95 850 Turbo Heater hose leaking at firewall

[dtmmoore2]

I just had a replacement engine swapped into my car. Installation went fine until it came time to add the coolant which resulted in it leaking badly at the firewall connection. In removing the engine I understand my new mechanic simply disconnected the two heater hoses at the engine leaving them attached at the firewall.

Just to back up a little bit, last winter I had the heater core replaced by my regular mechanic. I ordered the part myself and it seemed to match up perfectly with my old one. After installing it, the mechanic checked for leaks and found none. He did not touch the inlet and outlet heater hoses running between the engine and the firewall as this was not necessary to install the new core.

Four months later, through a combination of bad luck and a different mechanic who let me down, my engine managed to overheat and I had to find a replacement. There was apparently a leak in the cooling system but it was not definitely determined where it was although I had suspected it was at the water pump.

However, my new mechanic told me (and demonstrated) that when he connected the heater hoses to the engine and added coolant, it began to leak out at the connection between the lower heater hose and the tube running through the firewall (is this tube part of the heater core itself?).

At first it seemed like the problem lay in the fact that neither of the two rubber O-rings were found at the site of the connection of the lower heater hose. However, he later found one in the tube that the lower heater hose inserts into. Where the other one disappeared to I will never know but I think it must have been there or I would have noticed coolant leaking out at the connection and onto my driveway long before this. The plastic clip was broken but I don't know if that contributed to the leak or if it broke as it was being manipulated by my mechanic when he tried to find out the cause of the leak.

Once I had assembled all the pieces to make the connection (a new clip, two O-rings, a plastic ring, and a plastic washer that sits between the two O-rings) my mechanic connected the lower heater hose by pushing it into the tube in the firewall until it slipped into place. He then added water but it quickly began to leak at the connection.

To make matters worse, in trying to solve the problem my mechanic pulled the upper heater hose out from the firewall for the sake of comparison and in doing so he broke part of what seems to be the plastic tube running through the firewall. However, while it was not pressurized, the system only leaked at the lower heater hose connection.

I don't know what to do next. My mechanic says that the recently replaced heater core needs to be pulled and probably replaced. In the meantime he is anxious to test the motor as this job has been dragging for weeks now. He suggested that he will bypass the heater core somehow (I assume by fashioning some type of tube connection between the two heater hoses.) and that we can look at it again once winter is on its way.

I would really appreciate any thoughts on what could be causing the leak given that the lower heater hose sits snuggly in the tube with all the rings etc. and the clip properly in place. Could the new heater core which seemed to have been installed correctly and without any leaks be a possible cause? Is the core the same design for both turbo and N/A engines? Would it make sense to try taking off the small metal plate where the hoses meet the firewall to help resolve this?

Thanks,

Davis

[abscate]

It is documented here that even the OEM Volvo heater couplers have yellow plastic snap ins that have the wrong depth. This might have been the source if the leak

[dtmmoore2]

Thanks for the info. I pulled a replacement white plastic snap off of a wrecked 850. Exactly the same as the original broken one. I also picked up a yellow plastic snap off another wreck that is longer (greater depth) than the white ones. I just assumed it was not the correct one and used the shorter white one. Since the white plastic snap was working well for a number of years with no leak at the heater coupler, can I not assume that it has the correct depth?

[dtmmoore2]

Also here is a copy and paste of part of the heater core replacement tutorial It mentions removing the metal plate. I don't get it This plate was not removed when the heater core was replaced nor did it need to be removed in order to disconnect the heater hoses from the coupling after the leak was noticed when my mechanic tried to refill the coolant system that had been dry (that's why the engine overheated and needed to be replaced) up until that point.

Step 12
Now for the fun bit!! In the engine bay push both heater hoses clips while pulling on the hoses to remove the heater hoses. Have a bucket under the car to catch the coolant or if your engine is dirty & you don't want to contaminate the coolant just tie them up pointing up.
Step 13
In the engine bay loosen the 2 torx screws (In Pic that hold the metal plate over the heater coupling and remove the plate by prying it off with a flat screwdriver. Push the coupling back through the firewall and while doing this rotate it 90 degrees (this is the key to getting it removed easily)