I did a search and couldn't find a thread with the specifics of how to get around a leaky heater core. I'll be looking at a used 1993 190E that has a leaking heater core, and if I like it would need to drive it home about 50 miles. One thought I had was to put vacuum on the heater valve behind the engine wall with a mity vac to keep the valve closed. But if the valve is faulty, I'm out of luck. Can someone tell me the hose size, both length and ID that I'll need as well as clamps and adapters to perform this bypass? Thanks

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'81 300SD

I had to do this on an 87 190D, obviously it is not exactly the same.

I used a 3 foot section of 3/4"/19 mm ID heater hose. Ran the hose from the end of the heater coolant feed pipe over the top backside of the engine to the heater coolant return engine connection. The feed pipe in that configuration ran from the waterpump/thermostat housing at the passenger side front of the engine back towards the rear of the engine on that side. I disconnected the hose which connects the feed pipe to the vacuum control heater valve at the end of that pipe. If you know the hose clamp is in good condition you can reuse the one that is there, if not bring a good one with you. Attach the hose to the pipe and run it behind the engine over to the passenger side. Find the outlet from the heater and follow the hose from that to wherever it connects back to the block on the driver's side of the engine. Disconnect the hose from the heater from where it connects to the pipe or bib going into the block, get the hose situated so it's not rubbing or interfering with anything and you can close the hood, the you can cut off any excess and secure it in place with another good hose clamp. I ended up cutting about 6 inches of extra hose off the original 3 foot section to get everything to fit well. Bring whatever tools fit your hose clamps (benz factory clanps are usually 7 mm) and it will be easier if you have about a foot of extentions to reach down to where the end of the pipes and the hoses meet, otherwise you've got to reach your hands down inbetween stuff and that can always be a problem. Bring some premix coolant or water to top the system up as you'll lose some small amount of coolant when you disconnect things opening the system. A couple nylon tywraps to hold anything in position if needed and you should be good to go.

Thanks Mark, Did you use an elbow fitting to keep the hose from kinking when coming from passenger to driver's side? Was the 3/4" ID a snug fit or kind of loose?

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'81 300SD

On the 190 D the passenger side pipe it angled up and slightly out at it's end so the hose doesn't need to bend much and on the driver's side the pipe is parallel to the ground but there was enough room to allow a wide (maybe 10'' in diameter semicircle) 90-180 degree bend to get the hose on it without it wanting to kink.

As I recall the 3/4"/19 mm ID hose was a Goldy Locks "just right" very close fit, I had taken the factory hose to the parts store with me when I got the generic heater hose an compared them side by side.

Just went out and took a look at it, it's labeled Gates 3/4" (19 mm) Premium Heater Hose.