98 XLT Heater Issue

[98ExplorerGuy]

It's been frigid in Connecticut this year with many sub-10 deg mornings; not sure if that relates to this issue but I put it out there just in case.

I drive about 22 miles each way to work; virtually entirely on the highway in the mornings and then 17 highway/5 local in the afternoon. For most of the past 10 days, I have had perfectly good heat for the entire morning commute but in the afternoon I start out with good heat which then suddenly goes cold right around the time I get off the highway. I drive to my wife's office, turn off the engine and go inside to wait around 15-20 minutes for her to finish up. The remainder of the drive home (5 miles) I cannot get any heat at all. Mind you, if I turn the temperature control to full cold, the air output definitely gets colder (well, seems like it, anyway) but on full hot it does not reach anything even remotely warm - just not ice cold.

This morning's commute was something different however. Absolutely ice cold air the entire trip until 1/2 mile from the office when it warmed up just a bit (could have been my imagination; I was quite frozen at that point).

Any thoughts as to the likely culprit, given the on again/off again episodes described above? I am particularly curious about the recent rides home where I start out with full heat and then suddenly lose it 15 miles into the drive.

I have lived without air conditioning for several summers (bad compressor) but don't think I can last the rest of this winter without heat.

 

[98ExplorerGuy]

So, I just returned from lunch - 2.2 miles each way with a 15 minute break in between.

I had full heat within the first mile starting out and again within a minute of starting the return trip.

What could be the cause of my heat working, not working, working again like this? Could I possibly have air in the system? Would that cause this sort of problem? I did have the engine thermostat and housing replaced last October, but that was a long time ago...

 

[masospaghetti]

I would bet a beer (actually a 6-pack of beers) that your heater blend door is broken. Once the door axle breaks, the door flops around inside the heater box and you get randomly changing vent temperatures. My 96 and 98 both had broken blend doors.

Dorman makes a replacement door for less than $20. The easiest way to replace it is to remove the glovebox, disconnect the door actuator from the top of the heater plenum (3 screws, be warned, 1 is a real b*tch to get to), then to cut a triangular shaped access hole in the bottom of the box using a hot knife. The old door will fall out and you can slip a new one in there.

 

[98ExplorerGuy]

I would bet a beer (actually a 6-pack of beers) that your heater blend door is broken. Once the door axle breaks, the door flops around inside the heater box and you get randomly changing vent temperatures. My 96 and 98 both had broken blend doors.

Dorman makes a replacement door for less than $20. The easiest way to replace it is to remove the glovebox, disconnect the door actuator from the top of the heater plenum (3 screws, be warned, 1 is a real b*tch to get to), then to cut a triangular shaped access hole in the bottom of the box using a hot knife. The old door will fall out and you can slip a new one in there.

Does your opinion change if I tell you that while out during lunch today I deliberately adjusted the temperature control from full cold to full hot several times and it seemed to work perfectly?

 

[masospaghetti]

Not really. I suppose you could have a partially plugged heater core, but my money is still on the blend door. The door axle is probably broken so that the actuator can still move it a little bit if the door is situated just right. It's extremely common for this generation of Explorer.

 

[98ExplorerGuy]

Can anyone point me to an engine compartment diagram which shows the location of the Heater Control Valve in a 98 Explorer with "E" engine?

Here is some additional info which I believe points to the problem being something other than the blend door:

I leave my office each day and drive about 1 mile on local roads to reach an interstate highway. From there, one of two things happens: a) I drive 16 miles and exit to local roads which I take to pick up my wife at her office or b) I drive 20 miles and then exit the highway close to my home. Note this however: immediately after the exit I would take to go to my wife's office, the highway narrows from 3 lanes to 2 and there is always a significant backup in the area which invariably causes traffic to slow from 65mph down to 15-30mph for the next two miles.

So, as I stated in my earlier post, for a few weeks now I leave work and have good (very hot) heat all the way until I exit for my wife's office OR hit the traffic jam. It happened that way again last night; within moments of hitting the traffic jam my heat went from very hot to barely warm if not cold.

I continued on to my regular exit (heat still blowing cold) and pulled into the first available parking lot. With the engine still running and heat still on, I popped the hood and felt both heater hoses at the firewall. One was just barely warm, the other was cool.

What I think is happening is that when I slow from 65 mph to 20'ish mph the engine vacuum drops and it is no longer enough to hold the heater control valve open. Maybe a vacuum system problem or maybe a problem with the valve itself.

Does anyone concur?

 

[masospaghetti]

On the Vin X (OHV) engine the heater control valve is near the evaporator box, passenger side of the engine bay, close to the firewall. I would guess all engines would have a similar configuration.

Test your theory. Hook up a hand vacuum pump to the control valve with the engine running and see if applying vacuum changes the inlet temperatures. Or, just run the engine at idle and see if the heater hose is HOT on one side of the control valve and cold on the other.

 

[crunchie_frog]

it is on the passenger side near the firewall above the fan housing. It is on one of the hoses going into and out of the heater core. Vacuum is supposed to close the valve. Provided your engine coolant is up to temp, then I think it could be: 1) faulty heater cobntrol valve which is very easy to remove and check, 2) heater core plugged and lower rpms lowers the water pump pressure and it is not pushing the water through the core which you could try a coolant flush and then hope your core does not leak. I agree with you that the cold / lukewarm hoses are a sign it is not the blend door. If it were the blend door, both hoses woud be hot when you have no heat since no or little air is passing by the heater core and removing heat from the heater core.

 

[Turdle]

Actually, engine vacuum rises at idle.

I suspect low coolant level. Park on an uphill incline, let the engine cool and take a peek inside the radiator.

 

[98ExplorerGuy]

Actually, engine vacuum rises at idle.

I suspect low coolant level. Park on an uphill incline, let the engine cool and take a peek inside the radiator.

Interesting. Shouldn't the overflow tank be low/empty then?

 

[Turdle]

Interesting. Shouldn't the overflow tank be low/empty then?

Not if it is clogged up. Sediment will settle to the bottom of the overflow, causing it to clog when trying to move coolant to the radiator. The overflow outlet is the bottom, so when coolant goes to rad it may clog.

It may allow burp, ( air out) but reclog when moving coolant to the radiator.

 

[98ExplorerGuy]

Not if it is clogged up. Sediment will settle to the bottom of the overflow, causing it to clog when trying to move coolant to the radiator. The overflow outlet is the bottom, so when coolant goes to rad it may clog.

It may allow burp, ( air out) but reclog when moving coolant to the radiator.

Very interesting indeed. The last time I looked in the overflow tank I did see what appeared to be some gelled antifreeze...

And, as I said, I did have the thermostat and housing replaced a few months ago. Perhaps the guy didn't properly bleed/fill the coolant system.

I will definitely check this tonight. Supposed to be 0 deg F tomorrow morning .

 

[98ExplorerGuy]

So, maybe Turdle wins the prize?

Had the usual problem driving home last night. I parked at the lower end of my driveway which is on a 10 deg'ish uphill climb and let the engine cool while we had dinner.

Came out an hour later, popped the radiator cap, and shone a flashlight in - it appeared to be bone dry. To make a long story short, I had to add a full gallon (!) of antifreeze mix to bring the level up to the top. Started the engine and ran it for a few minutes with the cap off then added another few ounces to top it off again and put the cap back on.

Had very good heat for this morning's drive to work even with outside air temp of 0 - 2 deg F. The real test will be to see what happens on the drive home this evening.

 

[Turdle]

Oh boy! A prize? I didn't know there was going to be prizes!

Ok, now, before your return trip home you might want to check the rad again. Need to find out if there is a leak, so when you get home try to park on a spot ( or even a large piece of cardboard) to identify if there is a leak or not.

Good luck. Hope you stay warm!

 

[koda2000]

if you had antifreeze in the overflow tank that never got pulled into the radiator, you have either a bad radiator, bad rad cap, clogged or loose hose from rad to overflow, leaking water pump. my guess is you have a bad radiator. the lost coolant went somewhere.

 

[98ExplorerGuy]

if you had antifreeze in the overflow tank that never got pulled into the radiator, you have either a bad radiator, bad rad cap, clogged or loose hose from rad to overflow, leaking water pump. my guess is you have a bad radiator. the lost coolant went somewhere.

I am going to watch for leaks and once it warms up (outside air temps; I don't have a heated garage to work in) a bit I will check the overflow hose, etc.

I mentioned above that I did see what looked like some gelled antifreeze in the overflow tank (on the sides above the "water line") so I figure maybe it is clogged a bit at the bottom outlet. Also as mentioned above, I had the thermostat and housing replaced last October and would not be surprised to learn that the mechanic didn't properly refill the cooling system - maybe he was relying on the overflow tank to tell him he needed to add more.

Anyway, I will definitely watch it for several days.