[greydelacruz]

Hi all. My dad, my girlfriend and I are trying to restore a 76' 450 SL (156k miles, 3 speed auto). There are a few issues with it that we're not sure what are.
The issues it has are:
1. Very slow throttle response.
2. ALWAYS have to pump gas to get it to start, I don't know if this is necessarily an issue, but I'm wondering if that would point to something bigger.
3. If it idles for more than a minute after reaching 175 degrees it seems to choke out and die.
4. It's leaking coolant, we can't seem to find where from exactly, is there (in general) a part we can replace to fix that issue?
5. Brakes squeak a bit, it's not a big deal but I'd like to get everything in mint condition at some point
6. The speedometer bounces up and down when moving (especially at lower speeds)
Thank you all ! we're all new to this but I can't wait to learn more and more.

 

[WhiteSpyder]

1,2, 3 and 4 may be related. Pressure check the coolant system for a leak. If you can’t find one then you might have a head gasket issue. At 175 or so the thermostat opens and coolant enters engine. If the head gasket is leaking coolant into the cylinders that is can cause those issues.

 

[andyslc]

Fuel pump problem, under the trunk floor
Fuel filter dirty, next to the pump.
Fuel fiilter in the bottom of the gas tank.
Head gasket leaking.
Cracked vacuum line somewhere.

 

[Retired and Loving it]

Do the pressure test as recommended by WhiteSpyder, Not sure how much coolant you are loosing but pull the spark plugs and see if there is moisture/rust on any plug if there is then it's probably head gasket if this is not obvious then disconnect cables as you would for a compression test on a 450sl and with wide open throttle turn engine over and see if moisture is blown out of a plug hole best done cold after the car has sat all night. What colour is your engine oil, milky? Is there moisture or milky oil deposit on the inside of your oil filler cap, if yes to these then its a gasket or head problem.

 

[greydelacruz]

Update: checked oil, not milky or watery. My dad has pretty much neglected the car from day 1, and has mostly just given it to a mechanic and asked em to check it out. The mechanic he told me about was EuroTune in Chesterfield, VA. From what I've heard, they're not very good. Today I decided to look at it myself. Missing front top passenger side engine mount. Cracked and rotted cooling hoses. I saw one with tape on it, touched it and it literally broke when I did. There are a bunch of cut wires (not by an animal, as if someone cut then with scissors). The fluid line for the windshield washer is also cut, for some reason. I also sat in the car today for about an hour trying to get it to stall at idle, it never did. However, what it did do was sit at around 175 degrees for 20 minutes, then start to climb in temperature and that's when the car started to leak coolant. Anyway, thank you all for the responses but as of now I don't think it's a blown head gasket. I also need to check the fuel pump tomorrow, I heard if I just switch the key one notch and not actually turn it on, I should be able to hear it from under the car. I don't know if that's true or not, anyway thank you all !

 

[Retired and Loving it]

If you say it is leaking coolant then it should be easy to see where it is leaking from. How much coolant do you loose in say 10 minutes? Is there a pool on the floor and if so where is it dripping from? Are you getting steam out the muffler?

 

[greydelacruz]

If you say it is leaking coolant then it should be easy to see where it is leaking from. How much coolant do you loose in say 10 minutes? Is there a pool on the floor and if so where is it dripping from? Are you getting steam out the muffler?

Yes there is a pool on the floor. It loses probably like 1/12th of the whole thing in 10 minutes or so. It starts dripping directly under the engine block, then after shutting the car off, the leak starts coming from right in front of the engine block. I didn't notice any steam coming out of the exhaust however. Though at around 175 degrees there was steam coming out of the engine bay.

 

[andyslc]

Yes there is a pool on the floor. It loses probably like 1/12th of the whole thing in 10 minutes or so. It starts dripping directly under the engine block, then after shutting the car off, the leak starts coming from right in front of the engine block. I didn't notice any steam coming out of the exhaust however. Though at around 175 degrees there was steam coming out of the engine bay.

I really don't want to say this but you are going to have the complete cooling system, radiator and hoses etc. Replace all hoses and get the rad' tested. Put them all back and try again. If you still have steam and leaks then it's an engine out job complete clean, head off and check everything.
You'll need a couple of strong mates as well.

 

[greydelacruz]

I really don't want to say this but you are going to have the complete cooling system, radiator and hoses etc. Replace all hoses and get the rad' tested. Put them all back and try again. If you still have steam and leaks then it's an engine out job complete clean, head off and check everything.
You'll need a couple of strong mates as well.

Thank you, that's what I figured. Do you think it would be better to try and take it to a mechanic that ACTUALLY knows what they're doing? I think we could get it done, it's just a matter of do my dad and all my friends want to. I want to, but I could definitely not do it myself.

 

[Retired and Loving it]

If you want your friends to remain friends and in your position I would take it to a reliable mechanic, ask this forum for one in your area maybe someone will know of one if not Google Merc mechanics. Ask them to put it on a lift (something that you have not been able to do yet), so that they can show you where the water is coming from, crack in block, failed head gasket, warped head, drain plug, welsh plug, hose, or whatever, get an estimate, then post, with photos, straight away the diagnosis on this forum so you get some sound opinions on what they want to do for you and the costs of it.