Overheating 325?

[Dandydog]

I’ve got a persistent cooling-system problem in my ‘88 325ic: the temperature-gauge reading seems highly volatile (rising past mid-point more frequently than it ought to.)

The problem started about a year ago, with the engine temperature rising in summer stop-and-go traffic to the point where it blew hoses and those wonderful plastic radiator hose-clamp fittings. (I always got out of traffic and shut it down before the gauge got into the red, though.)


Partly in response to this problem I put in a low-temp thermostat, so that under normal operating conditions the temp-gauge needle points to the first hash-mark. Of course, this did nothing: low-speed operation in hot conditions still sends the needle unsettlingly close to the red zone.


I’ve tested the 91/99* auxiliary-fan sending-unit and rewired the connector without finding any problems: both fans come on with the appropriate cross-wiring (hence no blown fuses, either), and there’s continuity between each fuse and the corresponding connector pin.


However, when the problem recurred a few days ago, I did what I should have done some time ago (actually, I really thought I had): I looked through the grill and found that the auxiliary fan wasn’t running. (Checking under the hood, the engine didn’t seem to be over-heated: no heat shimmer, expanded hoses or the like. [This entirely subjective observation is probably optimistic and worthless.])


However, the seeming contradiction between the gauge reading and other indicators has got me questioning the temp sending unit and the gauge itself.


Has anybody got any ideas about possible causality or further testing? (Would it work to boil some water and immerse the tip of the brown sending unit? [Thinking further: and monitor the gauge as the water cools? That really oughta work, to my mind.])
Thanks, guys!

[Dandydog]

I forgot to mention that I’ve also replaced the head gasket and the rest of the stuff you’re supposed to, including the water pump.
Also that the car runs just great. (Aside from that, Mrs. Lincoln . . .)

[aaverhulst]

Have you checked the radiator?

[Mikealwa]

I'd buy a cheap Laser temp gun reader thing and see what the engine temp actually is. Maybe your gauges is off. Try hitting your dash ha, I have to do that every ride to get it off blue.

I bought a nice spal pull fan that seems to work well and I use an aftermarket fan controller with a temp sensor I put through the radiator. I can adjust the turn on temp on the fly with a knob. It's not elegant but works. I feel like you have an aux fan issue or the gauge is wacky or temp sensor.

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Also as mentioned above, maybe a restriction in your radiator could do that...not sure.

[82eye]

so the stock fan has been replaced by a pusher then ?
sounds like the temp sensor is out.

[Mikealwa]

so the stock fan has been replaced by a pusher then ?
sounds like the temp sensor is out.

What is your fan set up? Do you have an aux fan and the one that runs off the belt or just an electric aux? Should be a puller fan of it's behind the radiator. Pusher if in front of the rad obv.

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I only bring up the last comment, because my car came to me with a pusher installed behind the rad which isn't helpful. Good to check which way it's spinning never know.

[82eye]

What is your fan set up? Do you have an aux fan and the one that runs off the belt or just an electric aux? Should be a puller fan of it's behind the radiator. Pusher if in front of the rad obv.

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I only bring up the last comment, because my car came to me with a pusher installed behind the rad which isn't helpful. Good to check which way it's spinning never know.

i have the stock set up - puller fan on a belt behind the rad. loads of guys mod the cooling system, deleting the stock fan, and add electric pusher fans and temp sensors to run them.

[Mikealwa]

Haha I meant to dandydawg

[82eye]

Haha I meant to dandydawg

lol

[Mikealwa]

He's been scared off.

[richardodn]

Overheating in stop and go traffic is almost always the fan clutch. Perform the newspaper test. With the engine at operating temperature, try and stop the fan with a rolled up newspaper. If it slows down easily, you have a bad fan clutch.

Standard operation of the aux fan is
normally off
above 91C/196F, or with the AC on, fan comes on at normal (low) speed
above 99C/210F, fan kicks up to high speed.
Measurement for this is based on a reading from the switch(es) mounted on the radiator.

The typical failure mode on the gauge is due to a loose ground nut on the back of the instrument cluster. I'm not sure what this actually does to the gauge behavior. More likely is air trapped in the system causing superheated steam to hit the gauge sensor located on the thermostat housing. This might also explain the seeming contradiction between the gauge and the fan. See here for proper bleeding procedures https://www.bimmerforums.com/forum/s...6#post28749366

[Mataa]

I'd buy a cheap Laser temp gun reader thing and see what the engine temp actually is. Maybe your gauges is off. Try hitting your dash ha, I have to do that every ride to get it off blue.

I bought a nice spal pull fan that seems to work well and I use an aftermarket fan controller with a temp sensor I put through the radiator. I can adjust the turn on temp on the fly with a knob. It's not elegant but works. I feel like you have an aux fan issue or the gauge is wacky or temp sensor.

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Also as mentioned above, maybe a restriction in your radiator could do that...not sure.

What’s the meaning of the 200 on the center of the expansion cap tank? See photo:


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[323i E30]

That's 200 kPa, which is ~14.3 psi.
It'll lift to release pressure when surpassing that. It's for the coolant system what a fuse is to the electronics; a designed weakest point to prevent escalations in other areas.

[Mataa]

That's 200 kPa, which is ~14.3 psi.
It'll lift to release pressure when surpassing that. It's for the coolant system what a fuse is to the electronics; a designed weakest point to prevent escalations in other areas.

Ok
Is it safe for an old e46? Isn’t it too high? Just wondering.
I read somewhere about using a cap with lower pressure limit in order to relieve the cooling system from excessive pressure and thereby reducing risks of failure on radiator and pipes.


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[323i E30]

I’m not familiar with the E46
I’d just use the cap limit that bmw designed for it.

[82eye]

Ok
Is it safe for an old e46? Isn’t it too high? Just wondering.
I read somewhere about using a cap with lower pressure limit in order to relieve the cooling system from excessive pressure and thereby reducing risks of failure on radiator and pipes.


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if you find one toss it on and tell us how it goes. pretty sure they are matched to the year / engine / model series.
would be interested if they interchange. plus it's not my engine or head gasket trying it lol

[Mataa]

if you find one toss it on and tell us how it goes. pretty sure they are matched to the year / engine / model series.
would be interested if they interchange. plus it's not my engine or head gasket trying it lol

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[Dandydog]

I dug this thing out of the archives because I HATE incomplete threads.
Richardodn nailed it: it was the fan clutch all along, and the newspaper test he suggests is quick and definitive.
(Also: I wasn’t ‘scared off’ the discussion - it just got too cold up here to get the engine to overheat!)
Thanks, guys!

[Dandydog]

Re a previous thread:
An unsolicited update: 330K miles and running strong with the original bottom end. (I’ve done several head replacements)
(Okay: I’m tempting fate with this hubristic post, but I’m really proud of the old girl.)

[Mikealwa]

I'll join you in the jinx...I have 300k plus on mine, no replacements engine components. 🥲 Glad your temps are in control!