Help!
GENERAL
CM comps
Q The last few issues of Car Mechanics have had competitions that can only be entered by a browser, not a search engine. What’s a browser? I have tried all sorts but can’t get anywhere – help!
C W Beck
A The browser is the name used to describe the web page used to access the internet. The link in the competition needs to be entered into the web address bar in the same way you would when typing in any website you wished to visit.
The web link in the August issue was https://bit.ly/3huCrgp and this needs to be typed exactly as it is printed adhering to the upper- and lower-case letters.
Once typed in the address bar on the web page (browser) then it should go to the page showing the competition.
GENERAL
MIG welding
Q I have, what I hope, is a simple request. If I’m MIG welding a car with ECUs (say at least 10-years-old) do I need to unplug all or some of the ECUs, or is it enough to disconnect the battery?
Dave Roberts
A It is quite sufficient when MIG welding any part of the vehicle to simply disconnect the battery, this prevents any back feed from the welder from finding its way into the electrical units. It is also advisable to ensure that the earth lead from the welder is as close to the point being welded as practically possible.
This cuts down the danger of the current in the weld circuit affecting any of the vehicle components. Welding surge protectors are available which allow the battery to remain connected, but I always feel happier disconnecting the battery rather than rely on such a device.
GENERAL
Dielectric grease
Q I bought a few years ago Permatex dielectric grease to prevent corrosion on electrical connections. Does it lose its dielectric properties over time and should it be used within any specific time frame? Also, is it safe to use on high current circuits like starter motor, glow plugs or alternator to prevent corrosion or oxidising?
Bartosz Kijanski
A Dielectric grease is also known as silicone grease. It is a non-conductive grease used to protect the electrical connections and to help the transfer of heat.
It can be used on all electrical applications that you mention in the vehicle such as starter motor and alternator terminals to help prevent corrosion.
It should not lose it insulation properties over time and should last for many years.
GENERAL
Synthetic oil
Q I always use brand name fully-synthetic oil and I am worried that, like milk, it may get too old to use.
Ed Cahill
A The general consensus is that stored in an air-tight container at an ambient temperature synthetic engine oil has a shelf life of around five years. It is always wise to shake the oil container before using oil that has been stored to help ensure that the additives which may separate over time, are evenly distributed.
Provided the container is tightly sealed the opportunity for condensation or water ingress from the atmosphere will be reduced and so should not be an issue.
GENERAL
Jump-starting
Q Would it be possible to do an article/piece on the jumpstarting of vehicles? There seems to be mixed advice out there, some VMs stating ‘not to do it’, others stating ‘connect +ve lead, start donor vehicle, then connect -ve lead’ (Mercedes).
Some suggest using jump leads that have an integral surge arrestor. Some advise ‘turn on recipient vehicle HRW or headlamps prior to disconnection of jump leads’. Some comment regarding ‘damage to Gel or AGM batteries’.
Would be great to have some clarity from the experts, namely yourselves. Thank you.
Rob Packham
A Jump-starting used to be such a basic solution to a flat battery. If the vehicles battery was flat you could come along with another vehicle and connect up the leads and
away you go. I will even admit to using two batteries in series giving 24 volts to boost an old 12-volt diesel van into life many years ago, something which should never be considered now.
Modern vehicles have computer technology controlling many operations. The problem with the computer technology in motor vehicles is that it requires a stable voltage and is easily damaged by any peak or surge. The modern smart charging system does not help in this respect as if it detects a sudden change in voltage it will adapt to suit and can then create its own surge of unwanted voltage. This can happen connecting or disconnecting the jump leads from a running vehicle.
Forgetting the basic problems which can occur if the jump leads are connected the wrong way round (yes it does still happen) I regularly hear reports of systems not working only to discover that the vehicle had recently been jump-started, or the owner had kindly jump-started another vehicle.
Given the problems that can occur it is much easier for the manufacturers to just say don’t do it. This saves the problems, and whilst some may be lucky and get away with a quick jump-start disregarding the recommended procedure, when a problem does occur it will often be expensive.
The ideal situation is to replace or charge the battery or use a jump-pack such as the one from the NOCO Boost range. These units are made mistake-proof, and feature spark-proof technology, as well as reverse polarity protection, but of course not everyone wants to spend £80 on a glovebox ornament they may never need. Jump leads are a bit cheaper.
I would also recommend not getting the cheapest jump leads available. The low current flow and the high resistance of some of the cheaper leads makes them a poor choice, and when you do put a load through them, they are likely to become hot creating another hazard.
So here is the procedure I recommend: The donor vehicle needs to have a good battery and it also needs to have been started and be running smoothly. With both vehicles close enough to connect the leads, and with the ignition turned off on both vehicles the leads can be connected up. The positive (+) lead should be connected first to both the positive terminal of the flat battery and then the donor vehicle. The negative lead (-) is then connected to a good earth point on the donor vehicle then the vehicle to be started. The reason for the lead not being connected to the battery directly is that as the circuit is completed or broken when the lead is connected or disconnected a small spark may occur, and if this takes place it is better that it does not occur near the battery. It is also the case that if a battery condition monitor is fitted, this will be fitted to the earth terminal on the battery and using the chassis as a ground will negate the possibility of damage to the monitor.
Many modern cars whose battery is housed in the boot or under the floor will have convenient jump-start points specifically for the purpose which does make the
