’95 E300D – Do the heads tend to crack on overheated 606 engines? (like an early 603)

[RunningTooHot]

I went to look at a car that’s beautiful; unbelievable for the miles on the car (over 300,000). It’s in excellent shape except for one problem, and it could be a big one. The car ran hot – at a range of 95-103 (peak). This is with the air conditioning on & at speeds ranging from about 50-70 mph on an 80 degree day. I pulled over to check the auxiliary fans, and they were not on. It has a new (very recent) radiator. This leads me to suspect that perhaps the old radiator failed catastrophically (broken radiator neck?) when the fans didn’t kick in & the pressure built up. It seems very likely that the engine overheated when that happened.

So now my concern is if the head gasket is bad. I checked the upper radiator hose before I started the car, and there was no residual pressure, but the car hadn’t been driven for several days either. I checked again about 45 seconds after the engine was started, and there was still no pressure build up in the hose. But the car runs hot…

I don’t mind the idea of taking a chance on having to change the head gasket, but I don’t know if the 606 engines have a tendency to crack their heads like the earlier 603’s. A valve job & head gasket are one thing, but buying a head casting is another!

Any input would be greatly appreciated!


Glenn

[joe p]

Well, if it does not pressurise the cooling system right off, odds are its ok, at least the seal from the combustion chamber to the cooling system is. If the car is not mixing oil in the coolant (or viceversa) try replacing the thermostat and double check the accuracy of the guage/sender. Aux fan function has several players, the switch in the head, the a/c switch, relays, resistor and of course the fans and wiring. Check the fuses, they are either in the box or in the relays in the back of the box. (simple test, turn on the key and jump the a/c switch, if you get a/c clutch, jump the other switch) I've not seen a 606 with a cracked head as of yet and 103C is not really that hot. I'm inclined not to be too concerned until I see 115C myself. (my old 617 runs normally in the 100 zone at 75 mph, been that way for 200K, the old 103 in the wagon runs in the 105 zone in traffic)


The 603's I've seen with cracked heads (all of 3) were losing coolant with no explanation, just simply eating it. No excessive pressure, no trails and they would pass a pressure test with flying colors, however and a gas analyzer would get hits in the 5000 PPM range off the cooling system with pure water in 'em. There is also a simple, inexpensive tester that uses a chemical that changes color in the presence of HC/CO in the cooling system.



Joe

[psfred]

Aux fan should be on and the visco clutch locked up at that temp. I'd replace the visco clutch and find out why the aux fan won't run before getting too excited.

My 300D runs 100+ in slow traffic with the AC on, never had a problem yet.

As stated above, cracked head will show cold coolant tank pressure, oil in the coolant tank, water in the oil, or "mystery" coolant loss.

Peter

[RunningTooHot]

PsFred: Good to “see” you again! I’m laughing… “don’t get too excited” I guess that I’m sensing a bit of deja-vu with this situation – perhaps you may recall that when I bought my ’84 300D I had the same overheating symptoms & it ended up being a cracked cylinder head (yes, on a 617!)

I failed to check the visco clutch on my test drive (I didn’t even check the fuse – duh!) but I’ll dig into it when I pick up the car on Monday. I’m glad to see your reference to similar temperatures with your 603; perhaps the 124 chassis diesels just tend to run a bit hotter than the 123 chassis.

Joe P: So far there is no evidence of leakage. I’m going to run down all the items that you mentioned right after I go get the car on Monday. The fans should have been on due to two triggers; both the coolant temperature & the AC receiver/dryer temperature switch. Some of the later systems are new to me, such as the auxiliary fans using a resistor – I’m assuming that the speed is variable, controlled by the resistor?? I’m used to the old binary system – On or Off via a simple switch & relay.

I just ordered the service CD’s, so it’s “off to the races”…

Glenn

[psfred]

Higher temps are normal, especially in slow traffic with the AC on.

Aux fan is two speed -- AC receiver/dryer switch (pressure, not temp finally) goes through a resistor, so you have low speed with AC. Engine temp sensor "switch" (actually a thermistor that goes very high resistance) switches high speed.

The contacts on the resistor tend to corrode --its up by the headlight on the 300D -- and that can keep the fan from running via the AC switch.

Visco clutch should lock up at about 90 C ambient, release at 85 or so (may be 5 degrees higher) -- coolant temp will be around 100.

The newer heads are MUCH less likely to crack than the older ones.

Peter

[RunningTooHot]

That’s the type of useful information that can make life a lot easier for me! This is the first 124 chassis that I’ve owned, so I don’t know the locations for many components, or how some of the newer systems work. I’m looking forward to learning about these cars – I can hardly wait for the Service CD’s to get here (hopefully they are better than the ones for the 107 & 123 chassis cars!)

Thank you again for the information!

Sincerely,

Glenn