Heater Core blew during full throttle. Headgasket leaky?

SweetSmellOfFailure · Post by **SweetSmellOfFailure** » 25 Aug 2020, 23:01

Hello and thank you to this great community.

This is my first post but I've been getting great tips and info all along since I got my '94 850.

But today I need a little extra advice and reflection on my thoughts.

Just earlier, during a full throttle pull from zero my heater core blew, sending steam up my windshield and coolant into my carpet. I tried limping home but stopped once the temperature gauge started climbing and reached about 3/4, hopefully not having warped the head.

I did a quick inspection and it definitely is the heater core, leaking from the top down.

Now, my concern and question:

1.Am I right to assume that for the heater core to fail catastrophically under full engine load I have to have a leaky headgasket? It's the only way I can explain such a sudden increase in pressure in the coolant system but I'm by no means an expert.
So far I have not had any reasons to believe it did and I have had cars with headgasket problems and know how it usually manifests.

2.Can I circumvent the heater core by getting some 5/8 hose, remove the heater core hoses from the block and use that piece of hose to short circuit the coolant ports from the block?
Just so I can drive home and maybe test for a week if the engine took damage instead of putting a new heater core in right away, I won't need heat for another month or so anyway.

Thank you all for your help!
Philipp

Post by **abscate** » 26 Aug 2020, 01:50

No reason to suspect the head, bypass the core as noted , watch oil and coolant levels to see if they change.

callahanoffroad · Post by **callahanoffroad** » 26 Aug 2020, 05:46

abscate wrote: ↑26 Aug 2020, 01:50 No reason to suspect the head, bypass the core as noted , watch oil and coolant levels to see if they change.

^^ seconded. It's a pressured coolant system so when the core does fail (and it always does) it's usually spectacular! I used that exact same heater hose jumper method on my car when it blew at work on me.

Post by **volvolugnut** » 26 Aug 2020, 10:54

Volvo water pumps (like all water pumps I know) are centrifugal pumps. The faster they turn the more flow they make. With normal restrictions in the system, they will make more pressure at higher speed. Sooner or later, the weak point will leak at full engine speed.
Volvolugnut

SweetSmellOfFailure · Post by **SweetSmellOfFailure** » 26 Aug 2020, 13:42

Thanks all, that's exactly what I hoped to hear!

Post by **misha** » 26 Aug 2020, 15:03

Pressure in the cooling system should never exceed 150kpa....at idle,at mid throttle or wot!

It's operating pressure is UP TO 150kpa
in all rpm range,driving conditions and gas pedal position.

Hoses are the weakest points,they should blow off first.

It could be that your expansion tank cap is at failure,not allowing the system to release pressure if it exceeds 150kpa.

Post by **wheelsup** » 26 Aug 2020, 15:16

12 years ago my upper radiator hose blew out next to the block. The cam seal was leaking and over time, weakened the hose.

I immediately pulled over and shut the car off but the temp had already hit the top mark.

12 years later, still driving the car, and no blaring issues with HG.

Post by **volvolugnut** » 26 Aug 2020, 15:26

misha wrote: ↑26 Aug 2020, 15:03 Pressure in the cooling system should never exceed 150kpa....at idle,at mid throttle or wot!

It's operating pressure is UP TO 150kpa
in all rpm range,driving conditions and gas pedal position.

Hoses are the weakest points,they should blow off first.

It could be that your expansion tank cap is at failure,not allowing the system to release pressure if it exceeds 150kpa.

You are correct. I was thinking of the way the water pump works, not that there is a relief valve in the system in form of the tank cap. I was also thinking about how decades ago my Ford truck blew the heater core during a full throttle run.
volvolugnut

Post by **MoVolvos** » 26 Aug 2020, 15:47

*
Bypass the radiator core first and test before replacing the core.

*

SweetSmellOfFailure · Post by **SweetSmellOfFailure** » 30 Aug 2020, 20:06

A little update, so far the car drives normal, no overheating, compression looks ok, if not great (160/120, 250 wet/150/160/160).
I'll definitely take it to a shop once I find time, just to make sure.
Now to figure out where the oil in the turbo intake comes from...

Thanks everybody!