My 380 SEC overheated a few weeks ago. I found someone had backed into the front end and pushed the radiator into something down there. There was a small hole and, yes the fluid drained as my teenager was merrily motoring down the interstate. I bought a new radiator and installed it. The car still overheated. I removed the guts from the thermostat to try that while waiting for a mail-order thermostat. It still overheated. Next I checked the compression and changed plugs and wires as it stuttered on starting. The pressure is 145-150 except for the two cylinders near the firewall. They run at 170. It still stutters on startup and heats up slowly to the red line. Is it the gaskets? Do I get the heads resurfaced too if it is gaskets? What do you think? UnkaMike

What was your "overheat" indication? The gauge or water vapor from under the hood as in a boil over?

The first thing that came to mind was a failed water pump somehow, as in broken impeller fins.

Also, if it appeared to "boil over", it may be exhaust gas in the cooling system - indeed a problem.

Ken300D

Ken300D
Wow, thanks for the quick answer. The water pump crossed my mind. I had a new one installed at 80,000 miles and I now have 160,000. The radiator hole was down at the bottom of the fins just above the plastic base. The fan and declutching unit appear pristine so they probably didn’t get involved in the bump and run that ruined the radiator, but then, I don’t know what poked the hole in the radiator.
A water pump would be easier than head gaskets. The radiator does not boil over unless the cap is removed when it is hot. I try not to do that. The pressure relief on the cap has not kicked in. Someone suggested rigging a cap with a pressure gauge to see if the radiator was pumping up with pressure. The only indications are high pressure in the compression test on the rear cylinders and the stutter on starting. That miss cleans up after a bit. Heat is detected with the in car temp gauge. UnkaMike

Low Tech test

With the system cold, make sure full of coolant (or plain ol' H2O), leave radiator/expansion cap off. Start engine, let warm a bit and gently rev it. Often a blown head gasket will build enough pressure in the cooling system to force coolant out the expansion tank.

If a fair amount of coolant comes spewing out the tank, chances are good the gasket is blown.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

Mike

Thanks for the hint. It sounds like good ol' common sense. I will give it a try. If air comes out, it is probably a gasket. (piston pushing compression into water jacket) If water just boils its the water pump. Is that it? UnkaMike

Well, the head gasket (or the head itself) contains three things:

- Coolant
- Oil
- Compression

so if the head gasket has failed, you'd think there would have to be a violation of a boundary. So, we'd be talking about:

- Coolant leak to the outside of the head
- Oil leak to the outside of the head
- Compression leak to the outside of the head

Or some combination of the things being contained:

- Oil in the coolant - visual
- Coolant in the oil - possibly visual
- Compression in the coolant - bubbles/spewing (or coolant in the cylinder - white smoke)
- Compression in the oil - blowby (or oil in the cylinder - blue smoke)

So if you suspect a head gasket or head warpage problem, checking for these indications comes to mind.

The other thing that could happen is a failure or blockage of the oil or coolant somewhere, such as inside the head. This would lead to overheating and damage. Not all that likely to be a blockage. For oil you should still have a good pressure gauge indication and might see oil spray if you open the oil filler cap while running.

For coolant, you need good coolant circulation - especially by way of the water pump. On many cars you can open the radiator cap and verify coolant motion when the throttle is kicked. Not so on the "no radiator cap" Mercedes radiators.

I'm trying to think of what the initial overheat might damage, leading to continuing overheating - that's not the head gasket/seal. Just because the head gasket is leaking a little bit, it would not necessarily grossly overheat.

Are you overheating while driving, or just sitting there idling?

Ken300D

Ken300D
I agree with all the indications you mention. So far, the overheat is when driving around the neighborhood. I haven’t tried to let it stand and idle. The oil was just changed to synthetic when the radiator, plugs and wires were changed. There are no indications of oil, water or compression outside the block, nor any mixing in the fluids is evident. The expansion tank fluid is tough to see clearly. Oil in the expansion tank will be tough to find. The only indications are the severe missing when starting a cold engine. That clears up as it runs in less than a minute. The other indication is ballpark 150 compression on the forward 6 cylinders and 170 compression on the rear two. I have no idea how to see if the coolant is flowing. Maybe changing the waterpump should be the first step. What do you think? UnkaMike

Since you removed the thermostat there should be no restrictions on the coolant flow whether cold or warm.

An unsophisticated approach, if you don't care about spilling a LOT of coolant, is to take off the top radiator hose, prop it up, and start the engine. Coolant should FLY out of the top hose if you rev the engine just slightly.

This test is easier than taking off the water pump to check it. If you do this, be gentle with the radiator where the hose connects - its PLASTIC - AHHHHHRRRRRRGGGG!

If you do that you'll want to hose down the car and the area around where coolant spilled.

The other thing that might overheat an engine is a really lean fuel mixture. This is a little consistent with that miss you're experiencing. But I wouldn't think it would overheat around the neighborhood at 25-30 mph.

Ken300D

Ken300D and Mike
Thanks for your hints. I got home from work, topped off the coolant expansion tank and fired her up. It didn’t want to start but after a lot of cranking it turned over. The exhaust was an excessive white smoke. I think I have my answer now. I will be pulling the heads and hope it is only a gasket. Do you normally resurface the heads after overheating? Or does the gasket blow prior to head warp? I had a similar problem long ago with a cast iron engine and had to resurface the head. I think the 380SEC has an aluminum engine. Does the metal act different? Do you think that normal installation torque of the heads down will flatten them out? UnkaMike

Yes - I think you have your answer now. The coolant had time to seep into the cylinder. Well, you're beyond my personal experience now, but I'd guess the reason you have a compromise in the head integrity is because it warped.

You'll certainly know more when you get the head off. There may even be a crack.

Someone here on the forum with more experience can probably tell you what tests need to be done to the head. I suspect that once you get it off the car, you'll need to take it somewhere for some kind of inspection and/or test.

Let us know how it turns out.

Ken300D

I would suggest taking it to a reputable automotive machine shop and have it checked for warpage. If it is warped the valves and everything have to come out.

__________________
Jim

Be really careful if you try to start it again to move it or get it to the shop. If the cylinder fills with coolant you can hydrolock it and bend a rod!

If you REALLY have to start it, take the plugs out of the bad holes first.

__________________
D.H.

04 ML500
02 E430

Experience is something you don't get until just after you need it.

I heard of a hydrolock that cracked a 560 block

I had the exact same problem with mY 1997 C36.


Read my posts recently.

Getting my car back fromt he dealer this tuedsay.

Hairline crack on the head. Had it welded. Had a bas exhuast valve. Replaced. Also machined the head. The dealership got the head back and is not in the proces of re-intsalling ti and testing.

rough cost $4500 CDN dollars.

__________________
1997 Silver AMG C36
OEM Advantegarde Grille
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Eibach/Bilstein Combo
Zender Rear Lip Spoiler