Thermostat - PeachParts Mercedes-Benz Forum

Mockles · #1 10-07-2002, 09:20 AM

Overheating situation on 75 450SE. No oil in coolant, or coolant in oil. No steam from exhaust. Radiator is warm all over, but lower line doesn't get all that warm, or hot, even, in spite of the fact that the boiled thermo opens. Not sure of the temperature setting on it, so was going to get a new one and install.

I was considering doing this, but only because it worked on a Ford I had a while back. Tell me what you think....

Remove thermostat, and reassemble housing WITHOUT thermostat, refill with water but also put in a radiator flush of some sort like Prestone. Run it for the specified length of time according to Prestone, empty completely, install new thermostat, and fill.

I may get a rash of responses as far as how stupid this may be, but go ahead, I haven't done it yet. Also, should an over the counter (Non-Dealer) radiator flush be used at all?

#2 10-08-2002, 12:44 AM

While you have the radiator empty look inside the neck to see if it is calcified. You may need it boiled out and rodded. Will do wonders for circulation. Radiator flush only scratches the surface deposits

Mockles · #3 10-08-2002, 07:36 AM

Okay, once I have the hoses off to remove the thermostat I will check the inside of the radiator. It's a sealed radiator, and there is an overflow tank.

So doing the flush without the thermostat installed is not a stupid thing to do, then? Is there anything stronger that I could use maybe instead of the Prestone stuff? Something easily obtainable, maybe?

ctaylor738 · #4 10-08-2002, 10:26 AM

Have you tried "burping" the cooling system to get the air out?

When is the car overheating?

If it is OK at highway speeds, then the radiator is probably OK. If not, then you should get it rodded out as Gympie suggests.

If the problem is at idle, then the water pump or fan are suspect.

There is a monster post on the main forum that concerns a 420SEL that was overheating that discusses every conceivable cooling problem. You might do a search there.

Mockles · #5 10-08-2002, 11:15 AM

The car is overheating at highway speeds. Sitting at idle, she stays at 175, doesn't go above at all.

At startup, and while she is warming up to about 100 or 125 degrees, there are a few puffs of white smoke from the exhaust, but afterwards, nothing. There is an issue with the muffler where I can't completely close the clamp on one side, so I am hoping maybe that's just some errant water in the exhaust, maybe some dew or something like that. I have a guy with some better tools than my set and he will tighten it up or remove and replace the nut and bolt on the muffler but that's not till Thursday.

I have read a few posts regarding "burping", and even found one post that said that the 450's need burping more than anything else, otherwise overheating will result. The descriptions are somewhat vague, though, I am finding, and I am not too sure how it's exactly done, but will try to make further inquiries on that.

Also, I have access to a dead 450sel, with no damage to the front, so I was actually thinking on possible radiator replacement, but the 450sel is 150 miles away, so I would rather rule out everything else, really. I would assume there is no difference, really, in the radiators. Was also thinking on going to a drive-thru oil change place that also does radiator flushes, maybe see what happens after that.

ctaylor738 · #6 10-08-2002, 12:32 PM

Here's an excerpt from the thread I was thinking of on burping. I would try this, then maybe a good reverse flush, and finally a radiator "rodding."

Don't see much point in putting in a used radiator that may have the same problems.

Here's the excerpt:

The 4.5 is notorious for getting air pockets if the cooling system is opened. So, what you do when refilling the coolant is to disconnect the upper radiator hose from the radiator and pour the 50/50 mix through the hose. Try to hold the hose as high as possible (you'll hear it burping) and gently rock the car to "shake" it a little to further purge it. Just keep adding coolant until it flows back out of the upper hose. Reattach hose and top up, start car and put the defrost on. You'll probably see the auxiliary fan kick on if there is still an air pocket. Just keep an eye on the temperature gauge and feel the air coming out of the vents to make sure the t-stat has opened. One other note, the older sixes are also known for air pockets, the thing to do with them is to fill the coolant in, run the car and if and when the temp gauge begins to rise above the normal mark, shut it off and let it bleed itself for 15-20 minutes. Check the level in the radiator and top up if necessary. Start it back up and make sure the thermostat opens. Repeat again if still no heat.

__________________
Rgds,
Aaron Greenberg
owner, MB Classic, Inc.
Service and Restoration of Vintage Mercedes-Benz Automobiles

Mockles · #7 10-10-2002, 07:36 AM

Okay, got the 75C thermostat yesterday, will do what I gotta do by the end of the week. Worse comes to worse, I have an appointment with the independant MB mechanic near here on the 6th, so I have plenty of time to track it down.

Will also try the burping, ctaylor738, and let you know. Been busy with work interrupting my auto work. I am sure you can understand. Will keep you posted.

Mockles · #8 10-19-2002, 08:48 AM

Here's an update. Replaced thermostat and seal, burped coolant, and it seems to work for a lot longer than it used to, but still overheats. While driving around town, stop and go, it stays at or above 175, then creeps to just above, then higher a few minutes later, but holds for a longer time, each time it creeps higher. Hasn't redlined as of yet, and have been taking her out for longer and longer drives, but she creeps up to the next line after 175 and when I get paranoid enough and start heading home, she is above that mark, so by the time I turn her off I am sure she is heading that way. Have gotten her up to about 75 mph on several occasions, and she sings right along, but gets slowly hotter. All of this is with the heater full blast. Also did the radiator flush before replacing thermostat.

Questions or direction?

#9 10-19-2002, 11:59 AM

Are you loosing any coolant from the water pump weep holes?

Is your transmission fluid up to capacity?

Try running without a thermostat for awhile to see if it is a fault or take out your thermo and test it in hot water and a thermometer to see if it is functional.

You may again, need to have the radiator cleaned and rodded.

Gympie

Mockles · #10 10-19-2002, 02:03 PM

That's the thing - I already tested the original thermostat that way and it opened fine, just got a new one because they are inexpensive and I thought that might have been the problem. Tranny fluid is fine. I had mentioned complete removal of the thermostat and running it without, but no one had said anything about it. Losing no coolant from the water pump area.

#11 10-19-2002, 03:18 PM

Yep, try running without a thermostat see what that does. Also when refilling and burping the coolant, be sure to have the heater control on full hot. Does your auxiliary water pump work when the heat is on?

Gympie

Mockles · #12 10-20-2002, 08:15 AM

I am sorry, honestly, I have not even a clue. The aux fan doesn't, I know that for sure, and that may have something to do with it as well, I have found. I will give the "no thermo" a go and see what happens.

Also, now that the overheating is at least slowing down, I will check the mix of the coolant as well. Since it is slight, it may be simple...

ctaylor738 · #13 10-20-2002, 11:30 AM

At this point I would go ahead and have the radiator rodded, or replace it with one that you know is good. With the radiator out, you might also do the pump if there is budget for it.

I recommend this because you are overheating when there is plenty of air moving through the radiator, which says that the problem is insufficient movement of coolant either due to a failing water pump or a clogged radiator.

The fact that your radiator is cool at the bottom is a good clue that it is the problem.

Have also heard good things about adding Water Wetter from Redline to the coolant.

psfred · #14 10-20-2002, 11:08 PM

I would not run an M117 without a thermostat -- the opening of the thermostat closes off the recirulation of coolant through the block, with without that closing flap, too much coolant will circulate through the block and not enough through the rad. This may in fact be the problem if you do not have a factory spec thermostat installed -- there is a flat disc on the "back" (hot) side that closes off the recirc passage. I found this out the hard was on my old Audi Fox -- took four thermostats, none of which would let the thing run at the proper temp, until I bought one at the dealer. Problem was obvious at once, as they didn't look the same at all.....

Most likely, if the bottom of the rad is always cool, is that there is inadequate coolant flow through the rad, either from a dead water pump or from a clogged rad. Either one will cause exactly your symptoms. Get the rad out and have it cleaned -- the radiator shop can test the flow for you, and that will tell you immediately if it is clogged. Once you ahve a good rad in place, make sure you have the correct thermostat (I like Behr, but any other OEM is fine, too -- just don't get one at Autozone!).

You also need to check ignition timing -- I believe it should be 7 degrees BTDC at cranking speed (static), 5 degrees ATDC with vac, about 5 degress BTDC without vac. You may want to advance a bit more, but not more than 5 degrees, and make sure the vac retard works properly before setting it.

Peter

Mockles · #15 10-21-2002, 06:57 AM

Well, I removed the thermostat and drove her around for a bit, a good solid half hour of driving at various speeds. During the burping process, I removed the upper hose from the radiator and started pouring till water was running out of the upper part of the radiator. This makes me think that the radiator is fine, or would it be? It's completely warm, all over. She held her own till I got onto the highway, where she slowly rose again. Was able to get her back before redline. The thermostat is OEM and I got it at a foreign auto parts shop, 75 degree, etc. I don't recall the manufacturer, it's outside in the trunk.

Seeing how this seems to be something like a "slow leak" so to speak, would it be possible it could be a head gasket issue, and just not doing anything till after a certain temperature? I have yet to address the timing issue, was going to leave that up to the independant MB mechanic, for which I am scheduled on the 6th. Now, I know what you are thinking - "He's asking us all this stuff but didn't check the timing yet?" - I was hoping to address the overheating issue only, prior to the MB mechanic taking her over, because I got a couple weeks before the appointment.