How many diesel owners have had problems with overheating????? - Page 2 - PeachParts Mercedes-Benz Forum

gsxr · #16 09-11-2002, 03:06 PM

RLN,

Good lord, man! Don't ever let your car get up to 120C!!! These engines have a problem with cracking the heads when overheated. Just pray you haven't damaged the engine yet. Search the archives on this forum for more information (I've had to put a new head on one car already!)

First, to correct an error by PEH - don't ever operate a Mercedes engine with the thermostat removed. The t-stat is the bypass type and has two functions. It is explained in the OM602/603 engine manual complete with pretty pictures, it's worth reading. Basically the t-stat, when hot and open, forces coolant to the radiator to be cooled. With no t-stat present, coolant is NOT forced to the radiator! It is actually possible to overheat the engine with no T-stat installed! This ain't a small block Chevy, folks... VERY different cooling system design. Look, I'm not making this up, I'll post the PDF of the service manual section on my website if you don't believe me.

Now, about your problem. I have two of these cars and my sister has another. All three exhibted overheating problems to various degrees (yuk yuk) when first purchased. I have since fixed all of them. From what you describe, it is VERY VERY likely your radiator is plugged! Your fan clutch *may* be fine. A new Behr radiator is $325 from ***************. A new Nissens is $250, however the Nissens does not have metal reinforced necks and also requires cutting of the left plastic tank to make it fit. The third option is to send yours to Reseda Radiator, they will re-core yours for $125 plus S&H both ways (roughly $175 total). You decide what is best. But I wouldn't drive the car hardly at all until this is fixed! A new head will cost you about $4000 installed ($2500 parts, $1500 labor).

Other tidbits:

1- Now would be a good time to replace all 5 rubber coolant hoses that are more than 5 or 10 years old - don't forget the one hiding under the turbo area!

2- Replace the T-stat if you haven't done so already (cheap insurance)

3- Check the fan clutch for proper operation, but if the car runs 85C on the freeway, it could be fine. If it still has the metal fan blade it may be original, which is not good.

4- The aux fan temp switch on top of the engine (3-prong switch near upper rad hose) has failed on 2 of our 3 cars (no longer turns fan on at 105C). Again, it's cheap insurance ($20) to just replace it!

5- Use a full bottle of RedLine Water Wetter, and only MB antifreeze. Use less than 50% a/f, especially if you live in a warm climate (I run about 20/80).

6- The temp gauge sender tends to get out of calibration after 10+ years. They are only $10 and are IMO cheap insurance. They're a minor pain to R&R, located on the cylinder head between glow plugs 1 & 2 (or is that 2 & 3?)

All three of our cars now have new (well, replaced in the last 2-3 years) radiators, fan clutches, thermostats, hoses, and temp senders. All refuse to go above 105C under any conditions and usually stay under 95C, unless idling in traffic on a 110F day for extended periods. Yours should be the same way.

Best regards,

fredjj · #17 09-11-2002, 03:41 PM

Had an overheating problem while running w/AC at 75-80 mph in the summer. Replaced the probably original 240D radiator with one off a 300D last summer. Now always at 180F, even in winter.

gsxr · #18 09-11-2002, 04:57 PM

CHAPP,

Reseda Radiator specializes in rebuilding radiators with plastic tanks. It costs more (obviously) than the $50 for a local shop to do a metal-tanked unit, but $125 is still way cheaper than a new unit - IF you can afford to have the car inoperative for a week or two.

And you would be surprised how fast a new radiator can plug internally and/or fail. My first 1987 300D, bought in 1997, ran way too hot. I assumed the radiator could not be the problem because it was only 4 years old, replaced in 1994 with a new BEHR at the dealer. Well guess what, after replacing *everything* else and tearing my hair out, I finally tried the radiator out of desparation. Guess what, temps instantly dropped and it has run wonderfully cool ever since. There was no other sign the rad was bad, either - no cold spots, no flow problem visible with a garden hose stuck in one end, etc. It allowed flow but it didn't transfer the heat from the liquid to the fins!

I see this complaint (hot running) all the time on the late 80's OM60x engines, and it's quite common for it to be the radiator instead of the t-stat or other "simple" things. I think part of the problem is the little "turbulator" fins (or whatever they're called) that Mercedes used inside some of these radiators. I think they collect debris and reduce efficiency, but I'm not sure... just speculation on my part. The fan clutch really can cause problems too, even on the highway. There was a recent thread here about that too. People think the ram air effect is adequate at freeway speeds, but as others have proved it sure isn't! The fan and clutch MUST be operating properly in order to cool the car both at idle speeds AND at freeway speeds. BT, DT. Trust me! :p

Regards,

Piotr · #19 09-11-2002, 05:20 PM

To all guys suggesting the radiator prob. with plugged radiator, the overheating would get worse under load (read: higher speed). It DOES NOT!!! to you fan clutch fans (pun intended)- it's a possibility, but clutch can be easily tested- should shorten your fan switch pins. if the main fan works, then it's the switch, if it doesn't , it's the clutch. Prove me wrong!:p

abedford · #20 09-11-2002, 05:40 PM

I had the same creeping temperature problem this year.
After replacing various parts of the cooling system, the biggest change came from bleeding the air from the coolant at the heater. There is a small (8mm) hose that is higher than all parts of the cooling system (including the expansion tank and cap)on my car. It's located between the cowling and the firewall. It's attached to a small hose barb coming out of the cowl. I connected the end of the hose to another hose and submerged the end in a bottle of coolant. I then ran the car and watched as it sucked up about a quart of coolant before coming out of the hose barb on the cowl. I reconnected the hose quickly, so as not to allow any air back in.
The temperature is now perfect all the time. And operating temperature always makes a big difference in the way a diesel performs.

gsxr · #21 09-11-2002, 05:40 PM

Good point - but it depends quite a bit on the ambient air temps. On my car with the bad radiator, it was FINE in the winter - never got over 95C. But on a hot summer day with the AC on, it would shoot up to 115C at idle, and run 100-105C on the freeway. It is still possible it's the radiator, and that at freeway speeds the fan is pulling enough air to keep it cool. Alternatively it's possible the rad is OK and the main fan isn't pulling enough air at idle (bad clutch). Like I said, test the clutch first. I still am 99.44% positive the problem is one or the other (or both combined). I'm all ears waiting to see what the cure is, if I'm wrong I'll eat my hat with a knife & fork!

stephenson · #22 09-11-2002, 09:00 PM

Back to original poster ...

If your car is overheating at highway speeds it can be:

- lack of pressure in coolant system
- lack of coolant
- bad tstat
- bad coolant pump
- bad radiator
- blockage in lines, passages, etc
- bad head gasket, cracked head, etc

Start:
1. Check cap and neck area of overflow tank for cracks
2. Make sure ya got coolant (duh)
3. Replace thermostat (folks have gotten two bad in a row)
4. Check coolant pump for leaks ... it is possible to have a bad impeller, but it is somewhat unlikely
5. Check for blockage in lines by doing feel tests (do search and get rundown on which lines to feel and when)
6. If all above fails, its gotta be the radiator - check for large mass of bent fins and then for junk in it and then for blockage

Personal opinions:
1. Most likely causes are: lack of pressure in system, bad tstat, too much coolant in water (shoot for 40/60 or so, radiator issue (last)
2. Have seen nothing to indicate water wetter does anything; if it does it is so far out on the margin as to be irrelevant

Good luck ... these are maddening things, but keep at it and carefully evaluate everything.

gsxr · #23 09-11-2002, 09:57 PM

Actually, George, the original poster stated it runs OK on the highway (~90C) but shoots to the redline in traffic. Could be as simple as bad rad cap or low coolant but not likely. He indicated he's already done some (unspecified) work on it, I'm guessing a flush & refill at least, and verified proper coolant level.

I agree with the rest of your post except for one small item. A bad coolant pump almost NEVER causes overheating. In order for it to do that, the impeller would have to separate from the shaft (practically impossible). Usually when the pump fails, it leaks. Now if the leak caused a massive coolant loss, and the low coolant idiot light on the dash isn't working, then it could be an indirect cause...

But 99% of the time it's one of the other items you mentioned.

I so heavily steer toward the radiator or fan clutch because 1- I assume the poster has already tried the simple stuff, and 2- as mentioned in my other posts I have seen this on my personal 3 cars (of the same make, year, model, and engine as the original posters') as well as several OTHER people's 1987 300D's. If those 2 items have never been replaced, it's almost guaranteed they are shot. And if they're more than 5-7 years old, same thing. BT, DT!

BTW, you might want to read Red Line's documentation on Water Wetter for details on exactly what it does and how it works. Neat stuff, and not terribly expensive.

Oh yeah, Mercedes made a change to the plastic coolant reservoir on these cars. The new one has a silica gel pack inside to help combat corrosion due to the aluminum head & radiator. If you haven't replaced it yet, it sure wouldn't hurt. They are about $35 from online sources. Both of my original ones were pretty cracked on the back side, where you couldn't see it. I was glad I changed mine. And the new ones look much prettier too! Nice and clear, instead of yellow & brown. Now I can see the coolant level without removing the cap, even with the yellow MB coolant! Sweet! :p

Piotr · #24 09-11-2002, 10:12 PM

OK, gsxr- you've got yourself a bet!! I still say its the fan switch!! all others would result in a temp creeping at speed (your post notwithstanding!). With the bad pump a little revving up at a standstill would cause the temp to drop. Bet ya it will not in that car! bad fan clutch is a possibility, but a low one (of course my only experience is 190d, with an electromagnetic clutch). I hope Kevin will fix it and tell us what's up

By the way, can you tell I LOVE controversy and discissions..

CHAPP · #25 09-11-2002, 11:54 PM

Well my radiator was 6-7 years old and my friend with a shop got me one wholesale for $135, so I didn't look any further. When I ran heavy equipment this was a common problem, if we did not use (CAT) or any coolant conditioner, new raditors would only last a year or two...they would just stop cooling. Cat claims that this is natural with diesel engines if conditioner is not used. This is a big deal when you run a machine full throttle 8 hours at a time, 5-6 days a week. But as stated in previous posts...it can be almost anything.

stephenson · #26 09-12-2002, 10:39 AM

gsxr,

Yeah ... in my haste, I got the overheat issue backwards ... sorry.

Agree, that if fine at highway speeds (air flow is sufficient to cool normally) that it is likely viscous clutch or electric fan (sensor, switch, relay, wires, fan motor). I am not even sure the radiator would be where I would look if it was OK on highway ... would seem simply to be an airflow problem.

My comment on water wetter comes from watching how some products get endorsement from independent sources ... I have yet to see any data, other than from the manufacturer ... to substantiate their claims ... and, I am particularly interested to know if the very minor differences some folks claim are simply caused by them decreasing the coolant to water ratio (which would increase cooling capacity at a relative decrease in freeze protection and boilover protection).

gsxr · #27 09-12-2002, 11:05 AM

I see where you're coming from about the Water Wetter. But to me, the fact that Red Line is a reputable brand of highly regarded performance and racing lubricants gives them a lot of credibility. If Water Wetter were made & sold by, say, Slick 50 then I'd probably ignore their claims entirely. But Red Line makes good stuff, hence my tendency to believe their claims (which are pretty reasonable, and not outlandish).

I'll keep mute on the cooling problem for now, until the original poster (who never gave his name, so I don't know how else to refer to him) replies with some new information. If he's still reading the thread, that is.