w108 4.5 overheating issue

[ambush276]

My W108 4.5 eventually goes above 100C and keeps climbing when i am sitting in traffic. It does not go there really fast... but i notice it starts to climb consistently in traffic and sometimes i have to pull over and shut it off for 30 minutes or so to let it cool down (when it goes over like 110c). If i am driving at night without traffic it seems to stay nicely between 85-95c. What i have done.


1. added a high CFM pusher fan in front of the condenser.

2. Flushed and burped the system.

3. drilled 2 small 1/8" holes in the thermostat.

So far nothing has solved this traffic problem. The radiator fins look fine. I doubt it is a faulty temperature gauge as that seems to be also ok. Is the slow rising in traffic indicative of a bad water pump? Beyond that... I am not sure what else to do to fix this problem.

--Sam

[Diseasel300]

You could certainly have a worn water pump. You could also have a partially clogged radiator. You could also have an engine that's not running quite right (lean).

Something else not mentioned is a possible bad fan clutch. The engine driven fan moves far more air than an electric pusher does.

Next time the temp starts climbing, give the engine some slight RPM (1000-1500) and see if the temperature starts to come down. If it does, suspect the water pump has a worn impeller.

[Graham]

Check your timing for a start.

Set it to about 27-30BTDC at 3000rpm. At idle with vac connected it will be something like TDC-+5degBTDC. These engines run hot when retarded and the NA setting cause timing to retard at idle (for emission reasons). Car will run better all round if set as above.

If you can't get the timing to advance, distributor may not be in correct position or the internal centrifugal weights may be stuck.

[JMela]

One can test the fan clutch by sticking a rolled newspaper into the moving fan. If the fan is stopped or significantly slowed, time for a new clutch.

Have you checked your thermostat to make sure it's opening normally? If it's old, replace it.

[ambush276]

thermostat is ok.. I tried the fan clutch by basically harnessing the fan so that it is always locked (just for a test at idle). That seemed to make no difference after like 5-10 minutes the car was already over 100c (from cold). If i am moving at highway speeds consistently it seems to peg fine somewhere in the 85-95 range and sits there.. but once i start to go back to stop and go it will creep up.

I thought about cleaning out the radiator.. but i am nervous to do a citric acid flush as i assume it will harm some seals on the engine (at this age).

I am guess i am asking is this slow climb at idle usually related to a bad water pump, clogged radiator, or bad timing. I had the timing checked about 8 months ago and it was fine (as well as the timing chain/tensioner) by a proper vintage mercedes mechanic. So i would be surprised if it has gone bad since then.

[ambush276]

Originally Posted by Diseasel300

You could certainly have a worn water pump. You could also have a partially clogged radiator. You could also have an engine that's not running quite right (lean).

Something else not mentioned is a possible bad fan clutch. The engine driven fan moves far more air than an electric pusher does.

Next time the temp starts climbing, give the engine some slight RPM (1000-1500) and see if the temperature starts to come down. If it does, suspect the water pump has a worn impeller.

when you say lean... do you mean the octane of the fuel?

[Tomguy]

Ultimately if you're overheating in traffic it's a flow issue. Unless it's really hot out (35C or more) the temp shouldn't even get above the 100C mark on your gauge. I remember my 4.5 stayed at 175F, which is your 80C mark, on all but the hottest days, and rarely got more than halfway between 80 and 100C (175 and 212 for us US cars).

The flow issue may be a few things:
1) Faulty water pump,
2) Bad radiator,
3) Bad fan

You've addressed #3 by adding a pusher fan. Even with a bad mech fan clutch, a high CFM pusher fan SHOULD keep it cool enough in traffic (I assume you are not referring to the OEM A/C fan but a more robust one), so let's look elsewhere.

Have you done the water pump lately? Even if not leaking, after 4+ decades of pushing coolant and sitting in coolant, the fins corrode. You may not even have fins left on your pump.
The radiator can (and will) calcify on the inside. This means that although the fins on the outside are clean and fine, the inside isn't flowing. A good radiator shop can boil it out clean for cheap, and then leak-test and fix leaks on it after the process. You will need to find a shop that does both, before having it boiled, because you don't want to have to have it fixed by another shop after.

I'd start with having the radiator boiled out, because you say it cools off once you're moving. This sounds like the radiator isn't able to cool due to limited surface area. A faulty water pump shows up at all speeds as it can't keep the engine cool regardless of RPMs and flows, but the fact that your temp isn't getting to - and staying at - 80 (or actually lower, since you drilled the thermostat) is still cause for concern, honestly.

Edit: Lean running can cause issues, but from MY experience in lean running and having bad timing, it shows more at speed than idle. The cooling system is robust enough at idle to handle lean.

[ambush276]

i will try boiling out the radiator. Will have to go to someone here who can actually do that... Do they have to take the radiator off of the car and whatnot? I was thinking of buying a new pump.. but maybe i will just try the radiator first.

[Graham]

Originally Posted by ambush276

I had the timing checked about 8 months ago and it was fine (as well as the timing chain/tensioner) by a proper vintage mercedes mechanic. So i would be surprised if it has gone bad since then.

If they set it to the US figures in the book, the engine WILL run hotter. In South Asia? Hard to say which numbers they would have used. Has distributor been touched for any other reason since timing was set? Easy to re-check and set. A lot cheaper than boiling rad or new pump but it's your car, so good luck New radiator core may be what is needed if coolant system was not maintained.

[Graham]

Originally Posted by Tomguy

Edit: Lean running can cause issues, but from MY experience in lean running and having bad timing, it shows more at speed than idle. The cooling system is robust enough at idle to handle lean.

Tom - this car is in Asia it seems. But if it has vacuum retard at idle like NA cars and the timing is set such that at idle is more retarded than TDC, the engine will run hot at idle. It's designed to do that to reduce emissions. Not so good in a hot climate with an aging engine and cooling system.

The original water pump has a rugged impeller. No "fins" to corrode away. Some aftermarket ones have fabricated impellers with sheetmetal "fins". To be avoided! Here is picture of an original impeller removed after over 40 years of service in my M117 (because of leaking seal). Replaced with Laso which appears to be same as OE.

[Rialas]

I've had the same issue.
I removed my radiator yesterday to send it off to be re-cored.
Someone had pointed out to me that it had been re-cored in the past and they hadn't used the correct amount of cores when they did the work, causing a low flow.
It's something that I never would have noticed had it not been pointed out.

[Rialas]

As you can see, not enough cores to fill the space of the rad body. Someone took the cheaper option.

[ambush276]

i guess i have to take it to a radiator specialist. I will drain the coolant this weekend and pull the radiator off and see if there is something i can do to that affect. It sounds like the water pump is ok (nothing is leaking... fluid stays correct).

Is it safe to do a flush throughout the system... or on a car this old.. only touching the radiator is advisable?

[Tomguy]

It is not only safe to flush, I'd say flushing it out if it hasn't been done properly recently is safer than not doing so. MB recommends citric acid to flush.

[ambush276]

but won't a citric acid flush harm seals. I would assume on a car this old... doing that kind of flush might be dangerous to some engine components?