I have been having problems with the last 2 batches of the expansion tanks.

In fact I have 3 count'em 3 defective new ones at my shop and no way to get a refund.

The problem with the 1st of the last 2 batches was they used the wrong early mold for the upper half. The difference being that the early expansion tanks use the same low pressure cap as the earlier pre-expansion tank radiators. The early caps are limited to only 7 lbs and they have a 1" reach and the caps aren't easily available. And not only did they use the wrong upper half, they did a very poor job of bonding the upper half to the lower and the process left a very rough sealing surface. So rough that not even the 1" cap would seal on it.

So the 2nd, and AFAIK the current batch, was made the same as the 1st batch, with the early 1" deep upper section but they tried to bond in a 1/4" spacer on top of what I am assuming is the unusable 1" surface. Problem is they did a very bad job of bonding the spacer and the expansion tanks leak around the outside of the spacer where the cap doesn't seal. And 1 of the defective tanks I have, the spacer ring actually fell out before I could even sell it.

The later expansion tanks are supposed to have a 3/4" reach and IIRC the correct style of caps can be had in pressures exceeding 20 lbs The correct style of 3/4" reach caps are not hard to find although I haven't found a 11 lb aftermarket cap to match the Volvo original cap so I use a 13 lbs which almost every auto parts store has in stock.
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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com