# Seeking 90 735i thermostat help



## crewdog843 (Mar 15, 2006)

Look at www.pelikanparts.com and seach for coolant flush. Gives you some insight into the entire process. Good luck.

Be careful with the places which do the flush for you....bring your own coolant which contains no nitrites or phosphates.

jake


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## kuailekafei (Mar 18, 2009)

I bought the flush kit, and have done a flush many times in the past. The only issue is the "closed" cooling system. Back in the past I always just ran a hose into the radiator and cycled it a few times. I am not sure how you do that with the BMW closed cooling system. And since it is so plugged up, I am afraid I won't be able to run it the 10 minutes that is suggested for a thorough flush. Everyone I have talked to has said I need some kind of vacuuming machine, but I am not sure what it is, or where to get it (aside from the ones I saw on that link you gave me, which were several thousand dollars). I have a few more calls I can make, and I hope to be able to figure out how to get this done soon. My secondary vehicle has no a/c, and it is getting hot here in Texas


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## markd2008 (Aug 7, 2008)

Hi,
I have an 88 735i and was having overheating and leaking issues a few months ago. I changed the thermostat with no improvement, I was having a heck of a time myself and was getting frustrated. I read somewhere on some website that you needed to bleed the system several times with the car on an incline facing up. They were right. I can't recall how many times I did it (maybe 8-10) but it worked. Each time I would get less and less air out and eventually I got none. Haven't overheated since. I also read about checking the coolant recovery hole which after each bleed to ensure the coolant is flowing into the tank, one article suggested that the small return hose does get plugged easily and just to blow it out. Mine wasn't plugged but sure enough the first few times I bled the system there was absolutely no flow before and some after. Previous to my overheating issues I lost heat as well. Now that the overheating issue has been resolved the heat sometimes does not blow warm (or starts warm and goes cold) turning the heat off and on again gets the heat (and defrost) blowing warm again. Its annoying but I can live with it.

This is a great forum and has been very helpfull. Glad your experiences have been more positive.
Mark


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## kuailekafei (Mar 18, 2009)

Well, my problem in the end was quite a bit more involved than just the return hose clog. I checked my fan clutch, and it was going out. When I dug in there to replace it I realized to my horror that the last "mechanic" to work on this car was a raging buffoon. I don't know if the previous owner paid someone to do the work, or did it himself, but regardless I found my problem: someone replaced the water pump, but over tightened the screws on the pully, causing two to snap in half. Both of the snapped bolts were on the same side of the pulley, therefore the water pump had an uneven distribution of pressure running across the pulley from the belts. The uneven torque totally busted the water pump bearing, and ruined the fan clutch. I had to go in there and replace it all, but the car has not overheated since, although my heater STILL doesn't work.

What I discovered to be a great help for the multitude times I had to bleed the cooling system: remove the bolt (14mm) on the thermostat housing, between those two sensors, and loosen the thermostat housing cover bleed valve while pouring in your antifreeze. Removing that bolt helps to back fill the engine block, and you'd be amazed at how much faster the air comes out of the system. I do this with the car flat on the ground, and it bleeds out right the first time (trust me, I had to bleed the system sooooo many times, first I replaced the t-stat, then cleaned out the return hose, the cleaned out the expansion tank, the replaced the fan clutch, then the water pump... each of those I did separately, thinking it was the source of my overheating... so I bled the system several times)

Hope that helps you


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