i have an 87 non-turbo 300D...

here's the situation, for the longest time i've had this super small leak in the cooling system... it loses around a liter of h20 every 3 days...with my current driving route with AC on...

anyway, I had my AC system recharged coz it was also losing freon every 2months... the shop did a good job with the recharge coz i never felt my AC blow that cold before, ever since i had the car, so i guess they filled the system with ENOUGH freon...

now the problem begins:
right after the ac charge, i noticed that my engine temp rose around 20 degrees above my NORMAL driving temp, which was 70 or so... then on the regular hill climb which i take everyday, i had to stop because the temp reached the RED zone...which caused a boilover, this happened 2 days in a row...

what gives? is it possible that by charging the AC with more than normal MY amount of FREON, the compressor became harder to turn? enough to cause the engine to overheat?

I'm thinking that if my AC became a lot colder, then the condenser upfront would have to be giving off more heat than what my engine was used to, in effect raising my NORMAL engine temps... in effect adding burden to my leaky cooling system, causing a boilover which normally doesn't happen...

opinions anyone? My temp sending unit crapped out today also btw, the connector popped out of the brass fitting... jeez... this happened after a sudden rise in temp, from 90 to RED in under 2 minutes... caused by boilover, lots and lots of water loss..

opinions anyone?

__________________

85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project

I think your analysis is correct.

However, the continued loss of coolant is not a good sign. Do you see where the leak is on the outside of the engine, or, is it possible that the engine is drinking the coolant?

If the engine is drinking it, you need to take some additional measures to confirm what you have. After it sits overnight, squeeze the upper radiator hose. See if it's "stiff". If so, then open the expansion tank cap and squeeze it again. If it's now soft, you've got head gasket and/or head issues that need to be addressed prior to any other problems.

The 603 is a bit sensitive to everything in the cooling system being close to spec. You'll get some mileage out of removing the radiator and thoroughly cleaning the fins with a proper condenser cleaner/compressed air/pressure wash.

But, if the underlying problem is head issues, all the other work is moot until they get resolved.

One additional point to note: If the engine is filled with a proper 50/50 mix of antifreeze and the pressure cap is working properly, it won't
boilover at 120°C. It appears that you have some issues on this front as well.

I would try replacing the cap first, it's possible that the slow coolant loss is also due to a weak cap. If the system isn't holding enough pressure, it could cause it to boil at less than 120. It's cheap, and you may get lucky.

thanks for the quick replies guys!

yup, there's a pinhole sized leak at the expansion tank, have to replace it soon coz its all brittled up... epoxied it for the time being... there are also telltale signs of small leaks at the plastic rad sides, evidenced by faint coolant streaks...

I don't use anti-freeze as i live in a tropical country... besides, i have a leak... water is cheaper. I do check the radiator hose once in a while in the mornings, soft and easy to squeeze... even the morning after the overheat... good sign?

a replaced the head gasket and had the head refurbished a while back, cause of a major overheat... had lots of posts back then, couldn't have made it without your help in fact. car ran fine since the head job... this just started right after the AC charge...

__________________

85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project

This is a major mistake.

"Anti-freeze" had specific characteristics to raise the boiling point of the fluid to safe levels. The fact that you have no anti-freeze allows the fluid to boil at a much lower temperature and you had the misfortune to witness this behavior.

Your engine has an aluminum head, as you know, and is quite sensitive to overheating. You've gone ahead and spent quite a bit of money to replace the head once. You sure don't want to do it again to save $20.00 in anti-freeze.

Furthermore, anti-freeze has specific corrosion inhibitors that are mandatory for the aluminum in the system. Without them leaves the aluminum in serious jeapordy.

A word to the wise.

yikes!

i thought i read somewhere that antifreeze corrodes aluminum, that's part of the reason why i don't use them, and put only distilled water in...

dang

__________________

85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project

Some anti-freeze is not compatible with the aluminum. You want to be using either the genuine M/B coolant or the Zerex G-05 if you can find it. That head is sensitive.........remember that.

You need to use the correct antifreeze for your system; MB type (from the dealer) or equivalent (Zerox G-05). You are not going to really going resolve this until you get rid of the leaks and put in the proper antifreeze mixture. Be very careful to not let the engine overheat with that 603 head.

Right. 'Antifreeze' is a colloquialism. Think of it as coolant. In your case the benefits of coolant include lubrication for the water pump, reduced surface tension vs plain water and corrosion resistance. If you run straight water for any length of time an orange scale (rust) will form in the coolant passages greatly reducing heat transfer to the coolant. In a tropical situation consider a 10-20% coolant solution and a bottle of Redline Water Wetter.

I hope there is a proper thermostat in your engine.

The question remains - what happened during the AC service that caused the sudden rise in temperature?

Sixto

i'll look for coolant first thing tomorow morning then.
thanks guys!

and yeah, i learned the hard way about the 603 head...

everything was a-ok before the AC recharge...

mr. sixto... i'm thinking that this was the first time my AC system was recharged correctly, i say correctly because this is the first time i felt that kind of COLD blowing through the vents. i may be wrong in assuming this, so i ask: IS it POSSIBLE to overcharge an AC system? What are the symptoms? and if it WERE overcharged, wouldn't it have blown up by now? I'm enjoying the COLDness of my AC, so i hope its the right amount of freon. I'm willing to go back to mediocre AC performance if it means saving my engine...
Though i do have to overhaul my cooling system as has been discussed.

replace expansion tank,
fix radiator leaks,
add coolant mix,
observe temp,
still overheats?
lessen FREON

see if this makes sense...
so overall, assuming AC charge is ok, my main problem is boilover?
... ACCEPTABLE and EXPECTED rise in temp because of AC working properly...
... BUT, my SUPPOSEDLY acceptable rise in temp causes a BOILOVER in my system because of ABSENCE of coolant AND cooling system PRESSURE leaks...
...thereby aggravating a rise in temp by DUMPING available coolant, thus causing another sudden rise in TEMP which causes ME to shut down the car...

could it be that simple?

__________________

85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project

Your symptom is excessive temperatures and a boilover. The change to proper anti-freeze will prevent the boilover. However, that is not the problem and replacement of the aforementioned items will be unlikely to cure the problem.

I'm assuming that the coolant did not get abnormally low prior to the system overheating. If it did get more than a quart low, then this can also be part of the problem.

My favorite task, as you might know, is to service the radiator, as this is the one place that always needs attention.

Two paths are necessary:

1) Internal: Boiling out the radiator can help with accumlated corrosion on the internal passages.

2) External: Using condenser cleaner and compressed air, together with water pressure from a pressure washer (carefully) will remove the accumulated debris on the exterior of the fins.

If the radiator is original and has a significant amount of internal corrosion, a replacement should be considered.

I think you're on the right track. If the AC system is working well, don't assume that is your problem. The folks who charged it should know what amount/pressure is required. It may just be aggravating your cooling system problems due to the extra load and heat. I would leave it alone until you address the cooling system issues.

I believe you have two obvious problems, the lack of antifreeze and the leaks. Both of these can cause your system to boil and overheat. You may find other issues later but you need to correct these first, then see what happens with the AC on and off.

thanks so much guys,

i'll get right on it tomorrow!

Mr. Carlton...
if i don't get results after the cooling system overhaul, what else would cause a diesel to overheat? aside from the usual cracked head, gasket issues? they're supposed to run hot anyway right? how hot is hot? here in the philippines its always hot, prior to the freon charge my car would rarely go beyond 80, it would stabilize at 70 or below, that was with mediocre AC, barely cooling during the day, worlds apart after the charge where it gets beastly cold during the day.

thanks again guys!

__________________

85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project

Do you have the correct thermostat installed? I believe your engine should have a 80C thermostat, so it should not be running at 70C or below. Around 80-90C is ideal. You do not want to run these engines without a thermostat.

Brian?

i honestly don't know if i still have that thermostat...

why wouldn't i want to run the car below 80C?
... dumb question: all MB gauges are in C right?...

__________________

85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project