124 603 Strange Overheating issue
 

Hi,

I'm new to the forum here.

I have been having an engine running hot problem with my 87 300TDT for a while now but it has recently gotten worse.

The car runs great, however, under load, going uphill especially, the temperature will climb, albeit not all the time. This is especially true for the long highway hills. The temp normally runs at around 85c. Going up a hill it will climb to 110. In extreme circumstances, 120. I try not to let it get to that though.

I have replaced all the hoses, thermostats (twice) radiator, fan clutch, fan blade, pretty much the whole system except the water pump, which is not leaking, and the electric fan, which works.

The tricky thing is the previous owner put in a vegetable oil system and messed with the cooling hoses to heat vegetable oil. It is a lovecraft Biofuels system. I had it removed last week, and now a new problem has come about.

The car now runs hot on the freeway, and especially under load, but it will not run hot in local driving, no matter how many hills I do. Very small incline and the temp shoots straight up.

I don't think it is the gauge because it gets hot only under load, and now with light load under freeway driving.


Can someone please help me with a suggestion?

Which thermostat did you put in? did you verify it opens at 80C?

Does this kind of behavior present itself in the 603 when the headgasket has gone south?

verify that the fan clutch actually engages the fan when you hit the 90 to 100 mark, it should pull a colossal amount of air when engaged. Also check that the radiator evenly warms up, it might just be air trapped in the system somewhere when you rearranged the pipes.

Yup.

The behavior observed by the OP is somewhat typical of the 603 under load, however, the climb past 105C. is definitely extreme.

As mentioned, the thermostatic fan clutch in front of the radiator is a key component in keeping this engine below the red zone. Once the engine hits 100C., the fan should be fully engaged and making quite a bit of racket in moving a significant amount of air.

If the fan clutch checks out, the real question is the age and condition of the radiator. If the radiator is original, it most certainly is a contributor to this behavior.

The suggestion that the head gasket is compromised without any supporting evidence other than higher than desired temperatures under load is simply a WAG that is worth nothing.

Make sure that if you bought concentrated coolant, you remembered to cut it with water. An electrolyte tester is cheap and will tell you about your concentration.

Fan shroud still there?

Pump timing where it's supposed to be?

A hydrocarbon test will quickly rule out the possibility of a head or head gasket.

He lists the radiator as having been replaced; although he doesn't say how long ago. So unless the condenser is completely plugged with 25 years of crud the mystery deepens.

Is the radiator hose still filled with pressure after sitting overnight?

Factory replacement from the dealer, did not verify.

I'm hoping not. I ordered a engine oil analysis so I should know soon enough.

[QUOTE=TheDon;2946698]Which thermostat did you put in? did you verify it opens at 80C?[/QUOTE

Factory replacement from the dealer. I did not verify the 80C.

Fan shroud is there. I should check out the pump timing, wasn't aware that there was such a thing. Thanks.

The radiator is a factory replacement by behr and it is less than 6 months old. The hoses are not still pressurized after sitting overnight.

So I got my handy Fluke infrared temperature gun. I ran the car on the freeway again and replicated the problem. When it was hot, about 110. I pulled the car over and took some temperature readings. Auxilary fan was not running. Here are the readings in Celcius.

Upper coolant hose: 72.222
Lower coolant hose: 58.8
Radiator reservoir cap: 62
Cylinder 1 head: 82.2
Cylinder 3 head: 94.4
On radiator: 84.4

So, any ideas? Is my temp gauge off? It is important to mention I saw some relief pressure coming from the overflow cap, indicating it is actually that hot.

Will investigate some more, and get the oil analysis before I start dumping money in it. I know this can be characteristic of the 603, but is a bit extreme.

Squeeze the upper radiator hose after the car has cooled down over night. It should not be holding pressure. Have you cleaned the outside of the condenser? The air has to flow through it to reach the radiator.

The cap does not release due to heat, it releases due to pressure.
The pressure could be due to heat.
The pressure could be a failed head gasket.

check the resistance of the temp sender when the engine is at 100, and the surrounding area besides the sensor actually reads 100C on the infrared, There is a spec of it on this forum and they can go out of sync, and our temp gauges are nearly "actual" temp gauges unlike new japanese cars whose temp gauge serves purpose of an idiot light.

Heating to nearly-dangerous temperatures only during long uphill grades was one of the only two behaviors my 300SDL exhibited when the head was cracked.

The other was that the system held pressure overnight. You'd drive for a while, get everything hot and pressurized, park in the evening, and the next morning when it should have been stone cold, the hoses were still hard and when you opened the pressure cap, you got a very noticeable hiss as the pressure escaped.

That's an easy test to do. If it happens, head gasket and/or head is a more likely suspect.

Just making sure you know he means IP timing.

Tripple check that Fan Clutch
 

My 86 603 really needs a good fan clutch to stay cool when summer comes. No problem below 90*F. But above that the 603 realy needs that fan yanking lots of air through the radiator or it will get in the +100C zone. By the way....needs it a highway speeds too cause there is too much front end (body & mechanical) deflection to pass the required air flow at high ambient temps.

They (fan clutch) seem to loose thier "grip" after a while and not rotate the fan as fast as needed, even after 5-10k post installation for aftermarket jobs.

Fooled before so now when summer comes I replace it, or as last week added silicone. Also wash the AC condensor & radiator fins.

Today (post fan clutch service & "fin" cleaning) I'm in the Phoenix area with ambient temps up in the 111 to 115 range. Had the AC cranked to max all day, temp guage never made it up over 95*C. Mixed driving with stop & go to 75mph.

Like others say your temps may be due to other componets / head condition but I for one don't trust those fan clutchs farther than I can throw them. Very sneaky b*stards

You're not alone. AFAIK Steve/swogee is on year 8 of the same problem - http://www.peachparts.com/shopforum/diesel-discussion/102579-1987-300tdt-overheats-long-hills.html

Sixto
87 300D^2

Do you have a 1.4 bar (140 marking) cap on the reservoir? How would you see it overflow? A hose goes from the neck to a bottle in the fender.

The aux fan trigger switch on the 124.133 is rated for 105*C. It's the 3-pin switch atop the turret to which the upper radiator hose attaches. I forget which pin pair to jump to test the aux fan. It won't hurt to jump pin pairs to test the fan. One pair triggers the fan (105*C), another pair cuts the compressor (IIRC 127*C in a 124.133, say what???), the third pair does nothing. An 86-87 switch has a lower AC cutout (120*C?), an early 300E switch has a lower still AC cutout (115*C) and a 190D (red top) switch is the lowest I've found rated at something like 95/110*C. Yes, the 190D switch has a lower aux fan trigger which helps cabin cooling on hot days. And when the temp gauge reads 110*C, I won't need AC since I'm not going to drive the car further.

Sixto
87 300D^2

The highest temperature with the infrared gun is 94C. The dash gauge is reading 110C.

Clearly, either the sending unit (most likely) or the gauge is in error by a serious amount.

Sure, it's "that hot" being 94C. But, it's nowhere near 110C.

You don't have any head gasket issues.

For the cost it would certainly be worth trying a new temperature sender.

Is it possible for a temperature sender to work correctly up to a certain temperature 80°C for example and then send an inaccurate signal as the temperature of the engine rises?

Hooverfull can you repeat the scans with the IR gun when the gauge in the car reads 80-85°C or whatever the gauge reads during normal conditions?

Still trying to troubleshoot the issue
 

OK, sorry for being out of touch for so long, but this, by no means is the problem solved.

To recap.

The car overheats on hills. Used to be it got hot on long freeway hills, but now it would just overheat just driving uphill on any load.

I have replaced:

Thermostat
Radiator Cap
Radiator
Coolant 50/50 mix
Fan Clutch
Fan
Shrouding
Water pump

I have not replaced the temp sender, but it seems to work since it seems to know when the car is going uphill. I do think the needle on the guage is a little jumpy. Also, the car has actually overheated, blown out of the cap when the temp was high.

Other than the overheating issue, the car runs very well.

People have mentioned the head, and I am starting to believe them.

Any ideas?

Did you read posts #23 and #24?

Did you understand them?

Without any more data, we have no confirmation that you even have an overheating problem.

The highest posted temperature with the IR gun is 94C.

There is no problem with anything other than the driver, and, possibly the sending unit.

Ignore these "people". They are usually factually incorrect.

I do understand them. I thought it could be my own paranoia. However, it did blow the cap and all the coolant out last week. My paranoia was confirmed. This prompted me to change out the water pump.

The old water pump seemed ok, temp still goes high on hills, I don't want to test it too much. Any help is appreciated on this. I am stumped.

Hoping the problem is the water pump and the temp sender. I will order the sender tomorrow.

It is noteworthy to mention I use all genuine MB parts

This data is is diametrically opposite to the data that you posted with the IR gun. It cannot blow it's cap and lose coolant unless the coolant boils, and that doesn't occur until the engine reaches 120°C. if the coolant is proper.

Therefore, with conflicting data, nobody can really help you with precision. You'll just get a bunch of WAG's..................

Sorry.

Well, situation has changed. It used to not register above the 110 mark or so, but one day, it actually did on a modest grade. The data from the IR gun was before the coolant boiled over. Now the coolant does boil over on hills.

I can drive on flat land forever. Car runs great. Once there is a hill though, the temp shoots straight up.

Again I will tell you that the cap releases at a pressure point, not a temp.

______________________________________________________________

I had this same problem and I spent months trying to solve it. In my case it was a head gasket. I don't know if your problem is a head gasket, but you should test for it. The whole painful thread is here : http://www.peachparts.com/shopforum/diesel-discussion/292852-cooling-system-riddle-1991-350-sdl.html

I never detected combustion gases in the coolant reservoir. This lack of gases in the coolant convinced me that it was not a head gasket. What did convince me to change my head gasket was pressure testing the coolant system while driving.

Here is what I did:

I installed a "t" fitting for the small radiator vent hose that goes to the coolant reservoir. Actually, I just removed one end of the hose, installed the "t" on the end and another short piece of hose to the radiator fitting.

I installed a pressure gauge on a piece of hose long enough to reach the bottom of the windshield in the driver's view and attached that to the "t". Use a plenty long hose so you can position the gauge where you can read it.

Went for a drive. I could watch the pressure build when the engine was under load, but not overheating, and remain stable when the engine was loafing along. I could see when the cap would release. I could see the pressure in the system the next day.
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The other thing to look at is your radiator. If it is no longer viable, it will not be able to remove the extra heat that putting the engine under load produces.

He replaced the radiator as mentioned in post #25.

DID YOU SHOOT THE ENGINE WITH THE IR GUN WHEN YOU SAW 110-120°C ON THE CARS TEMPERATURE GAUGE?

If so what temperature did it read?

My educated guess, not to be confused with a WAG, is that you have a cracked head. You have replaced everything except the temperature sender. The symptoms you describe match my symptoms prior to replacing my #14 head with a #22 head. The head on that engine does not like 120°C. Perhaps you will get lucky like Greg and only need a new head gasket. So are you feeling lucky?

I had my coolant tested for combustion gasses and none were present yet the head was cracked and warped when it was sent out for testing.

Can you perform one test, please?

Get it good and hot and then bring it home and park it.

The next morning, squeeze the upper radiator hose. Does it feel soft and easy to squeeze or is it quite hard, as though high pressure is in the system?

Now, carefully open the expansion tank cap and observe whether gas forcefully escapes from the cap when you do it. The system might be under a slight vacuum and air might rush into the reservoir. You need to pay careful attention and make a clear determination whether air is rushing out or rushing in.

Report back with result.

What happens to the pressure in the system when the coolant boils?

When the pressure in the system is greater then then vent pressure of the expansion tank cap, the cap vents it. We both know that.

My point is that the cap vents based on the pressure in the system, not the temp. of the coolant in the system. (The cap is rated at a pressure. A t-stat is rated at a temp.) Boiling coolant is a source of pressure. But, not all pressure is from boiling coolant.

My experience was that my cooling system was building up enough pressure to vent coolant out the cap without overheating. The pressure in my system was combustion gases due to a failed head gasket.

I do not know what is causing the OP's coolant venting problem. But he seems to have replaced everything that could cause boiling coolant.

So, if he is not boiling coolant to create pressure, it must be something else.

This may be a little off the topic - all MB's in that era came with belly encapsulation panels. With the encapsulation panels on, the main air exit in the engine compartment is through the big air dam in the panel right below the cooling fan. Which way the engine compartment cools better - with the encapsulation panels on or without?

Tan

'91 300D 2.5t
'87 300TDT

I'm also having the same issue. My system does hold pressure overnight, however there is no water in the oil or exhaust in the water, no white smoke during startup or missing coolant. I took it to my mechanic and he tested for the presence of hydrocarbons in the coolant and there was none.

Since we both know that the cap vents excessive pressure in the cooling system and we both know what happens to coolant when it boils, you statement is fundamentally obvious.

Hey, OP have you bypassed the EGR valve?

What does a 50/50 colant water mix boil at? My guess is somewhere between 275 to 350F. The engine has to get damaging hot to boil the coolant. Combustion gas into the head could boil the coolant locally where the 2 meet, pressurizing it and cause the cap to vent.

If you have combustion gas entering the cooling system, that alone can pressurize the cooling system enough to cause the cap to vent, you don't need to boil any coolant.

A 50/50 mix of Zerex G-05 will boil at 139°C. with a 140 cap.

Note, however, that you cannot really approach this figure without some bubbles developing.

I would agree that the engine cannot overheat at 120°C. with this setup.

I ran the car yesterday for about 2 miles; squeezed the radiator hose today and it held pressure. Opened up the cap. System is holding pressure and blowing out. I was careful to note it was not at a negative. I started the car up and noticed some smoke/steam? coming up out of the overfill cap hole immediately after starting. Could it be exhaust gas?

If you had steam soon after starting it that's not a good sign. The coolant isn't going to be that hot that soon.

I still vote for a cracked head or if you are lucky just a head gasket.

Sadly, Bio is correct.

The pressure in the cooling system overnight coupled with immediate combustion products bubbling out of the cooling system confirms that you've got to pull the head and see what you've got.

Sometimes you get lucky............sometimes you don't.


Sorry.

Agree, head or head gasket it is. Hmmm. What to do next? 602 engine? I think it fits right on the transmission. I think I can get one for 1000 with 100000 miles on it. I have 264,000 miles on this 603, so if I was to delve into the engine, I would like a rebuilt one.

Suggestions welcome.

I might pull the head.

The curiosity would kill me.

If the head is intact, I would simply do a head gasket.

If the head is cracked, I would go the route of the 602 for $1K. It's a fine engine for that price (provided you can get some assurance that the mileage is legit).

That sounds like a good economic solution. You may want to drive a sedan with an OM602 in it first. There is at least one member on here who has had 124s with OM603s and one with an OM602. He sold the OM602 because he felt it was under powered. That was in a sedan, I believe you are talking about installing it in a wagon.

I would price a good used head. One problem with that route is the while I'm in there costs can get really expensive.

On OM606 with turbo and intercooler would be nice, but that's a bit more complicated.