engine and drivetrain My 1600 runs too hot on the freeway, not bad in town - huh??

[bmw_jeff]

Hi all,

My 1600 has the original-to-67 4-blade fan which is not as good as the tropical fan obviously but I'm trying to keep it original. Anyway, it gets very hot, near red, on extended freeway drives, and actually cools off slightly once I exit the freeway.

I have had the radiator taken apart and cleaned/rodded out, and I have a new pump and new std. 180deg thermostat. Engine has been steam cleaned and is very clean. If I just drive around town it gets up to about 3/4, but on highway drives at 65mph or so it approaches just under the red mark but never exceeds it. I have 4.11 gears so it revs about 4k on the highway. The coolant is new 50/50 but I did not drain from the block bolt, just the bottom of the radiator and then more old stuff gushed out when I changed the water pump. Could gunk in the block be the problem?

Also, I think my needle reads a little higher than correct temp, as I need to work on the ground of the cluster, but still its alot higher on the highway speeds regardless. Thanks!

[bmw_jeff]

Oh, and no coolant leaks. Also re-built 118 head if that matters...

[DukeRimmer]

I think high on freeway, low in town is inadequate capacity. Small fan would be high in town. Three row radiator core? Pull freeze plugs and clean block?

[Guest Anonymous]

On andy's 1600 original cab with second over pistons and a 32/36 carb we run 1/2 around town and 3/4 at 65 mph. I would check the rad, thermistat and the fuel mix (rich or lean will make it run hotter). Also running the wrong oil (should be dyno 20/50) will cause excess friction and cause heat buildup. I would also check the temps with a lazer temp gun to make sure its not a guage issue.

Sam

[jpcapoc]

Curt Ingraham gave me some good advice. I had the same problem. Even though my radiator was recently cored also, it turned out that it just didn't have sufficient capacity any more. Since upgrading, I've had no problem at all, and it's been hot as blazes here in SoCal the past couple of weeks!

Curt is a heck of a good guy - very helpful!!!

[florida1600]

I would do the following, as my 1600 did the same thing even with a rodded out radiator:

1. Swap in the 5-blade tropical fan. You have the originality bit under control since there are only 4 or 5 florida 1600s in the US. It isn't any good if it overheats, compromising the engine.

2. Check your instrument cluster grounds and make a supplemental harness from the mounting nuts at the back of the temp and tank gauges to the sheet metal under the dash. You need to get a true picture of the "actual" operating temperature. Use a DVOM with a thermocouple to check the temps of the rad, hoses, and heater circuit to look for hot spots indicating air pockets or a lazy thermostat.

3. Drain the coolant. Remove the block drain bolt under the exhaust mani. You may need to punch through a layer of hard crud if no coolant drains out. Flush with fresh water. For the ultimate flush, pull the water pump, and stick a garden hose in the water pump port to back flush the block out the block drain. Refil with a 50/50 mix of BMW coolant and distilled water. Run the engine to operating temp wtih the heater on and ensure the wasser pump is opening correctly. Remove the radiator cap and jack up the front of the car. Work the throttle by hand with the car running in neutral and the rear wheels chocked until you see no bubbles in the radiator tank. This is to ensure the system is bled of air pockets.

4. If all else fails, consider the Curt Ingraham radiator or a good 3- core recore if it still runs hot at highway speeds. I think the 1600 generates more heat than people think since the engine is revving pretty high.

That prescription works for me in subtropical Pennsylvania.

[BigDog]

Here's an off the wall suggestion....

Check your timing lately? Too advanced and you'll run hot out there on the freeway! Good luck.

------------

BigDog

'76 2002

[KFunk]

I've had the same problem with mine, but now that I've but in a new brass 320i rad, water pump, and t-stat, its staying way cold, like 185 all the time, no matter what abuse I put it through. I haven't had the chance to do anymore long 75+ mph tests, but for the short distances I've went, its stayed right at 185. I've got the tropical fan too, because I am in a subtropical area. Not much highway here, though.

Also, for an easy quick fix, throw in a bottle of Redline water wetter. It does work, and will bring the temps down a good bit. I'm not gonna put it in my car right now, as its running so cold, it would be tough to get it up to operating temp with it in there.

[Slavs]

Hello Jeff,

I've had the same issues in the past. First of all ditch that small fan and mount the large tropical fan in place. I've had mixed experiences with rodding out radiators. New cores seem to do the trick. I currently run a recored to stock specks radiator. In the past I had a high capacity 2 row (not the 3 row) and it worked very well for 3 or 4 years. Eventually it got clogged because the high capacity cores have narower channels(more of them though) and they clogg easier. I live in Southern Cal where it gets pretty damn hot. My car runs 1/4 way up or just slightly above under most driving conditions. On the hottest of days it will get to about the 1/2 way mark or just slightly above, but rarely. You should also use the lowest temp thermostat. There are 3 diffrent temp thermostats. You will not change the originality of the car. Don't play around with high temps. Your head will take the punishment possibly cracking or warping. It doesn't take much. The 1600s run cool once everything is set up right.

Good luck and stay COOL

Slavs

[Slavs]

Hello Jeff,

I've had the same issues in the past. First of all ditch that small fan and mount the large tropical fan in place. I've had mixed experiences with rodding out radiators. New cores seem to do the trick. I currently run a recored to stock specks radiator. In the past I had a high capacity 2 row (not the 3 row) and it worked very well for 3 or 4 years. Eventually it got clogged because the high capacity cores have narower channels(more of them though) and they clogg easier. I live in Southern Cal where it gets pretty damn hot. My car runs 1/4 way up or just slightly above under most driving conditions. On the hottest of days it will get to about the 1/2 way mark or just slightly above, but rarely. You should also use the lowest temp thermostat. There are 3 diffrent temp thermostats. You will not change the originality of the car. Don't play around with high temps. Your head will take the punishment possibly cracking or warping. It doesn't take much. The 1600s run cool once everything is set up right.

Good luck and stay COOL

Slavs

[Brandon]

I had a similar problem on one of my past 02s and it turned out to be poor grounding in the instrument cluster. The temp gauge would always be around 3/4 to just under the red. I went through the entire cooling system and still had the problem. So when I went to upgrade the ground on the instrument cluster to fix the gas gauge from bouncing up and down as the turn signal blinked, I immediatly noticed the temp gauge reading at 1/4 to 1/2 under normal driving conditions.....who knew!

[Mike Self]

almost from the beginning of '02 production...my '69 came new from the factory with the small fan; I upgraded when the car was about two years old.

BTW, when I did a refurbishment on the car I went back to the small fan and a staggered two row core radiator and it works just fine around town and on the freeway--of course the engine is a little loose after 218k!

And the next time you remove the block drain bolt, replace it with a petcock--I found one at the hardware store that threads right into the block (take your old bolt with you). Makes draining the block a lot less messy.

Like the others, I suspect a dying radiator, rodded out or not. If you have your rad recored, have 'em add a proper drain petcock at the same time...

mike

[eastsidebimmer]

My 68 ’02 also does ½ way in town and ¾ (or more) on freeway (4K RPM)

I’ve flushed and filled, and tropicalized and cooler thermostated and I still have the problem. So, I’m going to wait for payday and get one of Curt’s radiators. If that doesn’t work, I’ll just drive till it blows up—I could use a rebuild anyway.

Ben

[bmw_jeff]

Thanks for all the tips guys! I think I will start with the cluster ground to be sure its not that, I know its not good because my other needles bounce around a bit. And add the tropical fan and lower temp thermostat.

[ingraham]

Spoiler: you need a better radiator, new or recored, not just rodded out.

Your temp gauge may be inaccurate, but the consistent 'low in town, high on the highway' reading says you need more cooling.

Change the fan if you want, but that's not the problem here. The fan provides air movement in slow or stopped traffic but contributes nothing on the highway.

For the mild weather of the SF Bay Area I recommend a 75 C or 80 C thermostat. It is a myth that a lower thermostat will overcome a cooling problem. A 71 C thermostat is useful in a track car, as it keeps the oil cooler. A 75 or 80 gets the engine temp up where it should be and gives good cabin heat in winter.

Next time you open the cooling system, refill and drain a couple of times with clear water. Use the block drain, too.

Thanks for the kind words. I've been keeping some of you waiting longer than usual. I apologize. It's hard to keep up at this time of year.