Symptoms of overheat diesel? 87 300D - PeachParts Mercedes-Benz Forum

a2t · #1 07-30-2008, 09:25 PM

My 87 300D is running hot. The pavement temps here in Atlanta on the connector are hitting 130F, and at times after spirited driving with AC on, then hitting a traffic jam the needle sometimes goes over 110C. Its even peaked at 120C briefly. I know this is very bad, and Im not sure really what causes this. It usually runs right at 90C, but if I get on it and run 90mph with AC blasting it seems the cooling system just cant keep up.

So all this heat may be causing the diesel fuel to become too hot - what is the upper limit ? Im running a frybrid system that heats the veg oil with coolant, and the wvo side of this works like a charm in this heat. But when I try to switch back over to diesel at these temps, it usually looses prime and stalls.

Ive double checked all the diesel lines for vac leaks, from lift pump to hard line, there arent any leaks. But Im wondering if the hot VO (what I would assume to be same as coolant temp, 110C) is actually heating the solenoid valve that dispenses the diesel fuel (since both fuels run to the solenoid valve). And this heat causes the diesel to bubble up and loose prime.

How can I make this thing run cooler? 3 seasons out of the year it runs at 90C or less, but when it gets extremely hot outside the engine just runs too hot. Perhaps a new rad is in order. Its the original at 275k miles. I took it out a year ago and flushed it, seemed to be OK (same flow rate coming out as in). But maybe some of the passages are blocked and coolant isnt flowing thru entire rad (dont know if thats even possible).

I wonder if the diesel fuel in the lines esp right at the solenoid valve that is stagnent during wvo use is just getting too heat soaked. How hot can you get diesel before you run into problems, and is loosing prime a common result of overheated diesel?

Dam its going to be 100 here for next week so this problem is getting worse. Once I do purge back to diesel (by revving motor excessively), it runs just fine on diesel. Its just the 1st 15 sec or so that it stumbles or dies when over 100C coolant temp unless Im at 3500 rpm.

vstech · #2 07-30-2008, 09:28 PM

I would first do a complete flush of the cooling system, then make SURE to follow the "citric acid" flush of the system. then put in the correct mixture of G-05 or MB coolant for the temps you are dealing with. for atlanta, I would put in 35-40% antifreeze and 65-60% DISTILLED water. your cooling system will thank you.

Oracle12345 · #3 07-30-2008, 09:28 PM

Hows your coolant?

Did you do a pressure test on your cooling system?

Have you tested your coolant?

you could add another fan that you toggle on with a switch?

Hatterasguy · #4 07-30-2008, 09:33 PM

How old is the radiator?

How does the fan clutch feel?

Is it dumping the AC above 110Cish?

My SDL never gets much above 90C and I run the AC a lot.

Brian Carlton · #5 07-30-2008, 09:36 PM

Quote:

Originally Posted by a2t

Perhaps a new rad is in order. Its the original at 275k miles.

Bingo.

A new radiator or a thorough (2 hour) cleaning of the external fins on the existing radiator after you remove it from the vehicle.

Hatterasguy · #6 07-30-2008, 09:37 PM

Ahh missed that, thats your problem.

As Brian said try cleaning it, and if that doesn't work get a new one. They don't last forever.

Also spray out your oil cooler when you do the radiator. You would not beleive the crap that I banged out of my old one when I replaced it, they are pretty low so they get a lot. Think 18 year old air filter!

ILUVMILS · #7 07-30-2008, 09:46 PM

Quote:

Originally Posted by a2t

How can I make this thing run cooler?

Before you spend any time or money on a cooling system flush, radiator, fan clutch, or anything else, make sure the auxiliary fan is working!

Brian Carlton · #8 07-30-2008, 09:49 PM

Quote:

Originally Posted by ILUVMILS

Before you spend any time or money on a cooling system flush, radiator, fan clutch, or anything else, make sure the auxiliary fan is working!

Probably not the issue if he's overheating after "spirited driving"..........which I take to mean high speed driving. That fan is of benefit in stop and go traffic when the clutch fan isn't pulling sufficient air.

a2t · #9 07-30-2008, 09:49 PM

Thanks, man you guys are on the ball here! That was 5 minute for all these replies.

I just flushed coolant system, its now running 60/40 water/Zerex. I also did have the rad out of car a year ago and flushed it thoroughly and cleaned it. I guess a laser gun would tell me if there were cold spots.

I have the mechanical fan, its all metal and is spinning with the engine on. How do I know if its spinning fast enough?

No, the AC doesnt cut out at 110C. Its only spent a couple sec at 120C but I didnt notice AC cutting out, I dont think it did. Next time it does this I'll pull over and see if the second fan speed is coming on. I know Ive heard it from time to time but I doubt its on all the time at these temps.

Is there a better rad to put in that will transfer more heat than the OEM unit?

And, would these temps cause me to loose diesel prime?

I did a pressure check on cooling sys a year ago. It held 15psi no problem (cold). Could it do that even with a cracked head or bad HG?

Hatterasguy · #10 07-30-2008, 09:53 PM

Custom really, their is no aftermarket radiators. But a new Behr will be more than enough. MB designed these cars to run in the desert! Stock is enough.

vstech · #11 07-30-2008, 09:59 PM

the way I read it, his "spirited driving" holds the temp fine, it's just when he slows down to a crawl after such speeds that the temp climbs!
that sounds like a fan clutch to me. the original is VERY PRICEY, but the updated one from the 606 is pretty affordable.
to test the fan, go "spirited driving" and then park and turn OFF THE CAR!!! immediately pop the hood and see if you can freely spin the fan, or if it is very firm.
it should be firm and not able to spin by hand more than 1/2 turn or so. if it freewheels, you have a problem.

a2t · #12 07-30-2008, 10:06 PM

Will do, I'll test that fan tomorrow and report back.

One more clue, perhaps...

The #3 injector is wet on the body where it screws into head. the little 1/8 was cracked so I replaced it but injector is still getting wet. I wonder if this could be a vac leak somehow causing it to stumble or stall when hot. What is this heat shield Im hearing about in other thread? A washer of sorts that goes under injector? Maybe that needs to be addressed too, probably not related to this problem.

And yes, as long as Im moving the temp stays pretty constant below 110C. If Im really gunning it it will get to 110C but soon as I slow back down to 70 or so it cools off. Just when I hit a stop that I loose airflow and things get hot. Maybe Im driving this car too hard...

So if it is the fan, I can just repl with a 606 unit with plastic fan and it drops right in? If my fan is spinning, that doesnt mean its working? Why not just have it directly connected to motor so it spins with rpm, or would that just overspin fan and make engine run too cold.

Come on October!!

Johnhef · #13 07-30-2008, 10:22 PM

You could do it but its designed to slip when not needed to have less strain on the engine i.e. less fuel use, etc.

How is your thermostat? My 2yo MB one stuck shut on me and cooked my car last year.