Mercedes-Benz Forum banner

41 - 60 of 65 Posts

·
Registered
Joined
·
226 Posts
Discussion Starter #42
I'll pick one up tomorrow or Friday. Checked the timing and it was retarded 10 degrees. Set it at zero and drove it around for an hour. Drove it in stop and go traffic around noon and it did get hot but didn't overheat. Temp gage went to just under 120 and I stopped to check with an infrared thermometer, which read 107. Temp at bottom of radiator read around 55. Keep striking out on getting citric acid so I'll just buy some online. I'll pressure test the cooling system tomorrow.
 

·
Registered
Joined
·
17 Posts
I have a 1981 380SL and swapped a 500 SEC engine into it. Still trying to work the bugs out of it but it keeps overheating. Here in L.A. it's been hot and traffic is bad. I can drive it for 30 to 45 minutes and the temp slowly creeps up. Once it gets to 120, it wants to stay there. The water pump and thermostat are from the 380. They're both about 3 or 4 years old but only have a few hundred miles on them and worked fine in the other engine. New radiator cap and expansion tank. I'm going to look into getting a bigger core for the radiator tomorrow but wanted to know if anyone knows of other radiators that would fit and solve my problem.
ethanol or even water-only mist system will help in a huge way
 

·
Premium Member
Joined
·
9,894 Posts
I'm going to look into getting a bigger core for the radiator tomorrow but wanted to know if anyone knows of other radiators that would fit and solve my problem.
It might be interesting to compare the core sizes of the original 380SL (or your new upgrade) with the rad that the 500SEC would have used. Better still, compare it with a 500 or 560 SL rad that would have had to fit in the same SL space.
The 500SEC engine could have had something like 50% more horsepower than the 380SL? If so, that would also mean that there would be about 50% more waste heat to dissipate. That would presumably require about 50% more heat transfer area in the radiator. Of course, the 380SL rad may have been oversized so maybe the rad does not have to be 50% bigger.
One other thought - how does the exhaust system compare with a 500SEC/500SL? That is the other way heat gets removed? Would a restricted exhaust cause overheating? Seems so according to aa1car.com :

The classic symptoms of too much backpressure include things like a lack of high speed power, poor fuel economy and even overheating. Anything that backs up exhaust pressure into the engine will also back up heat. About a third of the heat produced by combustion goes out the tailpipe as waste heat, so if the heat can't escape it can overload the cooling system and make the engine run hotter than normal, especially at highway speeds
Sorry, I know you are trying everything - just throwing these out because they cam to mind.
 

·
Registered
Joined
·
226 Posts
Discussion Starter #45
It might be interesting to compare the core sizes of the original 380SL (or your new upgrade) with the rad that the 500SEC would have used. Better still, compare it with a 500 or 560 SL rad that would have had to fit in the same SL space.
The 500SEC engine could have had something like 50% more horsepower than the 380SL? If so, that would also mean that there would be about 50% more waste heat to dissipate. That would presumably require about 50% more heat transfer area in the radiator. Of course, the 380SL rad may have been oversized so maybe the rad does not have to be 50% bigger.
One other thought - how does the exhaust system compare with a 500SEC/500SL? That is the other way heat gets removed? Would a restricted exhaust cause overheating? Seems so according to aa1car.com :



Sorry, I know you are trying everything - just throwing these out because they cam to mind.
I appreciate all help. I can find the area of the 560Sl and 500 SEC radiators but not the volume. The 500 SEC engine puts out 18% more horsepower. I'll have to check the specs on the exhausts, didn't think of that. However, it's not running hot at highway speeds. It goes down to around 100 degrees at highway speeds. The exhaust is also louder with this engine, which leads me to believe it's not that restrictive. I got the 75 degree thermostat today. It's a Stant and Stant says that the engine should run around 95 degrees with this fully opened (I know, this would be if everything else were perfect). Ordered Citric Acid today. Pressure testing the cooling system tomorrow. I met and talked to an old school MB mechanic today. He told me to test the fan clutch by trying to stop it with the engine running over 100 degrees and the electric fan on. Couldn't stop it so, according to this guy, the fan clutch is good. I feel that I'm going in the right direction, since I was able to drive the car today without it overheating.
 

·
Registered
Joined
·
226 Posts
Discussion Starter #46
I pressure tested the system today. Had to tighten a couple of hose clamps. Also appears that the heater control servo is leaking. Crap! Tightened all the hose clamps but no luck. There appears to be a seam above the hose fittings and it looks like that might be the source of the leak but I'll have to take it out to be sure. This is disappointing.
 

·
Registered
Joined
·
2,197 Posts
I pressure tested the system today. Had to tighten a couple of hose clamps. Also appears that the heater control servo is leaking. Crap! Tightened all the hose clamps but no luck. There appears to be a seam above the hose fittings and it looks like that might be the source of the leak but I'll have to take it out to be sure. This is disappointing.
Are you talking about the aux pump or the older ACC 2 climate control system?

If it's the aux pump, you can safely remove him from the system. He's a useless appendage. Find an L pipe and drop it in.

Also, make sure to remove the Schrader valves on the harbor freight kit. They cause erratic pressure readings.
 

·
Registered
Joined
·
226 Posts
Discussion Starter #48
Are you talking about the aux pump or the older ACC 2 climate control system?

If it's the aux pump, you can safely remove him from the system. He's a useless appendage. Find an L pipe and drop it in.

Also, make sure to remove the Schrader valves on the harbor freight kit. They cause erratic pressure readings.
It's the ACC ll. I've never noticed it leaking before. Right now, I'm going to do the Tide and citric acis flushes and go from there. I'll replace it with one from Mercedes Fix when the time comes. I've been spending so much money on this thing lately that I don't want to deal with it right now.
 

·
Registered
Joined
·
226 Posts
Discussion Starter #50
Find your proper timing spec for the engine (m117?). Set that first, once you've done that, Google myndex's kjet dianogstic diys. Really easy to do.

This is assuming you still have the the old fuel ECU components.

You might not pass smog with this though. I'd get ready for a visit to a smog referee to have them modify your smog requirements for the engine changeover.

Not the end of the world since you still have the old smog components and plumbing.
I'm not finding anything with this Google search. Is it spelled correctly?
 

·
Registered
Joined
·
226 Posts
Discussion Starter #51
Well I've made some progress. I flushed the cooling system with regular cooling system flush (I left it in for a week). Then drained and flushed with detergent. Engine flush fluid came out kind of brownish but there were no solids in it. I ordered some citric acid so I'll flush it with that next weekend. I also replaced the thermost with a 75 degree thermostat. Car now runs at 100 and goes up to about 110 in stop and go traffic. Once free of traffic goes back to around 100. I have a friend that used to have a 500 SEC and he said that it always ran at 100. This is also with straight water in the system. It will be interesting to see what happens with the citric acid flush.
 

·
Premium Member
Joined
·
9,894 Posts
Yes, a myth that defies all the laws of thermodynamics.

Sent from my MAR-LX1M using Tapatalk
Don't know which law of thermodynamics would apply to running without a thermostat in a Mercedes? Might be some other kind of law ;)

This site summarizes them:
http://physicsforidiots.com/physics/thermodynamics/

Regardless, some don't seem to understand that running with no TS in a Mercedes reduces coolant flow through the radiator and therefore reduces cooling.
 

·
Registered
Joined
·
2,197 Posts
I'm not finding anything with this Google search. Is it spelled correctly?
 

·
Registered
Joined
·
226 Posts
Discussion Starter #54
Sorry but I misunderstood what you were trying to tell me earlier. I've seen this and bookmarked it. I even bought an oscilloscope last month. Took the car out for another drive. This time I took the infrared thermometer and checked the temp when the gage was at its' highest. Temp was 95.
 

·
Registered
Joined
·
2,197 Posts
Sorry but I misunderstood what you were trying to tell me earlier. I've seen this and bookmarked it. I even bought an oscilloscope last month. Took the car out for another drive. This time I took the infrared thermometer and checked the temp when the gage was at its' highest. Temp was 95.
95 is great! My 380 hovers between 85-95 depending on AC usage. I think you might be towards the end of your tunnel.
 

·
Registered
Joined
·
1,048 Posts
Just a couple of things:

1. have you verified the coolant temp sender and the gauge accuracy?

2. has the water pump been replaced and has the viscous fan hub been replaced (I hope you have)?

with a 75ºC thermostat, AC on, the running temp of my 560 is 90 degrees, in 30ºC ambient.

I went through this scenario some years ago on my 107023 and ended up replacing water pump, viscous hub, header tank and cap, thermostat, and got a custom offset core radiator upgrade.
The actual culprit was the radiator, despite having had it out, reverse flushed, verified flow to be visually fine. citric flush and all the goodies.

what I learned is that the radiator itself can flow amazingly - even when it is 80% blocked.

The term heat soak is what applies here. energy going in is greater than energy being removed. so for 80-90% of the time you won't notice anything untoward.

Then one late evening, in a tunnel, you'll get stuck in traffic, the ambient is elevated, the car is idling, heat's going in and not enough is coming out.... then up up and away it goes, in an irrecoverable thermal spiral.

The auxillary fan is supposed to prevent this scenario. However, unless the flow though the hvac condensor and radiator core is unobstructed and free, the effectiveness is somewhat limited.

When the factory cooling system is correctly maintained and serviced, this temp spiral is virtually non-existent. It would have to be over 50ºC ambient before the needle hit the danger zone.

Keep an eye on your system. If it's already hitting 95 and your ambient is 30ºC or less, you still have an issue.

scrub the hvac condensor fins and hose it out (from the back) and use a stiff bristle paintbrush to clean the fins with a good degreaser and thoroughly rinse.

You've done the flush, have all new bits (so you have confirmed) and the radiator is an upgraded unit with more coolant capacity and flow... theoretically then, for a given temp at the inlet, the outlet temp should be a lot less than standard.

So the 95ºC thing is not making sense to me. Either you have an incorrect read on your sender and gauge, or the viscous fan and water pump are not up to snuff, or the header tank cap is not sealing properly and that leak you just discovered...... it will be a contributor, but if there is a leak near your heater core, have you checked under the car or on the sides of the trans tunnel where the HVAC drains are, for traces of coolant??? (UV dye in coolant will fluoresce under blacklight)

because logically, the last great bastion of overheating cooling systems is the unloved and neglected never checked heater matrix. God help you if yours is leaking...
 

·
Registered
Joined
·
226 Posts
Discussion Starter #57
Mirv,

Consider a detergent flush followed by a citric acid flush - I was shocked how much gunk came out when I did this. Also consider a radiator recore with more tubes for more heat capacity since your displacement has increased. Finally, evaluate the health of your visco fan.

None of this is easy or cheap - I fought it for 4 years.
How much citric acid did you use? I did some calculations last week and came up with needing around 40 ounces. I'm just not sure when calculating a solid into a liquid.
 

·
Registered
Joined
·
1,048 Posts
I used 1kg, in my 560. Metric cars don't like imperial measurements :D
 

·
Premium Member
Joined
·
9,894 Posts
How much citric acid did you use? I did some calculations last week and came up with needing around 40 ounces. I'm just not sure when calculating a solid into a liquid.
It's a lot easier in metric! Density of water is 1gm/cc or 1000g/1000cc (liter). Shop manual says to use 10% citric acid. So you add 100gm per 1000gm of water (1 liter). (100gm=3.527 oz)

Capacity of cooling system is 15L? So, you would need 1500gm (1.5 Kg) of citric acid powder in 15 liters of water. (1500gm is about 53 oz.) So your 40oz would be a bit weak, but probably OK!

Best to stay away from fluid oz - those 40 ozs only apply to beverages ;)
 

·
Registered
Joined
·
1,727 Posts
I bought 3 x 500g bottles from the dealership. What I remember about it was how easily it dissolved in distilled water. I was also surprised how much grit came out given the clear flush after the detergent process.
 
41 - 60 of 65 Posts
Top