I might have made a mistake

A few months back I decided to save money, and instead of buying a new car (which we really can not afford right now) I bought an E39 with 100k. The 98 528/5 is a great car and fits our life wonderfully but Bmw's are starting to look and feel alien to me; the other day, after a few thousand mile trips Janet drove down to her sisters house a few miles away and on the way home the cars temp gauge decided to go all the way right and the red overheat light on. All this for no apparent reason. I took the car out the next day and same thing. I couldn't find anything wrong with the motor; no overheat symptoms at all and nothing to do but limp in to my friends shop and let him do a leak down test (I don't have the tool ) and let him fool with it. I thought maybe the temp gauge sensor had gone bad or lulu blew a headgasket.

This is what happened;

Jack put a reader on the car and one of the codes it spit out was the coolant
sensor. What that means I don't really know but... He then put some kind of
reader on the gauge sending unit and it was reading hot. After it cooled off
jack did a leak down test and everything tested out fine. He then took the water
pump off and there was no coolant behind it (his words) so after making sure it
was the metal impeller type pump he reinstalled it, filled up the cooling system
with new stuff and bled it out and everything went back to normal, tested out
perfect.

I guess I'm to assume the block had an air lock that might have caused this
episode. I don't have a clue why or how that could have happened but I guess
there's a few things I have not experienced in my 67 years so far!

Okay, so far the car has been perfect and after I took about a quart of coolant out of the upper tank on delivery (what are these guys thinking and where is the coolant going to go after it heats up- Don't overfill sealed cooling systems!) the car has really seemed fine But I still don't trust it.

I guess I'm just a luddite that should have stayed with the 2002. These newer cars make me feel useless, dam it

Cheers, Rick

If the car passed a cooling system pressure test, you should be good to go. I think the E30 needs the coolant system bled of air after refilling it. FYI, on my wife's PT Cruiser, the car overheated, turned out the cause was the electric fan on the radiator which was supposed to go on when the temp rose to a certain value. (engine is mounted sideways so there is no fan on the belt system) The fan turns off when the car reaches 35 mph (the idea is that the forward motion of the car will allow enough air over the radiator such that a fan assist is not needed).

Out of curiosity, how is the fan on the car, has the viscous coupling gone south?

As car design evolves, you just have to know where the bodies are buried.

alan

Well, that kind of failures is really annoying, but any car will do something like that.

My 323i overheated the first trip to my parents (my mother: "told you the car was to old to be good!...") and several times after, only cured it with the complete set of tubes, new expansion tank and cap, viscous coupling and the third coolant refill and bleed. By then I knew all there was to know about the e30 cooling sistem.

The old Citroen GSA caught on fire at the highway and burned to the ground, after I gave it a new exhaust system, battery and all new fluids and filters.

The Citroen BX, once in a very hot day spilled all the new coolant water to the floor, because it is wired so the electrical fan turns off with key off, and the car was very hot when i turned it off. It leaked the green hydraulic fluid countless times, and it costs like 9€/L!

The Mercedes Benz failed on the inaugural trip, had to be towed home. It simply wouldn't pull in any gear, turned out on half-shaft was disconnected from the wheel somehow.

Be cool, no car is perfect!

Are you sure water is being pumped around? Might be it is clogged somewhere. What height is your water pump located relative to the engine block/head? Usually there should be water to be found 'above' the pump level, I'd be surprised your had run out of water that much. If ever your engine was filled with anything else than good coolant, it might have got clogged.

Last weekend I had to re-pressurize our central heating system since I had removed one of the radiators. Opened the valves, no water running. Checked the no return valve, OK. Turned out to be a T-connection had become clogged, allowing water to go straight through the T but not letting it in the other part.

Our E-38 has a similar cooling system. There will probably be a crack in the tank where the pressure sensor is. It lets the coolant out and if the sensor has failed as they can do...you will be out of coolant. The coolant can also sneak out of the cap is it is not tighened correcly...ask me how I know that. Also, the vent screw near the cap must be opened when filling to allow air out of the system. It cannot let air out any other way.

The tank can be full but the rest of the system may have a lot of air in it. The air must be vented.

I changed the tank myself as it was not difficult. There is a connector on the bottom of it for the sensor. Have to take the air filter box off and the MAF. Drain the coolant by removing a hose or something. There is a hose on the bottom of the tank that will be difficult to use to drain the system and capture the fluid. The air vent screw holds the tank in place most likely.

Bob in Lake Havasu

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alanrw
If the car passed a cooling system pressure test, you should be good to go. I think the E30 needs the coolant system bled of air after refilling it. FYI, on my wife's PT Cruiser, the car overheated, turned out the cause was the electric fan on the radiator which was supposed to go on when the temp rose to a certain value. (engine is mounted sideways so there is no fan on the belt system) The fan turns off when the car reaches 35 mph (the idea is that the forward motion of the car will allow enough air over the radiator such that a fan assist is not needed).

Out of curiosity, how is the fan on the car, has the viscous coupling gone south?

As car design evolves, you just have to know where the bodies are buried.

alan

Thanks Alan, First off the fan clutch is in good shape, and this overheating condition happened at speed so even if it was bad or not 100%, the gauge would not have gone up as it did (rather fast and straight over to hot setting the overheat red lamp light on/in the gauge).

The external fan works (the one in front of the radiator) but I did not think to turn the ac on when I saw the needle go nuts and I did not think to turn the heater on either

The weird thing is, now that I'm driving the car again, I do not have any reason to think it won't happen again (overheating on the gauge) And to make matters more uncomfy there's no reason to think (other than the gauge) it overheated in the first place; the car was never low on coolant and never gave any signs of sounding or acting like it was hot, no steam, no nothing!

I really thought it was a bad sending unit for the gauge...

Rick

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Michiel 318iS
Are you sure water is being pumped around? Might be it is clogged somewhere. What height is your water pump located relative to the engine block/head? Usually there should be water to be found 'above' the pump level, I'd be surprised your had run out of water that much. If ever your engine was filled with anything else than good coolant, it might have got clogged.

Last weekend I had to re-pressurize our central heating system since I had removed one of the radiators. Opened the valves, no water running. Checked the no return valve, OK. Turned out to be a T-connection had become clogged, allowing water to go straight through the T but not letting it in the other part.

The water is pumped through fine I think Michiel, when Jack took the pump off it was the good type with the metal impeller and the pump is located about where the M20 is. Don't forget, these M50-52 motors are evolutionary not revolutionary. I'm sure there was lots of coolant above the pump; the overflow tank was filled, when hot and cold. I don't think I've got a clog either.

I just put a new bathroom in the house and had to take the radiator out to restore it, everythin had to drained and refilled and all the radiators had to be bled out. It was all very easy.

Rick

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Bob in Everett
Our E-38 has a similar cooling system. There will probably be a crack in the tank where the pressure sensor is. It lets the coolant out and if the sensor has failed as they can do...you will be out of coolant. The coolant can also sneak out of the cap is it is not tighened correcly...ask me how I know that. Also, the vent screw near the cap must be opened when filling to allow air out of the system. It cannot let air out any other way.

The tank can be full but the rest of the system may have a lot of air in it. The air must be vented.

I changed the tank myself as it was not difficult. There is a connector on the bottom of it for the sensor. Have to take the air filter box off and the MAF. Drain the coolant by removing a hose or something. There is a hose on the bottom of the tank that will be difficult to use to drain the system and capture the fluid. The air vent screw holds the tank in place most likely.

On the 528 Bob I think the only bled screw is on the thermostat housing. The thing is I just made two trips with the car, both over a thousand miles each and nothing happened. If I was having even a small air lock somewhere I think it would've shown itself somehow/where.

I've started driving it again but have this fear all is still not cool. I'm going to try another trip up to Vermont in a few days so we'll see what happens!

Thanks for all the input guys, Rick

Another thing to keep in mind is that the gage in the instrument cluster does not tell you what the temp is...when centered, it says it is in the normal range which can be quite large. Once it gets outside that range, it immediatly goes full over hot. That is what happened to me when the coolant was low. The coolant sensor indicated low in a message but efforts to limp home caused it to go out of range hot very quickly.

Also the thermostat might be a computer controlled mechanism that tries to regulate the engine temp to optimize perfomance. While cruising, it will raise the temp to about 210F. If the temp sensor is a bit off, it could think the temp is out of normal range.

On my E-38 the computer control was not working and the mechanical override was making the engine run at max temp most of the time. It was "only" an $80 or $90 part I think.

Bob in Lake Havasu

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Bob in Everett
Another thing to keep in mind is that the gage in the instrument cluster does not tell you what the temp is...when centered, it says it is in the normal range which can be quite large. Once it gets outside that range, it immediatly goes full over hot. That is what happened to me when the coolant was low. The coolant sensor indicated low in a message but efforts to limp home caused it to go out of range hot very quickly.

Also the thermostat might be a computer controlled mechanism that tries to regulate the engine temp to optimize perfomance. While cruising, it will raise the temp to about 210F. If the temp sensor is a bit off, it could think the temp is out of normal range.

On my E-38 the computer control was not working and the mechanical override was making the engine run at max temp most of the time. It was "only" an $80 or $90 part I think.

Thanks Bob, what motor do you have in the 7, V8 or 12?

It is interesting how that temperature gauge works, it's not like a normal system. I've been told Bmw went to that kind of system because they were getting a lot of complaints from customers because their motors were showing a little above the middle on the temp gauge. I don't think the E39 has the link between the computer and thermostat like your 7 does; there are no wires that would indicate that and the E39 people have said nothing about it.

I have to make another trip and I'm pretty apprehensive about it, I hate getting stuck! I think I should replace the temp sender just for peace of mind alone though...

Rick

I have the M62 TU in the 2001 E-38 (V-8). It might make as much sense to change the thermostat as well.

One very important item...if there is a head gasket leak...it will gradually replace the liquid in the cooling system with exhaust gas. When there is insufficien liquid left to cool the engine, it will over heat. A compression check should diagnose this. One or two cylinders might be lower than expected. it is a pretty easy check.

Bob in Lake Havasu

Nowadays most temperature gauges work this way, if the car has any at all. I really hate that. As long as the needle sits outside the cold and the hot zone, there's nothing to worry about, it is very natural to have a fluctuating temperature, depending on load, vehicle speed, ambient temp,...

The electrically controlled thermostats on the other hand are clever. Keep temp high at lower loads, improving efficiency, taking down temp at higher loads, allowing to cool more.

Don't know about other car makes but Ford's new 3 cylinder engine has different circuits in the cooling system, depending on engine temperature one, two or all three circuits will get coolant circulation (stage 1: cyl head exhaust side only; stage2: entire cyl head; stage 3: entire cyl head + engine block). Makes the engine warm up faster and save bits of fuel.

Hi Rick, have you found yet what was causing this behaviour?

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Michiel 318iS
Hi Rick, have you found yet what was causing this behaviour?

Yes, Michiel, thanks for asking. It turned out to be a faulty electric fan in front of the condenser. Just like Peters Honda! Of course in the E39 it has it's own computer (with inputs from all over the place) that controlls the dam thing. So now it's just a matter of sitting down and figuring it out

There is a bright spot though, as soon as the gauge starts going up I switch on the defroster and the needle settles right back down. The car has a powerful heater/ac system the defroster throws everything on full.

Cheers, Rick

That's great news. A bad fan is much easier than a warped or cracked head. Had the exact same problem in my wife's PT Cruiser.

alan

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alanrw
That's great news. A bad fan is much easier than a warped or cracked head. Had the exact same problem in my wife's PT Cruiser.

alan

That's for sure Alan

Of course the fan assy is around 400 bucks and you have to pull half the front end off to get at it but hey, little by little we'll get there... Cheers, Rick