I have a 1998 Ford E350 Motorhome with the 6.8L V10. After coming out of the Hills in West Virginia the Temp gauge went to HOT and started running in the fail-safe mode. Coolant levels are fine. I took it to the nearest Ford Dealership, on a test drive their Computer/Scanner says Coolant Temps are good, but it still goes into fail-safe mode after 2 mile under slight load. Turning the key off and On resets it. They changed the sensor near the intake manifold with with the same results. What could be wrong? The engine is strong before cutting out the 5 cylinders. Anyone ever experience this? the dealership has no clue it seems.

Thanks,
Scott

 

Few questions...

1. Does the coolant boil over?

2. Does the fan clutch engage?

3. When the dealer's scan tool said the temps were normal, was the truck running in fail-safe mode?

 

1. The very first time it happened it did look like some of the coolant had come out of the resevoir, but I only had to add about a quart of coolant to get it back to the levels.
2. The fan appears to be running fine, however I did not shut off the engine and watch to see if it free wheels.
3. The water temperature in Fail-safe mode was normal, and I think that it was the temp sensor in the head the machanic said was reading 140 degrees celcius.

I unplugged the water temp sending unit on the front of the engine. This made it so the gauge did not work, but I still had the same results with the Temp light coming on and it going into fail-safe mode.
One thought I had, was I had pulled the top hose and cranked it over to see if it was pumping water, and it was. It seemed as though after that I didnt really have to add a lot of coolant back into the system. If it was low on coolant the resevoir would be empty? and deffinately the temp while operating would be higher?

 

On the 6.8 there are 2 sensors. The Engine Coolant Temperature sensor is in the intake manifold. The Cylinder Head Temperature is in the driver's side head, almost under the intake manifold. That is the one that tells the PCM to go into fail safe mode.
140C (284F) is way too hot. If it was really hitting 140C it would be boiling over. I think you probably have a bad CHT sensor.

 

Just got off the phone with the Mechanic. Yesterday they changed the CHT sensor, still having the same problem. They are on the Phone with Ford and Ford is saying it is most likely a 1 of the 10 coils. Today he said that the ECT and the CHT had the same temp reading of 220F. Oh man this is gonna cost me for them just swapping out parts.
Im home in Indiana the Motorhome is West Virginia.

Racerguy? Drag Racer?
Thanks so much for helping out,
Scott

 

Nope I race around in circles

 

I believe you have one of 2 problems. The only reason that the overflow would be full is if the cooling system is incapable of pulling it out. If the coolant levels are fine, then it's not a vaccuum leak (a quick pressure test could confirm that). I believe that you problem may be as simple as a stuck thermostat. They're relatively cheap to replace and could save a lot of time and headache down the road. Hope you find out the problem.

 

I failed to mention that the first thing the Service department did was change the thermostat. sorry. I do keep feeling like that it might not be pulling in the coolant from the overflow, but today the mechanic said the temp readings are 220F on the ECT and the CHT?

 

I called the Service Department. Using Ford's advice they have checked every coil on it and they are all good. Now they have a computer on order.
So far they have replaced:
1. Thermostat (didnt do a pressures test afterwards)
2. CHT sensor (says the readings are 220F when operating now after changing it)
3. Checked every Coil

Could this problem be the Computer? The dealer says that this is good for me because it will be under warranty. (1998 E350 27,000 miles) Is this true? How about all the troubleshooting they have done up till now? Is that going to be warrantied?

Thanks,
Scott

 

Since all the "mechanic" stuff has been replaced with known good parts, the next thing to suspect would be the PCM itself.

Troubleshooting is warrantied.

 

Bad news for me.... The PCM didnt fix it.

So far they have replaced:
1. Thermostat (didnt do a pressures test afterwards)
2. CHT sensor (says the readings are 220F when operating now after changing it)
3. Checked every Coil
4. PCM

 

Scottyp, any luck on solving the problem? I seem to have the same problem.

Thanks, Mark

 

I've been meaning to get back on here and post...The dealership talked to Ford and they told them to move the CHT sensor from the Left head to the Right. That seem to fix it. The mechanic told me that I need to flush my cooling system. There was only an 8 degrees difference from left head to the right but that was enough to trigger the computer into safe mode. I still feel like we fixed the sympton and not the problem. Here pretty soon I'm gonna flush the system real good and hookup the left CHT sensor. The Mechanic left it in there for me. You might try just adding a sensor in the right head and hooking it up. I ended up with a bill over 500.00 for this simple swap, but I got my motorhome home finally. let us know what you find out.

 

Just guessing but it sounds like it may be a head gasket. If the head is leaking it will cause increased coolant preasure. I am sensitive to blown head gasket since I just blew one on a 98 class c. My first indication was the odor of coolant as I was comming out of the mountains.
Just a thought, hope it was just the sensor.
john.

 

hey scottyp
when you find out what was the problem please let us know.....a fellow class c owner