1998 Volvo C70 Overheating and fog on windshield

Volvich · Post by **Volvich** » 30 Oct 2014, 23:20

Hi,
my windshield got extremely foggy tonight to the extent I could barely see where I'm going so I had to lower side windows and take a peek when needed. Turning on the fan made it worse. I could smell what I guess was coolant from the vents. And coolant temp went up a couple of notches. I was close to home so I drove carefully keeping RPMs low and watching the temp gauge. Radiator fan was working the whole time. I checked by hand the temp of large hose going from engine to radiator, expansion tank and its lower hose. They were equally hot so I believe the coolant circulation is ok.
I don't know how these symptoms are connected but I believe they are.
Could anyone give me directions on how can I diagnose this problem?
This is the only car I have right now and I need it up and going ASAP.
Any help is much appreciated!

Post by **tryingbe** » 30 Oct 2014, 23:34

Your heater core has a coolant leak.

It needs to be fixed before you over heat the engine. Drive it at the risk of overheating the engine.

Post by **stephansvolvo** » 30 Oct 2014, 23:47

Try this link.
Definitely a heater core. 40 bucks shipped from eBay.

https://www.matthewsvolvosite.com/forums ... =1&t=66581

Volvich · Post by **Volvich** » 31 Oct 2014, 00:47

Well, after I posted here I went for a test drive... not the smartest decision.. Everything looked fine, but then Temp gauge started going up and white smoke started filling the cabin :/ Pooled over, shut the engine and opened the hood right away. Called AAA and had it towed back home.
Yep, the heater core is gone.
But could you explain why it causes overheating? There's still enough coolant in the expansion tank and it seems to be circulating.

Post by **Atis** » 31 Oct 2014, 04:00

Maybe it only seems that there is enough coolant there.
The other option is, that the pressure dropped in the system causing the coolant boiling at the hottest areas, and as steam is a heat insulator compared to liquid coolant, your temp went up.

Beside these, as you had steam in the cabin, you have lost coolant, so it was just matter of seconds to have really low coolant level.

Post by **E Showell** » 31 Oct 2014, 07:21

+1 on the heater core leak. Replacement is not that bad a job, but make sure you lay a contractor's garbage bag down in the footwell area since, no matter how well you drain the system, you will have coolant leaking on the floor in the footwells.

Post by **Ben850** » 31 Oct 2014, 17:41

Volvich wrote:Well, after I posted here I went for a test drive... not the smartest decision.. Everything looked fine, but then Temp gauge started going up and white smoke started filling the cabin :/ Pooled over, shut the engine and opened the hood right away. Called AAA and had it towed back home.
Yep, the heater core is gone.
But could you explain why it causes overheating? There's still enough coolant in the expansion tank and it seems to be circulating.

The engine cooling system is pressurised. This means liquids are allowed to exceed the point of boiling through a combination of the air pressure inside the "closed system" no leaks, and the coolant type added to the water (distilled is preferred).
Breach, leaking, no longer mean the system is sealed, or pressure sensitive to atmosphere.

The heater core leak was the breach that allowed the system to boil. Steam and other unpleasant things follow.
To find steam in the cabin is an indication to not drive it until the said breach might be repaired.

The next issue becomes lack of cooling to engine, and head gasket failure. Other failures will follow.

I only wish to help to understand what I knew was happening to my vehicle.

Also, it goes quicker when a heater core hose gives up its ghost.

: I did not see this coming.

Volvich · Post by **Volvich** » 31 Oct 2014, 18:48

Atis wrote:Maybe it only seems that there is enough coolant there.
The other option is, that the pressure dropped in the system causing the coolant boiling at the hottest areas, and as steam is a heat insulator compared to liquid coolant, your temp went up.

Beside these, as you had steam in the cabin, you have lost coolant, so it was just matter of seconds to have really low coolant level.

Ben850 wrote:The engine cooling system is pressurised. This means liquids are allowed to exceed the point of boiling through a combination of the air pressure inside the "closed system" no leaks, and the coolant type added to the water (distilled is preferred).
Breach, leaking, no longer mean the system is sealed, or pressure sensitive to atmosphere.

Thanks, now I get it!

So glad replacing heater core isn't that hard to do. Ordered yesterday the part from Ebay (thanks to 'Stephansvolvo') and will be getting it on wednesday. I might go and try to pull one from a junkyard tomorrow, to get the car running until I get the new part.
Is there anything else I should consider changing once I'm at it?

Volvich · Post by **Volvich** » 01 Nov 2014, 19:12

Overheats again!
Coolant boils after idling for 5-7 minutes. I was concerned that I may have air trapped in the system. Let the car idle with open cap, and when the coolant started to go up, closed it. Same results, coolant is boiling... any ideas? Blown head gasket?.. Coolant color is a bit yellowish, is that a sign of exhaust gases getting into it? I've noticed that before though, when everything seemed to be working fine...

Post by **E Showell** » 01 Nov 2014, 19:26

Bad coolant expansion tank. Get one from dealer only. Aftermarket ones are notoriously in reliable.