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.