30 amp engine fuse blowing

[halbitton]

On my 99 E38, the far inboard 30A fuse in that little cream colored engine fuse holder (in the electrical box in the right rear corner of the engine bay) has blown twice. From the BMW wiring diagram website, it looks like that fuse sends power to just about every control module the car has. It also powers 6 of the fuel injectors.
The two times it has blown have always been shortly after startup (after sitting overnight) while under moderate to brisk acceleration. After replacing the fuse, I've driven the car around a bit after it has warmed up, and it seems to do OK. The last time it blew, I noticed that the motor did not quit completely, but sounded like it was lurching along on "less than 8" cylinders (maybe 2 cylinders?).
I have a peake code reader on the way, which may shed some light here, but in the meantime, if anybody has some ideas, I'm all ears.
Thanks, Hal

[motion]

It sounds like you have a intermittent short some where along that circuit. Something
that maybe is energized after startup. What number fuse is it? Just my.02

[halbitton]

It's F1 in the engine electronics fuse carrier. (There are 5 30amp fuses in that carrier).
hb

[audiavant]

The fuse blows if theres a prob w/the T Stat Plug

[halbitton]

Where is the thermostat plug...somewhere in the vicinity of the water neck / water pump?

[audiavant]

Where is the thermostat plug...somewhere in the vicinity of the water neck / water pump?

The plug is on the TStat housing. The seal goes bad, and coolant seeps thru and fouls the plug, and if you are lucky, only trips the fuse.

[darkstarmedia]

Hopefully it has not creeped into the computer and wrecked that too...

Unhook your computer connection (under the fuse box) and check for moisture... asap...

Richard

[halbitton]

Well, the Tstat plug makes sense, but how would moisture get into the computer? It's in the electrical box, which is sealed and, as far as I know, there are no coolant lines that run through there. Anyway, everything in there is nice and dry.

Back to the Tstat...if that is indeed what is blowing the fuses, would the bad actor be the actual thermostat valve, or can the receptacle be changed separate from the valve?

[Mayorchuck]

The coolant leaks thru the seal as mentioned. Plug is usually burnt and coolant follows the wiring into the Ebox. Has happened to many here.

[Timm]

Unbeliveably, the coolant wicks up the loom!

[halbitton]

Wow, I had no idea that was possible...remember that 3 stooges episode where they had water spraying from the light fixtures...

So is that thermostat plug receptacle part of the thermostat housing, or separate?

[KGB7]

Thus BMW changed wiring design on newer e38's and this is no longer an issue.

[halbitton]

Thanks guys, I found it...
when I removed the MAS duct, there was the thermostat plug, just hanging there. The receptacle had broken off flush with the housing, and was still in the plug, as if it had been bumped and sheared off. Looks as if it has been that way for some time. When I pulled the remains of the receptacle out of the plug, it was all pristine and dry. Apparently that thermostat defaults to open when it doesn't get a signal.
Now to order a new thermostat/housing.
thanks, hal

Which begs the question, can I drive it while waiting for the new part to arrive. It appears as though it's been running that way..., only blowing that fuse when the broken receptacle contacts bumped against the housing and shorted out. It even gets up to op temp OK (dead center on the gauge). What do you think?

[IcemanBHE]

Dont know why not...as thats how its been for a while. As long as it doesnt short out any more....

[KGB7]

If the thermostat wont open then your engine wont cool propelry because coolent is not being circulated.

Just because temp guage shows your temp is normal it doesnt mean engine is not over heating. Since fluid is not circulating properly, fluid is hotter in some parts of the engine then other parts of the engine and cooling system.

Dont drive till you get it fixed!!

[SirReal63]

It fried on my 2001, big time but fortunately did not take out anything else.

[halbitton]

Bear in mind that even when the thermostat is not open, coolant still circulates throughout the block...it just bypases the radiator instead of going through it. Also, aluminum and coolant are very efficient conductors of heat...that fact, and the aforementioned circulation will ensure that the temp will equalize throughout the motor...if that thermostat was not opening, the temp guage would peg to the high end.

Can anybody state for a fact that the thermostat on this car is electrically controlled. From the pics on the parts websites, it almost looks like it could be a combination electrical / temperature (expanding meduim in a copper vessel) controlled.

[KGB7]

Bear in mind that even when the thermostat is not open, coolant still circulates throughout the block...it just bypases the radiator instead of going through it. Also, aluminum and coolant are very efficient conductors of heat...that fact, and the aforementioned circulation will ensure that the temp will equalize throughout the motor...if that thermostat was not opening, the temp guage would peg to the high end.

Can anybody state for a fact that the thermostat on this car is electrically controlled. From the pics on the parts websites, it almost looks like it could be a combination electrical / temperature (expanding meduim in a copper vessel) controlled.

If it bypasses the radiator then its not being cooled. Thus it over heats. Other wise there would be no need for a radiator.

Radiator is the only thing that cools the coolant fluid.

Dont over think it. Just dont drive the car till you get it fixed.


p.s.

If your temp gauge is showing 1/4 of the temperature, then you know for a fact that the thermostat is always open.

If the temp gauge is at 1/2, then its closed or working properly. If its closed and still showing 1/2 then your engine is over heating.

[halbitton]

I realize it's not being cooled if it doesn't go through the radiator. My point is that by circulating even when the thermostat is closed, there are no hot spots in the coolant...it will heat evenly throughout the block. Even so, the temp probe may not be situated in this loop, so you may be right.
Best regards, Hal

[SirReal63]

There is a difference in an electrically assisted t-stat and an electrical one. Ours is electrically assisted, it is a regular t-stat otherwise. After my incident I created a new plug and it worked fine, though many people here said to just leave it unplugged. When I replaced my cooling system a month ago, I just left the wired un-attached and have had no issues. The electrical assistance, as I understand it, is to aid the engine in getting to temp sooner, but makes no difference in the actual operation of the 220 degree t-stat otherwise. As long as the t-stat is opening as it should at 220 degrees, there is nothing to worry about.

[Timm]

The thermostat is essentially a 105C thermostat when no power is connecetd to it - this is the temperature that the engine runs at when cruising, this increases fuel economy. When more power is needed from the engine, the coolant temperature needs to be lowered to stop detonation (pinging or knocking).

The electrical connection to the thermostat is connected to a small heater inside the thermostat - applying power reduces the temperature at which the thermostat opens to 85C. This is called characteristic-mapped cooling.

With no power to the thermostat your coolant will always be regulated at 105C - which is fine for economy, but does not allow full power to be achieved.

Full information here:

http://www.meeknet.co.uk/e38/E38_Map_Thermostat.pdf