1987 300SDL still running hot! - PeachParts Mercedes-Benz Forum

mike2244 · #1 07-23-2017, 10:53 AM

I have an SDL with a brand new all alloy custom build radiator that is 6 months old. I am having cooling issues on hot summer days that are +90°F. I have also changed the fan clutch because it was worn after 202k miles. I have mercedes benz brand coolant in the system. I have changed the water pump as well. I have seen on other threads that its a good idea to swap the 11blade fan from a 606 to help with cooling. Is there any way to upgrade the water pump with a 350sdl or 606 pump for better cooling? Thanks mike

Junkman · #2 07-23-2017, 11:09 AM

What about the thermostat? Have you confirmed the temp with a IR thermometer?
Do you have air in the cooling system?

A shop half-fast changed the water pump on a friend's jeep. It over heated until we filled the engine through the radiator hose which bypassed the thermostat.

Father Of Giants · #3 07-23-2017, 11:32 AM

At the very worst it could be a blown head gasket.

Diseasel300 · #4 07-23-2017, 11:49 AM

What is the cooling issue? How high is the temperature going? The SDL should be able to maintain ~85˚ coolant temp (indicated on the dash gauge as dead-center) up to ~105˚F ambient temp on the stock cooling system with the A/C blasting. At 105-110˚ my SDL will start to climb a bit, but stays between 90-100˚ on the coolant gauge at those temps. Mind you this is with the A/C on (no way I'd drive without A/C in those temps).

mike2244 · #5 07-23-2017, 01:13 PM

I have replaced the thermostat as well when im climbing up a hill the temperature begins to rise to about 110-115° I do have a slight headgasket leak. I made all the repairs with my father who was a diesel tech at MB back in the 80s and 90s. The temps are almost the same with a.c. on or off. Thanks for the replies!

Mxfrank · #6 07-23-2017, 01:15 PM

What are the conditions when this happens? when idling, at speed, under load? When were the upper & lower hoses replaced?

Are you sure your fans engage? Even new fan clutches can be bad out of box. The viscous clutch should lock up around 95C. The aux fans should engage on low when a/c pressure reaches about 300 psi, which will happen a fair amount of the time over 90F ambient.

Diseasel300 · #7 07-23-2017, 01:18 PM

Quote:

Originally Posted by mike2244

I have replaced the thermostat as well when im climbing up a hill the temperature begins to rise to about 110-115° I do have a slight headgasket leak. I made all the repairs with my father who was a diesel tech at MB back in the 80s and 90s. The temps are almost the same with a.c. on or off. Thanks for the replies!

I think you've located your problem.

ROLLGUY · #8 07-23-2017, 01:19 PM

Quote:

Originally Posted by Diseasel300

What is the cooling issue? How high is the temperature going? The SDL should be able to maintain ~85˚ coolant temp (indicated on the dash gauge as dead-center) up to ~105˚F ambient temp on the stock cooling system with the A/C blasting. At 105-110˚ my SDL will start to climb a bit, but stays between 90-100˚ on the coolant gauge at those temps. Mind you this is with the A/C on (no way I'd drive without A/C in those temps).

You are describing exactly how my 350SDL behaves, and it has an all aluminum radiator. I don't think that is out of the ordinary. It is a little scary seeing the needle get to 100 on a mountain pass, but a sigh of relief happens going down the other side when it gets back down towards 85.

ROLLGUY · #9 07-23-2017, 01:22 PM

Quote:

Originally Posted by mike2244

I have an SDL with a brand new all alloy custom build radiator that is 6 months old. I am having cooling issues on hot summer days that are +90°F. I have also changed the fan clutch because it was worn after 202k miles. I have mercedes benz brand coolant in the system. I have changed the water pump as well. I have seen on other threads that its a good idea to swap the 11blade fan from a 606 to help with cooling. Is there any way to upgrade the water pump with a 350sdl or 606 pump for better cooling? Thanks mike

A 606 fan surely wouldn't hurt, and is cheap and easy to do. I am not sure the water pump is any different. Is your radiator and condenser fins clean? Leaves, pine needles and dirt in the condenser can cause lack of air flow. Is your condenser fan working properly?

mike2244 · #10 07-23-2017, 02:06 PM

Both fans engage, i replace the aux fan As well. Condenser fan works. The temperature really starts to climb when doing highway speeds 65-75 with a.c. on going up hill. Temp usually sits between 95-100 on hot days in stop go traffic with ac on. If i floor it going up hill with a.c. on the temp will just about hit 115 which has me saying a few prayers for the #14 head. Once going down the hill temp returns to 85-90

Mxfrank · #11 07-23-2017, 06:22 PM

Diesels do tend to build heat when you load them up like this. Still, the one thing I would suggest is that you check your hoses, especially lower radiator hose. At higher RPM's, suction from the pump can make the hose collapse. If the lower hose is soft or "puffy", replace it. And while the upper hose doesn't usually create a flow obstruction, when it's soft it can prevent overflow coolant from being sucked back into the header tank.

Can you explain your custom built radiator? Any information on number of rows, fin density, etc?

mike2244 · #12 07-26-2017, 11:54 AM

I have replaced all hoses going into the radiator. The radiator is 16 fins per inch and 1 rows of 1.5" tubes. The tubes are space 3/8" apart, on center.

Here is the radiator https://wizardcooling.com/1986-87-mercedes-300sdl-1990-91-350sd-sdl-aluminum-radiator/

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