Before we go further, let me say that the small tubes of the Intake manifold, which connect to the muffler, direct heated air to the aluminum-blanketed portion of the Intake manifold. The aluminum, which acts as a “heat sink”, quickly heats and transfers its heat conductively to the steel manifold, below the carburetor. The heated manifold pipe helps to vaporize the air-fuel mixture which is headed to the cylinder heads.
Where each small pre-heat tube departs the engine compartment to connect with the muffler, provides an opening where heated and/or exhausted air can enter the engine compartment—as well as opportunity for precious intake air to escape the engine compartment, thus robbing the Fan which is supplying cooling air to the oil cooler and across the cylinder and cylinder head fins.
Volkswagen invented a method for blocking this opening: the heat riser or pre-heat tube cover.
These are right and left, with 3 holes each for securing using engine tin screws.
Since metal-to-metal doesn’t seal well, and, since we are dealing with heated air, provision was made by Volkswagen engineers for hot-temperature insulation. With time, this asbestos (I assume) insulation becomes impregnated with oil and dirt and begins to fray. With each removal and replacement, the insulation further deteriorates and the insulating property lost.
Wolfsburg West markets an insulation kit just for this purpose: Part# 113-119-597. The kit contains enough pieces for one pair of covers (enough for one engine).
In all of my years of working with VWs, I have not had opportunity to completely restore a heat riser cover! I’ve always been blessed with good covers which, when cleaned and repainted, were good as new. But, my time came this past week as I sought to do some engine-tin-cleaning. Whoops!
Richard, at Wolfsburg West, assisted me with the order. Cost of the kit was $7.50 plus shipping. (note: in order to spread shipping costs, order multiple items) Richard shipped the part USPS Priority. It was here in a couple of days.
I noted that the thin metal insert in genuine VW Cover Insulation is unnecessary with this replacement kit, since there is a new metal stiffening strip embedded in the new insulation material. Also, note that the new material is not asbestos but has the same or similar properties.
I removed the old insulation and scraped away residue. If you are going to clean using a blasting technique, removal of oil and grime is essential to keeping the medium as clean and viable as possible.
I scraped and picked to remove stubborn dirt and rust from the seams and crevices of the Covers. I used sandpaper to do the rest.
Using a steel block, a small hammer and a couple of flat-ended drifts, and pliers, I straightened dents and bends. I cleaned both covers using compressed air, followed by a good washing in mineral spirits. Paint ready!
I did multiple coats of rust inhibiting black paint. The weather was hot so each coat dried quickly, enabling me to paint the covers in record time.
I hung each cover on a bent wire and left them for a few days so that the paint could cure.
Now came the simple task of installing the insulation. This is straight-forward.
The result, as you can see by the photo, is very pleasing. My car will love the attention it receives from everyone who views the improved engine compartment.