I've BMW 318i E90 2007 which is heating up after about 2-3 miles and since it has been heating so quick esp in down town and low speeds, I have not had a chance to take it to highways. Now, there are many things which have been done (potentially wrong) to this car.

  1. Mix brand coolant & water with no regard to ratio of water and coolant. Basically a ignorant mistake!.

  2. KSeal coolant was added as a percussion to stop any leaks if any.

  3. The Engine was re-built some time back by some local whose work I don't believe at all. And now I also suspect that the HG has blown as there is some knocking sound from day 1 after engine rebuilt.

  4. Sometime back (After the engine rebuilt), a pressure test on coolant was A OK. but there are definitely coolant leak marks on the ground.

I am now baffled with what to do and what not to. Here is what I've come up with in the order to get this fixed.

  1. Check radiator (Cooling system) for blockage and pressure test properly for long time.

  2. Coolant drain (with vacuum) and flush the system 2-3 times and pressure check again.

  3. Fill the system (Vacuum filling) with BMW coolant only with proper bleeding.

If these 3 steps don't work, change the Thermostat which might have gone bad after wrong coolant etc.

If change of Coolant thermostat does not work, then the Head Gasket.

I would highly appreciate if someone please help me and share their thoughts on my approach.

4 Answers 4


As you know the coolant is suspect, I'd begin with a full system drain, flush and refill, and check it all properly at the same time (rad, hoses, thermostat and pressure test). Thermostats can be tested by dangling them, and a thermometer, in a pan of water and gradually heating it to the appropriate temperature, then checking that the stat opens.

See if you can work out where the coolant marks on the ground are coming from. Coolant often leaves stain marks where it has run down the side of the engine that might give you clues. As well as the obvious areas, check the water pump, heater pipes and core plugs (round plugs inset into the side of the engine block)

If you suspect a HG failure, it'd also be worth doing a compression test on the cylinders and checking the oil for any visible signs of coolant (a creamy mayonnaise-like mixture forms when the two mix).

It is also worth checking that the cooling fan works properly and that the airflow through the radiator and fan isn't blocked by bits of leaves etc.


If you suspect the head gasket, you should immediately change the oil. If it doesn't look right (it will look "creamy" or "milky" if there is any coolant in it) you should immediately stop driving it and get the head gasket replaced. You may also be able to tell simply by checking the oil dipstick, but I'd recommend draining the oil and replacing it as a precaution. Unfortunately, I suspect this is the most likely explanation, since you say the car heats up quickly. A sticking thermostat won't cause that, although a blocked radiator or malfunctioning cooling fan might. If you get coolant in your oil, it can destroy your engine, which is why I recommend doing this step first. If the oil is OK then I think you're on track with the rest of your plan. I'd also recommend checking the fuse and relay for your cooling fan. These are quick and easy to check (and fix), so it would make sense to look at those before you spend much time and money on other things.

  • Coolant pump went faulty. so changed, refilled coolant and car is working just fine. Cost £240 for all.
    – NFS63
    Apr 25, 2018 at 3:58

Thank you Both.

Apparently the Kseal had clogged up thermostat. A simple thermostat change with radiator flush and new coolant fixed the problem.

There were no signs of HG damage but the mechanic said one thing very useful.


Mechanic suggested the below. - Change the thermostat & Coolant - Check the Water pump and radiator fan - HG

And he also suggested that this car may not be very reliable in the long run, in mechanic's code, get rid of it.

Thank You.


Looks like you have found the problem and solved it, but for the larger group who may face similar issue in the future this may help. Water pump malfunction is one of the most common problem in E90's, and the lack of engine temp (coolant temp) gauge on the dashboard cluster makes it difficult for any early warning signals, until you get the warning lights on. Also there are some easy trouble shooting steps you can follow to make sure water pump is the culprit.

  1. Temperature Gauge - You can use the additional options in the cluster window to activate Coolant Temperature gauge. There are lot of documentations on the youtube (how to check e90 engine temperature) on how to get it done. When you activate this you will be able to monitor real time coolant temperature. Different variants have different temperature range, but anything below 115 degrees centigrade is fine, you will also notice sudden drop in the temperature when the water pump is activated. This is one of the best visual means of monitor your engine temperature and to make sure water pump is working.
  2. 2E85 is the primary fault code for Electrical coolant pump malfunction/communication malfunction, however do not be surprised if no fault code is found.
    1. If you want to check if your water pump is working as expected, you can also perform the following test. Switch on the ignition, but do not start the engine, press the accelerator pedal for 10 seconds, if water pump is working fine, you will hear that it will start and stop several times (you will hear the sound under the hood).

Last but not the least, when I first got my E90, I felt that the hood was too hot, in fact as compared to my Hyundai Tuscon and Mazda 3, it was comparatively double the temperature, but later on I read through a lot of forum posts, and most of them felt the same, but there were no overheating problem.

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