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Discussion Starter · #1 ·
Hi All

I have a BMW 525i Year 2002, it doesn't have thermostat, there are no water leaks, the pump is working fine, the auxiliary pump is working fine too, when I go in the road sometimes it get hot suddenly and in other times it runs at normal temperature, what do you think it could be? I'd appreciate your help. Thanks in advance.
 

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An indie had told me that if there is any air in the system this could cause intermittent overheating. I myself have a similar problem at the moment. My dad was driving my car about a week ago and he had overheating problems but no leakage. I'm having it check out in about a week. I'll try and remember to post here with the feedback.
 

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How do you know that it doesnt have a t-stat? It is enclosed inside the plastic housing. The car would never get to normal operating temp without the t-stat. Agreed with others about air in the cooling system. Search the forum for proper way to bleed and refill.
 

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How do you know that it doesnt have a t-stat? It is enclosed inside the plastic housing. The car would never get to normal operating temp without the t-stat. Agreed with others about air in the cooling system. Search the forum for proper way to bleed and refill.
I do believe that when the thermostat opens, it blocks a radiator bypass port. Without the thermostat, there is no way to ensure that coolant actually flows to the radiator, since the bypass port would always be open.
 

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Actually, people in the tropic (Mexico, Caribbean countries) sometimes remove the tstat thinking that since they live in the Tropic, there is no need for it.
Wrong, a tstat is necessary even in the Tropic!

(The O.P. is from Mexico).
 

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Wrong, a tstat is necessary even in the Tropic!

(The O.P. is from Mexico).
Yes, I noticed he was from Mexico, but didn't know that they routinely remove their thermostats in the tropics.

I just double checked the I6 thermostat configuration and it does, in fact, have a bypass port that closes when the thermostat opens. That large disc on the thermostat moves to obstruct the port. If there is no thermostat installed, then there is no guarantee that any water will flow through the radiator. So water to air heat exchange will be random unless there is a thermostat installed. Without a thermostat, water can and will simply flow through the water pump and back through the engine, never making it through the radiator.
 

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Discussion Starter · #10 ·
Ok Guys

I started the engine for large periods without run and check the floor looking for a leaking and nothing found.

Because of my desperate I took the car to a friend's garage, so he told me there is no thermostat, anyway I'll buy it and install, this will be my first step, I'll let you know how it is going.
 

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I have a BMW 525i Year 2002, it doesn't have thermostat
Like all the others said, I have a 2002 USA-spec 525i, and it definitely has a thermostat.

they routinely remove their thermostats in the tropics.
I thought the 2002 525i thermostat was a monolithic unit - at least mine is - so I would think removing just the thermostat from the housing would have to be done on purpose and with dedicated intent.

he told me there is no thermostat, anyway I'll buy it and install, this will be my first step
I'd look for it first. It's probably there. I don't know how your friend can tell that it's not there without removing it anyway. If he didn't remove it, how would he know (since from the outside, you wouldn't be able to tell)?

 

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Make SURE you purged it correctly. Here's my story from this week:

I posted my used fan clutch on Craigslist - the clutch is fine, I just changed it as part of my cooling system overhaul. The person that responded to my ad wanted to know how he could tell if his fan clutch was actually bad. We talked for a while, and it seems that his '95 535i overheated, and since then it continues to do so, despite his refilling and purging the coolant. I went over to take a look at the car, and saw no obvious problems. I had him start the car with the expansion tank cap off and all looked normal. I opened the bleeder, and the coolant level stayed the same. We watched the gauge as it climbed, and as soon as the thermostat opened, the expansion tank went dry. I added a full 2 quarts of water to the car before some coolant spilled from the bleeder.

Since then, he has not been able to get the car to overheat.

When he refilled the coolant, he did open the bleeder, but did not have the engine running, nor did he continue to bleed the system until the engine reached operating temperature. He also did the refill in his garage with the car level. I did the refill in his driveway, with the front of the car slightly higher than the back.

Whether this is the 'authorized' procedure or not, it worked for us. YMMV.
 

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Discussion Starter · #20 ·
I checked the water-pump and it looks fine, the fan clutch is working fine as well, the temp sensor is new also. I think it could be the auxiliary water pump because when I was purging the system the water was going away the hose without much pressure, do you think it could be the problem? as far as I know the auxiliary water pump works only when the car is hot.
 
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