The car is a 1980 BMW 320i, I've had it for a couple of months now and it has always ran a little to warm for my liking. A couple of weeks ago I did a complete coolant flush and much to my surprise everything came out really clean. the rad fins were full of crap and several were bent. I spent a good deal of time cleaning and straightening out the fins.
A couple of days after that the t-stat stuck shut on me. I was able to get it home buy turning the heater on full blast. I ordered a new t-stat but while I was waiting for it I drilled my old one and was able to drive it for a couple of weeks like that with it never getting much above half way on the gauge.
When the new one finally arrived I put it in and took a nice long test drive and all looked good. The next day on the way to work the temp shot all the way straight to the red mark, again with the heater on full blast I was able to get to work and home. I put my drilled one back in and sent the new one back for a replacement.
With the drilled one in and below 60mph or so it never gets above 1/2 but if I cruise much above that for any length of time and the temps start to creep up. As soon as I slow down or get of the highway the temps drop right back down. I figured it was because the area that coolant can flow through a fully opened t-stat is greater than the area I opened up by drilling it.
I got the replacement in yesterday and the temps shot straight up to the red again. I was able to keep it in between ¾ and the red mark with the heater on.
So I'm wondering if I got two bad t-stats or do I have some other issue?
If the water pump was bad I believe it would get hot even with the drilled one in. And it wouldn't drop temp when the heater is on because coolant flow would be the issue.
The bottom hose on the rad is cool to the touch so I believe the rad is doing it's job as well.
One thing I noticed is it’s not under any pressure. The upper hoses are very hot but I can remove the cap with no pressure even when it’s very near the red mark.
Any thoughts?
1: Cap is bad. The system needs to pressurize to work effectively.
2: The coolant was clean, but how did the passages look? Is it possible there are internal blockages or accretions? Flush as necessary.
3: Not that it is necessarily contributing to your issue, but did you drain the system from the block drain as well as the radiator? If not, do it. More than half the old coolant is still in there otherwise.
4: The water pump may not have failed completely, but they do go on these engines, especially if not maintained with phosphate-free coolant (you did use this, right?). Cheap and easy to change, and good insurance.
5: Proper bleeding of the system is key. That may have contributed to the overheat with the new thermostat.
6: M10 thermostats do not need holes drilled in them. If the system is functioning properly, they work fine as designed.
7: How clean are the radiator tubes internally? Just because the lower hose is cool doesn't mean it's working properly; there could be so little coolant getting through that when it finally gets to the outlet it's cool.
What you are describing is a coolant flow problem. You just need to systematically address the possible causes.
Thanks for the reply,
The passages looked clean from what I could see through the fill as well as the inlet and outlet nipples. Hell it looks like a brand new one compared to the mess that's in the cooling system in my 05 Grand Prix.
I believe from what I've read and your post that the pump is not moving enough water. I do not believe there are any blockages in the system at all. The car did sit for a very long time so maybe sitting in the old coolant for that long did some damage to the impeller? Any way it's a cheap enough part that I should just go ahead and change it.
Where did you buy the stats ? Adzones are crap, even though they have a lifetime guarantee.
Well the water pump fixed it.
OK edit that. It fixed it on my twenty minute test drive yesterday, on the commute today it shot up over 3/4. I guess it's the radiator even though it looks like brand new on the inside. I've heard having it boiled can help any experience with that? How much should that cost? Replacing the radiator is out of the budget right now. If I have to I'll put the drilled t-stat back in until I save up some money.
If it's a traditional radiator you can have it boiled out, but if it's aluminum and plastic, replacement is the only option.
Did you replace the cap? If not, you need to do that before doing anything else.
It's worth checking the ground on the instrument cluster; on 2002s, at least, a bad ground on the temp gauge will lead to erroneously high readings. The sensor connection should be checked for cleanliness as well.
Cap has been replaced and is holding pressure now. It's aluminium and plastic, the ground is interesting though. The fuel gauge has the twitches sometimes, and I did notice the coolant gauge twich once the other day. I wish I had another way to verify the temps.
You can verify if the radiator is plugged by checking that the heat is evenly distributed across the front or the back of the radiator with your hand.
Just place your hand near the 4 corners of the radiator and the middle, it should be pretty even side to side and warmer on top than it is on the bottom. If not, it is plugged.
Sometimes a reverse flush of the system can help reduce the amount of gunk built-up in the system.
Next time it gets that hot, try to pull over and verify that the radiator hoses aren't collapsing and that the radiator fan is running.
I'm wondering if you're fighting air bubbles in the cooling system? Make sure the thermostat opens properly (test it in a hot pot of water with a thermostat) and make sure it has a way of bleeding air past the thermostat (most can be drilled with a 1/8" or 3/16" hole) and see if that helps.
On the one you drilled out, you may need more restriction in the system, see if you can close the hole a little more to reduce the opening size?
Everything was flushed forward and reverse several times. This thing really was spotless on the inside, no scale, no debris on anything that I removed or inspected.
The fan is mechanical and the supplemental fan doesn't change the temp at all. I have it wired to the ac switch so I can turn it on at will. I bled it the same way I always have, I even went so far as to park it facing up a steep hill to help get the bubbles up to the neck.
Oh yeah, forgot about a possible lower hose collapsing under suction. How old is the lower radiator hose?
O.k. another day of useless attempts to help this.
I pulled the instrument cluster because my odometer gear broke and I need to count the teeth on the old one. While I had it apart I cleaned all the contacts for the gauges and tried to find a ground but I couldn't turn up anything. I don't know where it ground to but I couldn't find anything under the dash.
The thing that kills me is it doesn't act like it's hot. No smells, No hissing or bubbling and nothing under hood feels like it's that hot to the touch. The bottom hose is cooler than the top two and the radiator is hotter near the top and is slightly cooler down near the bottom just like I would expect it to be.
Two days this week it never got above half way on the gauge but the other three days it went straight up to red without even slowing down. This E36 M3 is driving me CRAZY!!!
BMW grounds are always light brown wires. Do you have a wiring diagram for the car so you can figure out where the cluster ground is located? The intermittent nature of the problem increasingly points to an electrical issue, but an infrared thermometer would confirm or deny it.
EvanR
Reader
10/16/11 5:51 p.m.
02Pilot wrote:
BMW grounds are always light brown wires. Do you have a wiring diagram for the car so you can figure out where the cluster ground is located? The intermittent nature of the problem increasingly points to an electrical issue, but an infrared thermometer would confirm or deny it.
This, or get a mechanical water temp gauge.
ford escort would be acceptable
