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Hi all,

1981 528i 5-speed.

Had the rad recored and just installed it.

Around town the temp gauge (assuming it's working) sits just under 1/4 all day long when warmed up. Cruise on the highway at 3000rpm steady it rises to just under 1/2, and high rpm (4500-5500rpm+) for even relatively short periods sends the needle up towards 1/2 or slightly above. It then drops fairly quickly to less than 1/4 when back to comfortable cruising speeds.

It was doing this before the rad was recored, but warmer at all levels.

Question - how much does the needle normally move in an e12? Where is it normally supposed to sit when warm? I'm think maybe thermostat stuck open issue, or possibly something else?

Any thoughts would be great.

Thanks

My '81 sits more or less centered most of the time at operating temps, unless of course air gets into the system. Yours seems to me to be reading low.

The question of course is whether the car is actually running too cold, or if your gauge isn't accurate.

If it was very cold out the day you were driving around then perhaps a stuck thermostat is the culprit, but I would think about whether there were some other symptoms, perhaps the engine was running rich?

Before cracking open the thermostat cover, I would probably start with the single-terminal sensor ( 62110788115 ) to see that it's clean and if it's in spec. Test it on your stove with an ohmmeter. At 140F you should read between 110 and 148 Ohms, at 194F between 46 and 56 Ohms and at boil (212F) between 35 and 42 Ohms.

A thermal imaging gun is also handy, but if you don't have a baseline measuring the upper radiator hose or thermostat cover for comparison, it won't be that helpful but at least you can get a ballpark gut feeling.

-Eric

thanks - I'll give it a shot!

Update - I just replaced said sensor as it was a $10 part.

It stays at around 1/4 most of the time incl. highway driving at 3k rpm constant. If I really rev it into the 4k-5k rpm range to fairly quickly moves up close to 1/2 and then falls back down to 1/4 when at idle or regular driving. Any other thoughts?

Any performance problems that you've noticed? It might be your gauge is bad, but if this were me I'd replace the thermostat next. Another cheap part and easier to do than opening the dash even though still a pain. Temp gauges don't fail that often, but it has been known to happen.

If you didn't do a full drain and flush of the coolant through the block plug when you replaced the rad, now would be the time to do that, especially if you notice a lot of crud on your thermostat.

-Eric

The fact that the engine temperature goes up when you're working it harder is not unusual. On my E3 the temperature will vary by 25°F depending on the outside temperature and the power level of the engine. It has been like this through 3 engines in 14 years.

Depending on how frequently (or infrequently) the coolant has been flushed through the engines lifetime, there may likely be buildup throughout the block. Below is a picture of one of my freeze plugs that shows severe buildup (it's kind of like hard chalk). Right behind the plug is the coolant-side of a cylinder, also coated in the buildup. Buildup can effectively act like an insulation layer between the coolant and the iron block. This insulation would result in hotter temps, as coolant efficiency is reduced.



Because our blocks are steel...like diesel engines, if you don't want to tear your engine apart and go to town with a dremel (like I'm doing), you can try diesel coolant cleaners like Fleetguard Restore Plus https://shopcummins.com/products/fleetg ... 8716050532

I have a 2004 Ford F350 dually with a diesel engine and I was surprised at how much crud flushed out when I performed a flush. I was referred to the Restore Plus by PowerStroke enthusiasts (despite it being a Cummins product) and I can personally vouch for it as well.

Mike

Thanks for all of the replies.

1. Driving wise feels and sounds great. I'm just not 100% sure what normal is supposed to be, and sitting at 1/4 seems low though I won't complain. I just want to make sure I'm not overheating my engine due to faulty readings.

2. I didn't do a full coolant flush, but it all looks pretty clean, and it was sort of doing this before the rad was replaced.

What about the fan clutch? I'll consider the thermostat and maybe the gauge.

Does the fan spin freely with engine off or is it seized? If seized it’s cooling when it doesn’t need to.

thanks - ill check.

Had a similar situation where is ran hotter at lower rpm’s. Turned out to be improper belt tension from previous work.

I forgot to add to my previous post that it's unlikely any buildup will be revealed in the expansion tank or even if the coolant was drained and inspected. This crud can only be removed physically or through chemical means (e.g. coolant flush).

Not implying that you have buildup, but wanted to state that it wouldn't be readily known either way.

Mike