W123 Cooling system explanation - PeachParts Mercedes-Benz Forum

guyonabuffalo · #1 02-23-2015, 08:13 PM

Hi PP friends,

W123 noob here. First off, thank you to everyone here for all the amazing information and posts etc. I ve been a W123 300D driver/owner for a year now and she is pretty much everything I know about cars, diesels specifically; thanks to the awesome folks here.

I ve recently been having cooling issues, erratic temperature gauge readings and random temp stabilization episodes. A few weeks ago, while being stuck in traffic, I noticed the temp needle climb frighteningly so I pulled to the side and shut the car off. Once it cooled, it looked like there was no coolant; nothing. Filled it with whatever water I had in the car and drove back immediately.

Ever since, the car seems to be running hotter than normal. Although this is a totally random experience since it will sometimes run hot if I warm it up and get on the highway, or random runs to the shops, or run perfectly at slightly above 170F without wavering.

I understand that changing out the radiator, thermostat and pump might be the best thing to do since they are all suspect at this point, I would like to try a few things first and am hoping to get some advice from you guys.

First, I would really appreciate if someone could explain what the additional radiator infront of the main radiator is for. Its the smaller radiator with the auxiliary fan. I m thinking of cleaning the fins of the radiator as thoroughly as possible and this thing is obviously in front of it. Although it looks like a radiator, I m not sure its allowing enough air to reach the actual radiator.

Second, I have a new thermostat that I ve boil tested; purchased a new water pump as well; should I do a cooling system flush before installing either? It seems like some people have had weak points exposed after a flush ; thus multiplying the initial problems etc. Would a flush be advisable?

Third, has anyone figured out a way to attach a digital temp gauge? Is this advisable? I dont think I trust my gauge very much since an infrared thermometer revealed that its sometimes inaccurate. I d rather not take the instrument cluster off to change the gauge. Would prefer to just have an additional accurate gauge available.

I ve read through all the cooling system threads and have been left with these questions. she ran nicely today but the next ride could be totally different. I sincerely appreciate all your feedback.

dkr · #2 02-23-2015, 08:38 PM

Your immediate problem is that you are loosing coolant.

DO NOT DRIVE YOUR CAR ESPECIALLY ON THE HIGHWAY UNTIL YOU ISOLATE THE CAUSE.

It's not your thermostat that's leaking, so we can rule that out.

If you turn the car on from a cold start, can you see coolant dripping out? If so, isolate the location. It is probably the water pump. If it is your water pump, don't drive it even a mile. It needs to be replaced immediately.

Likewise if your radiator is leaking, it needs to be replaced immediately. A drip will turn into something larger and usually when you are on the freeway and before you know it you will be shopping for another engine.

If you can't see coolant dripping out, you can rent for free a coolant pressurizer at AutoZone or NAPA. When the engine is cold connect it and start pumping pressure into the system. You should start seeing coolant coming out somewhere -- that is unless you have a breached head gasket.

Forget about straightening fins or putting in a digital gauge or doing a cooling flush. Your immediate problem is that you are leaking coolant somewhere and the car needs coolant in order to run at operating temperature.

Dkr.

charmalu · #3 02-23-2015, 08:38 PM

Welcome to the Forum.

The small radiator is for the AC., and has nothing to do with the Cooling System.

There could be debris caught between the two radiators, and or the fins could be plugged with debris also.
Best way is to drain the Radiator, remove it and blow out the fins on both Radiators.

Before you start throwing a lot of money at it. Check the grounds.
There is a ground strap from the body to the engine on the drivers side below the Oil filter housing.
Remove the bolts and clean the contact areas. I had this same problem with my Temp gauge, and it was this ground connection.

Charlie

pj67coll · #4 02-23-2015, 08:47 PM

Quote:

Originally Posted by guyonabuffalo

I ve recently been having cooling issues, erratic temperature gauge readings and random temp stabilization episodes. A few weeks ago, while being stuck in traffic, I noticed the temp needle climb frighteningly so I pulled to the side and shut the car off. Once it cooled, it looked like there was no coolant; nothing. Filled it with whatever water I had in the car and drove back immediately.

Ever since, the car seems to be running hotter than normal.

Random erratic temperature needle fluctuations don't sound like an actual cooling problem but more like an electrical problem. How often did you check your fluid levels before you found no water in the engine? By that I mean could it have been in need of coolant for a long time and you finally noticed it when the temperature spiked or was it a fairly sudden coolant loss?

Since that incident how often have you been checking the coolant level and how much have you had to add?

- Peter.

Skippy · #5 02-23-2015, 09:57 PM

Quote:

Originally Posted by pj67coll

Random erratic temperature needle fluctuations don't sound like an actual cooling problem but more like an electrical problem. How often did you check your fluid levels before you found no water in the engine? By that I mean could it have been in need of coolant for a long time and you finally noticed it when the temperature spiked or was it a fairly sudden coolant loss?

Since that incident how often have you been checking the coolant level and how much have you had to add?

- Peter.

Bingo. Start with answering those questions and we will have a better idea of what the problem may be.

BillGrissom · #6 02-25-2015, 03:19 PM

The temp gage reads abnormally high when there is air in the system, like say from a coolant leak. It probably is high right at the gage, since sitting in hot vapor, but the engine may not be overheated. After filling, you need to do some tricks to get all the air bubbles out. Driving the front up on ramps and idling the engine might work. Then you are ready for an oil change too.

A coolant flush is always smart. Citric acid works good. If it starts new leaks, it hasn't really damaged anything, just exposed already corroded areas that were ready to fail. It could simply be leaking from the electric "aux pump" shaft seal. If so, just replace that silly thing with a section of heater hose. It does little good and can cause the dash to overheat and start a cabin fire.

Re playing with the thermostat and gage readings, lookup my post where I did so, and applied careful tests to resolve that my gage read correct and my T-stat wasn't up to snuff.

guyonabuffalo · #7 02-25-2015, 04:06 PM

So none of my responses are posting here. I ve been watching the guage as keenly as possible. For whatever reason, it seems to be not as erratic since my original post. I m not sure what to say. I did take some pictures an hour ago of the position of the gauge and infrared thermometer readings of different places under the hood like top of radiator, hoses, thermostat housing etc.

guyonabuffalo · #8 02-25-2015, 04:13 PM

I must also let you know that once I pulled over and was done taking the photos, I noticed a little bit of coolant dripping from the overflow hose that comes out from below the radiator cap and hangs down to the side of the fan shroud. Based on this and the above temperature readings, could it be that I slowly lose coolant this way and this accumulates over time?

guyonabuffalo · #9 02-25-2015, 04:20 PM

Big thanks to all of you. I think I will get the system pressurizer and try that out, it seems like a great way to test a lot of different sections of the system. I will update as soon as possible.
Thanks again.

guyonabuffalo · #10 02-26-2015, 08:51 PM

So, for the past couple of days, the temperature gauge seems to climb normally with only one sudden spike which has since cooled and been normal. It doesnt seem to waver much beyond the mark on the photo I posted above; however I noticed - after pulling over today- that there was a drop or two of coolant below the over flow hose. Coolant overflowing implies that the system is hotter than the needle would suggest; thus extra hot/pressurized coolant is being expelled. Is this normal? Does this mean that now my gauge is totally inaccurate? Am I wrong in my assumption?
I m assuming this is probably what has been happening for a long time, which led to my total coolant loss incident. All other components in the cooling system dont seem to have any obvious signs of leakage. I will try to get the pressurizer over the weekend and see if that reveals anything.

guyonabuffalo · #11 03-01-2015, 05:58 PM

Hi folks, updating as promised. Yesterday I changed the thermostat and coolant with new Zerex coolant - the 50/50 premixed kind. So far the system seems to be running cooler and there has yet to be any sudden temperature spikes like before. I will test the old thermostat today to make sure that was the culprit. I understand this is a short fix and I still might have a tiny leak somewhere. Eventually I plan on replacing the radiator with a new one as well as a new water pump - pretty much overhaul the whole cooling system with a higher capacity electric fan etc.
One thing I did notice while down there was a rusty looking line coming out of one of the round circular plug type indentation on the engine block closer to the bottom. Which implies that something leaked out of there thus making the rusty line. Its hard to check on this spot since its so far down but I will do what I can.

guyonabuffalo · #12 03-02-2015, 04:18 PM

Boil tested the old thermostat and sure enough, it only opened a little bit near 200F.

Maxbumpo · #13 03-02-2015, 04:36 PM

Sounds like you need a new radiator cap for sure, as well as the new thermostat.

Leaking coolant needs to be addressed and fixed...

cooljjay · #14 06-17-2015, 10:32 PM

I had just posted about the evil servo climate control in another thread of yours. A look into your statistics shows you have a common problem also seen in the 1978 model.

This model has an evil servo climate control just google it for tons of info, below is the servo and this one shows a crack in the side. This is probably what caused your coolant leak some months ago.

This year also has a bleed screw on the thermostat housing. The cooling system needs to be bleed.

My thought is that there was air in the system causing the over heating from the servo leaking coolant..