I compiled the following list of cooling system temperatures to establish a baseline for monitoring temperature issues and I’ve posted it here in case it’s useful to anyone else. I’m assuming that my car is running at a “normal” temperature and I’m not accounting for ambient air temperature.


In my experience there is no change in readings when switching from OEM to the Mishimoto radiator but the only way to state that confidently would be to account for ambient temperature and engine load.

Thermostat housing temperature varied +/-10˚C over my tests and should not be considered accurate.

65˚C – Thermostat Housing +/-10˚C
80˚C – Top Radiator Hose
73˚C – Water Pump to Thermostat Housing Hose
75˚C – Bottom Radiator Hose

BMW e30 thermostat housing stat temperature
BMW e30 top radiator hose temperature
BMW e30 lower radiator hose temperature

October 16, 2014 mechanical, Uncategorized

After 20 years of being in the engine bay of an e30 any kind of plastic starts to… look like a cross between dried snot and old cheese. The coolant reservoir suffers the worst because without regular flushes the contents turn slimy and seep into the plastic.

Of course this in no way impedes functionality so replacement ranks low on the priority list. I’ve read that some (ABS) plastic can be bleached in peroxide and regain some of it’s original appearance but that can take weeks and produce marginal results. In most cases DIYers choose paint over replacement.

I’ve collected the following example photos of painted engine bay plastics for example:

My e30’s own coolant tank was especially pathetic. In addition to being cat-vomit brown it had picked up some overspray from the PO’s paint job and accumulated a thick layer of sludge in the bottom. The washer fluid tank suffered the same overspray but I painted that blue which I think really sets off well against the rest of the engine bay. I decided not to paint the coolant reservoir because I don’t have a space to paint in right now and it’s impossible to read the coolant level once painted.

During my engine swap I needed to fill out an order for some small parts and decided I’d add the tank to the order. I didn’t take any photos during the install but it was pretty straight forward and I think the results are nice.


1989 BMW e30 325i Clean Engine Bay and new Coolant Reservoir

e30 Coolant Reservoir

Coolant Reservoir Replacement

  1. Disconnect the Air Flow Meter and remove it along with the air box that holds the air filter.
  2. Put some cardboard and catch pan under the radiator and remove the lower drain plug.
  3. As coolant drains remove the cap from the overflow reservoir.
  4. Disconnect and remove the coolant level sensor by loosening the large black nut that connects it to the reservoir.
  5. Remove the coolant return hose from the bottom of the reservoir and immediately move it over the catch pan to drain.
  6. Cut off the radiator to overflow reservoir hose very close to the hose clamp, or cut the hose clamp off.
  7. Cut off reservoir overflow hose that runs to a hole in fender.
  8. Remove the old reservoir by pulling up to release it from the clip holding it to the frame.
  9. Put in the new tank, reconnect the hoses.
  10. Use either a very small worm-gear hose clamp or use the OEM “Oetiker Clamp” and end nippers (in lieu of the proper pliers) to connect the high-pressure radiator overflow to overflow reservoir hose.
  11. Refill the system with coolant and bleed it of any trapped air. This is well covered elsewhere in more or less detail.
  12. bmw e30 coolant reservoir

    Parts List

    Radiator Expansion Tank 17111712641
    Hose Clamp 32411712735
    Oetiker Clamps and Pliers on Amazon

May 26, 2013 cosmetic, mechanical

So much for “The Conclusion” of this tale. The story until now:

  • my mechanic replaced water pump, belts, hoses, coolant reservoir cap and radiator in May when I got the car
  • car was running cold in July and getting poor mileage, I replaced thermostat with a cheap one I had (may have been an 88C thermostat)
  • car started overheating so again I replaced thermostat this time with with a Wahler 80C, flushed rad and put in fresh coolant
  • ran fine for a couple days then more overheating. I replaced fan clutch, relay K1 and tested aux fan by jumpering switch

The last repairs were last weekend. On Thursday:

  • suddenly overheats on a short drive and scares the crap out of me with visions of a blown head gasket, temp gauge got over 3/4! – turned the car off immediately.
  • top rad hose is hot, bottom is cold
  • coolant level is high, must be due to expansion I figure
  • left the car on the street for a few hours and went back to get it after it cooled down
  • top rad hose is still warm, bottom rad hose is cold
  • squeeze the hoses, before and after thermostat housing and level in reservoir goes up and down
  • top up my oil (didn’t see any water in it but i’m not sure what I’m looking for in the dark)
  • drive it home

Get home, let it idle. Temperature goes a little over halfway but not to 3/4. Tapping the gauge sometimes made the temperature go back down. Fan is spinning great, chews up a cardboard tube nicely. Turn the car off.

  • squeeze all the hoses and they are super firm, system has pressure I guess
  • take the lid off the coolant reservoir and coolant spills out everywhere. that seems like it means something.
  • coolant level appears to be a little over the cold level mark but under the cap it’s much higher, must be cause by a trapped air bubble

My conclusion is a head gasket problem, hopefully nothing fatal to the engine. I’m going to have it towed to Bavarian Motorsport tomorrow since the problem is beyond my resources to repair as I don’t have a garage. Here’s what I would need to check if I was doing it on my own:

  • coolant leaking into the crankcase (milky emulsion in the oil)
  • “foaming” in the coolant system as exhaust gases are ejected into it
  • coolant leaking into a cylinder (white smoke from the exhaust)
  • coolant leaking from the head 
  • oil leaking into a cylinder
  • oil leaking from the head seam
  • a leak from a cylinder to the cooling system
  • a leak from a cylinder to an oil return passage
  • a leak between cylinders

It will be a few days before my mechanic will be able to get back to me, I’m sure. Fixing this could be expensive so I’m thinking about my options:

  1. have the engine repaired (welded). may not be possible. $unknown
  2. get a new m20 block / head / engine. $200-1500 + labor
  3. perform an engine swap $2000-10,000 + labor

Really, option 3 is the most attractive even though it will financially set back all my other plans for a while. It’d be great to get a 240-300 HP engine in my little car and put a silver lining on all these problems. But it would be really nice if it was something cheaper to fix.


August 25, 2012 mechanical