It would seem 3 years after changing my heater core I will have to do it again. I certainly know how to do this (3 previously done). 1991 740 turbo wagon. Heater core was a four season all metal OEM copy or maybe the OEM.

I did a quick clamp/not clamped the hoses to the htr core & saw a 3-4 psi difference in a pressure system test. I am losing coolant and no sign of an exterior leak.

I want to try and delay this fix, so I was thinking of using a rad leakstop & circulate it only thru the htr core only then flush.

Anyone recommended a good (if there is)leakstop product. Are there different types or do they all solidify on contact w/ air. Do they have to be in hot coolant also.

Quite unusual for a core to last only three years. My OEM core has lasted for twenty. What kind of coolant are you using?
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See the 700/900 FAQ at the drop-down menu above right.

I've been using Zerex G5 for about 1 year. I had deionized water & a prestone (green) copy for about a week before I twigged. The 2 years before I used city water & the prestone (green)copy. I changed anti-freeze every 3 years or so before.

On both my 1991's 740 & 940 turbos I always had less than 0.1VDC coolant to ground. But I think vvpete drove a stake thru that arguement. Better to use resistance. More disolved metals lower resistance.

Anyway this is my second heater core on my 740 since I bought it used. So I assume that the first one was original approx. 11 years old. This last one a 4 seasons brand new was changed in early 2003. It now has a small pinhole, holds 12-14 psi.

I can't see how it is bad grounding. All my grounds are good (I confirmed & cleaned & lubed) plus the extras I've added.

I'm going to make a heating circulator & deposit ceramic seal (Irontight) thru my new core before installing or find a stainless one.

The car is a train, always starts, freaky little issues like that @#$%$#@ generic O2 sensor that leaked air thru the body making the car run stupid rich pop up but I'm happy with it. I cannot even begin to think what can cause my cores to pack it in so soon.

ian

boy, that is a stinker. I did this replacement as well with no issues for years. You must have a heathy back to do this again. I rather change a head gasket than change a core!

Is your floor matt wet? Heater valve working?

I would check if you have some voltage leak thru your coolant. Check the FAQ's

3 years is too quick.

FYI, I was at a electronics store in sacramento (Fry's) and they had a lighter 12v plug in heater for a car.

Hi Rob,

It's leaking. Fluid loss, I smell & taste it and a pressure test shows it. Clamped off the core & the pressure loss was less. Hard to find wet carpets because the insulation is so thick on the floor matts. I went about mad doing the coolant voltage checking. I had a high indication (over 0.1VDC)with the battery connected/disconnected, running/not running. Same reading. Verified by 2 good meters. I slapped grounds all over even though the grounds were all cleaned & checked. I figure the whole car is a battery. I gave up no.

I'm going to get some Irontite ceramic motor seal & make a circulating rig & seal the inside of a 4 season (metal)heater core prior to installing. First I'm looking for a stainless steel that will fit.

cheers ian