Aston Martin DB4 Mk5 - Cooling, Carburettors and Overdrive | Tyrrell's Classic Workshop

Video Description

In this episode, the blue Aston Martin DB4 previously featured in an earlier episode is now joined in the workshop by a second DB4, this time finished in green. Though these two cars appear similar at a glance, Iain takes the opportunity to point out the subtle yet telling differences between them, reflecting changes made during the production run. These include variations in bodywork detailing and mechanical specification, offering a useful reference point for enthusiasts and restorers alike. The discussion turns to early reliability issues that affected not only the DB4 but many high-performance cars of the era, particularly when exposed to prolonged high-speed running on roads such as the German Autobahn. Iain explains why these issues arose, especially in relation to engine temperature control and lubrication, and describes the engineering responses Aston Martin implemented to improve durability. The 3.7-litre straight-six engine’s aluminium construction is also explored in detail, with particular attention paid to the cooling system and how it manages heat distribution within the block and cylinder head; essential knowledge for anyone interested in the mechanical makeup of the DB4. Out on the road, Iain carries out a standard post-workshop test drive, using it as an opportunity to assess how well the car performs in real-world conditions. During the drive, he answers a frequently asked viewer question: what is the difference between an SU carburettor and a Weber carburettor? His explanation covers the operating principles of each, their strengths and weaknesses, and why a manufacturer might choose one over the other. Rounding off the episode, Iain also gives a clear and concise breakdown of how overdrive units work, explaining the mechanism by which they reduce engine speed when cruising, and why this system was once a staple of British motoring design. He also touches on the reasons overdrives are no longer common in modern vehicles, highlighting the evolution of gearbox technology. For those seeking a deeper understanding of the Aston Martin DB4, classic carburettor systems, or the workings of overdrive gearboxes, this episode provides a wealth of insight, all grounded in real-world application and hands-on experience. Join this channel to get access to special TCW Member perks: https://www.youtube.com/channel/UC2pQT90JBqbMHSVLtbJBvyw/join This video was brought to you by Howden - https://www.howdengroup.com/uk-en/tyrrellsworkshop For a free valuation from Hampson Auctions, please click https://hampsonauctions.com/tyrrells-classic-workshop/ Follow Iain on: Instagram: https://www.instagram.com/iain_tyrrell/ X / Twitter: https://www.x.com/iaintyrrellcars = = = = = = = = = = = = = = = = = = = = IMAGE CREDITS Sourced from Wikimedia Commons unless otherwise stated.