A) Test your cooling system pressure cap. It should not leak down and should release pressure above 17psi.

B) Install your new thermostat.

C) Test the fan clutch operation. You should hear it roaring when accelerating from a dead stop when the engine temp has climbed up around 105c.

D) If you suspect the fan clutch is not working turn the engine off and measure the radiator temp with your hand or some temp measuring device. The most crucial part is the core near the cooling fan. If its cool to the touch then the radiator is stopped up inside.

E) Make sure the fins are not stopped up with debris.

__________________
Scott Diener
89 300E
93 300E
92 Volvo 740 Wagon aka "Mutt mover"

Well I need to let everyone know what's happened so far (pardon the length). I'd like to close the thread at this point by saying everything is back to normal, but I don't think that's the case just yet.

I have been driving the 300E (keeping a close eye on temp)while waiting on my new thermostat to arrive. Careful driving has kept the temp down and everything has been ok, but my luck ran out last Wednesday evening.

I had stopped at an ATM for cash when suddenly there was a loud pop and an explosion of steam from under the hood. Temp had been a little high, but not bad because I had just stopped. I quickly shut the car off and pushed it off to the side to try and determine what had happened -- all the while praying for a busted hose. No such luck. I had a five inch split in the radiator below the upper outlet in the plastic side piece. Why didn't I order that radiator too!! Now I'm wondering if I've damaged the car.

Well, I got the car home and read everything in the forum on radiators. Even with the help of the forum's past radiator topics, I still couldn't decide what to get, Behr or Nissen. I was just plain sick with what had happened to the car anyway, so I put the decision off until Thursday.

Thursday I decided on the Nissen (taking Fastlane Phil's advice), and place my order (I've covered this under another post). I received and replaced the radiator and thermostat yesterday, flushed, and added 50/50 Prestone antifreeze. By the way, this stuff is called Prestone 5/150 Extended Life; and is silicate and phosphate fee; and meets DaimlerChrysler MS7170, MS9769 (whatever that means); and it's orange!!!

After a couple of short test drives around the block, I drove the car hard for an hour or so yesterday evening. While on the highway, temp stays around 87C. When stopped, temp stays low for a couple of minutes then slowly starts to creep up. When it gets just above the unmarked line between 80C and 120C on the gauge (what is the marking anyway? Does anyone know?), I hear the auxiliary fans kick on. The temp temp then slowly falls back down to close to the same as it is when running on the highway. Sounds normal? I think so from what I've heard here and from what my owner's manual states -- I really hate to see such wide swings though. Maybe I'm just gun shy now, and I really hadn't paid a lot of attention to how the cooling system acted until I had this overheating thing.

Anyway, there's more. I figured I still needed to test for proper operation of the aux fans, just for piece of mind. I popped the hood this morning to install an new pressure cap on the coolant reservoir (also for piece of mind), and for some reason decided to look at the fuses. When I removed the cover the first thing I noticed was that the card that tells what's what on the box cover was charred! The fuse in position "D" was the culprit. It looked like maybe the element had cracked but still made contact intermittently (causing heat). I dunno. I checked what I could read of the card (does anyone know if I can buy the card as it is ruined?) and saw that fuse "D" is the auxiliary fan!

So anyway, that's where I am now. I haven't replaced the fuse yet and I need to check some things I suppose. Any advice guys?

Ken Fuller
1990 300E (parked again)
145K Miles

Well I replaced the aux fuse and warmed the car up. The aux fans are acting differently now. With the ac on, both aux fans come on low speed with only a little rise above normal operating temp. I took it out on the highway and ran it a little. Brought it back home and watched it at idle some more. It's about 80F outside and now the needle on the temp gauge is not moving much above the 85C mark. Before, even after I replaced the radiator, coolant, and thermostat, the temp was going above the unmarked white line between 85 and 120 before the aux fans kicked in. Now, even after idling a while, the temp is staying pretty constant, with the aux fans cycling on and off early.

I guess the aux fuse really was intermittent -- to the point that the fans weren't able to kick on early in the temp rise. Anyway, I think it's now fixed. I hope this someone with similar problems.

Ken Fuller
1990 300E
145K miles

Ken,

Appears to be 'gold' star time! I would say you've fixed it. Everything you say appears as it should be from what I've experienced.

When it gets just above the unmarked line between 80C and 120C on the gauge (what is the marking anyway? That
line is 100C or 212F. If you car stays there, then it is perfectly 'safe'.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Ken,

To repair/refurbish/replace your fuse map go to

86 300E fuse box

JCE had posted a copy of his card from the 300E, although an '87, the cards should be close to the same.

Hope this helps.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

Thanks Mike and Jim. I've got my fingers crossed but everything has been fine all day. I think the major problem all along was the fuse. I'm an electronics guy by trade, but before I got this car I would have never suspected an intermitant fuse (this will be the second I've had). I suspect that the fuse was high resistance where it had broken. That is why the low speed never came on with the ac (not enough juice), but the high speed came on at high temp. I'll check out the link for my new fuse card.

Ken Fuller
1990 300E (on the road again)
145K miles