repair immediately if drivability issues are present. Threat to essential system components if not.

P1285 Cylinder head overtemperature detected

U1073 - Engine Coolant temperature data invalid


The rest of the codes were:
P1000 - OBD systems readiness test not complete

C1107 - ABS function enabled input circuit failure

B1894 - Wiper rear motor speed sense circuit failure

B1202 - Fuel sender open circuit

 

[Whoop92]

Is there any way of determining if the thermostat or water pump or whatever else is the problem before I start tearing into it? Or is this just a case of swapping parts until it seems to work right?

 

[whtbronco]

Yes. For the water pump look for a chalky white line from coolant dripping from the weep hole and running down the front of the block. If it's really bad you be able to grab the fan clutch shaft and move it other than just rotation.

Thermostat, if it heats up and then doesn't stabilize, but rather keeps heating up the thermostat may be stuck closed or the fan isn't working. If the thermostat is stuck open it will take a long time to warm up and may run a bit cooler than normal.

Since it was 1.5gal low on coolant that may have been why it overheated, but you'll need to figure out where the coolant went.