Underside corrosion watch / preventative maintenance points

[Maxz]

Anyone who believes prevention is better than cure, some watch points and suggested maintenance points for exhaust, subframes, bushes etc. Only worth the work for anyone planning on running their car for the long term. As the exhaust and cat run along the nearside, these also get additional exposure to salt and other grime from gutters as due road camber, it all flows to the left.

Process:

Wash all rusted or salt/ grime covered subframe, exhaust, pipe work with ph neutral car shampoo. Rinse with clean water and leave to dry.

Use sandpaper and wire brushes to take off all loose rust down to the clean metal, usual Kurust or similar for any thick bits.

Spray treated exhaust parts and joints with high temperature paint only.

Undercoat and gloss black spray subframe parts.

Lightly slicone spray bushes, pipework and exhaust hangers (do not overdo it and mop up any excess near exhaust as potentially flammable in high quantities). This slows down the ageing process keeping rubbers flexible and less chance of cracking.

Listed in priority order (of what was showing most corrosion):

1) Exhaust gasket/joint at Cat.

2) Subframe just above exhausts (that holds the differential in place.

3) Hubs that are on the diff (that the inner boots are clamped to).

4) Base of the front shock absorbers.

5) The brackets holding up the rear exhaust boxes.

6) The differential itself and driveshafts (not really a concern as the block and driveshafts so thick would never rust through)

7) various other weld points as shown below

It’s a mucky job but either a one time or every 5 years or so task to keep the MOT warnings at bay, have fun! Before and after pics below, should be clear which is which. Best to catch it whilst it is still surface rust 🙂

 

[scudney]

Great job did you do it all yourself or ?👍

[Maxz]

1 hour ago, scudney said:

Great job did you do it all yourself or ?👍

Have access to a pit so made sense to do. Did the same to a previous vehicle I owned when it got a corrosion warning at 10 years 85k. Needed more extensive rejuvenation as the rust had set in.

Doing the IS at 5 years 18k miles, much less initial work plus stops any damaging levels of rust setting in or annual touch-ups being required. I’d say the two critical watch points are the front shocks and the joint/gasket at the base of the Catalytic converter. If either were to go (and obviously wouldn’t until much later in the life of the vehicle)  big jobs to get repaired.

Anyone with a new(er) vehicle can obviously avoid tinkering altogether by occasional jet washing of inner wheel arches, wheels and underside during winter months to keep the salt and grime off those vital parts.

[Linas.P]

Generally good list and as you said - if you planning to keep car it is worthy.

Just one exception - treating exhaust is waste of time. In my experience exhaust will always rust from inside, before it rusts from outside. Further, when it gets hot waxes/anti-corrosion sealants will burn-off from the most affected areas (they are actually most affected for the same reason - heat cycles). High heat paint - may last a bit longer, but again - it will not prevent corrosion from inside, especially for the cars which does short journeys, low miles.

The only benefit perhaps - it may make you feel better 🙂

[Maxz]

30 minutes ago, Linas.P said:

Generally good list and as you said - if you planning to keep car it is worthy.

Just one exception - treating exhaust is waste of time. In my experience exhaust will always rust from inside, before it rusts from outside. Further, when it gets hot waxes/anti-corrosion sealants will burn-off from the most affected areas (they are actually most affected for the same reason - heat cycles). High heat paint - may last a bit longer, but again - it will not prevent corrosion from inside, especially for the cars which does short journeys, low miles.

The only benefit perhaps - it may make you feel better 🙂

Good point, there are the inevitables that can’t be prevented. Was strange though the whole of the exhaust system was in very good condition bar this joint/gasket at the base of the cat, looking much more older/weathered than it’s years.

 

[Mr_Groundhog]

I haven’t yet seen mine but Im pretty horrified now after reading this thread…. Why is the car not designed to avoid this? 
it isn’t something on the service book or anything, are they assuming the car is gonna be eaten up by rust in 10 years and they don’t care? 
I found a place nearby where you can rent a garage space with an elevator so I’m planning on doing something like this early summer. 
My question is: how to wire-brush and treat the surfaces that are on the top side (if you’re underneath the car, the upper end of the exhaust or the differential for example) ??? 

[wharfhouse]

2 hours ago, Mr_Groundhog said:

I haven’t yet seen mine but Im pretty horrified now after reading this thread…. Why is the car not designed to avoid this? 
it isn’t something on the service book or anything, are they assuming the car is gonna be eaten up by rust in 10 years and they don’t care? 
I found a place nearby where you can rent a garage space with an elevator so I’m planning on doing something like this early summer. 
My question is: how to wire-brush and treat the surfaces that are on the top side (if you’re underneath the car, the upper end of the exhaust or the differential for example) ??? 

A lot of the underside of the IS 300h is hidden by plastic undertrays - one at the front, two down each side, and one at the rear, there could be more but those are the ones I'm aware of. To see what is happening with most of the underside these would need to be removed. They appear to be secured with numerous plastic fittings which may well break if taken out and reused. I've been looking into this as one of my undertrays on side is damaged and trying to decide it it's worth replacing it. 

[Mr_Groundhog]

Has anyone here tried Lanoguard?

[Bluemarlin]

3 hours ago, wharfhouse said:

A lot of the underside of the IS 300h is hidden by plastic undertrays - one at the front, two down each side, and one at the rear, there could be more but those are the ones I'm aware of. To see what is happening with most of the underside these would need to be removed. They appear to be secured with numerous plastic fittings which may well break if taken out and reused. I've been looking into this as one of my undertrays on side is damaged and trying to decide it it's worth replacing it. 

Yes, the plastic trim clips can break, but you can buy packs cheaply off eBay. Make sure you get the Toyota/Lexus specific ones, as they're designed to pop up when you push the centre for removal, whereas some others dont. Here's a link to the last lot I bought, which were 20 for £3.95

https://www.ebay.co.uk/itm/401496166850

The alternative, if you don't want to remove the undertrays, and think what's behind is relatively ok, is to use something like Dynax UB, which comes in a spray can but has a long lance attachment, which you can poke into any gaps/cavities and spray into concealed areas.

I used the Dynax stuff on the underside and wheels wells of mine. It's probably a day or so's job to do, but worth it, and figure it will last a few years, at least in the cavities and hidden spots like wheel wells. The only thing I'd add is that annually I'll spray everything underside with ACF 50. In part this is to add a little extra protection and keep things topped up, but it also creeps into any cracks and crevices that a wax won't reach. It also has the added benefit of keeping things lubricated, and so helps to eliminate any squeaks and creaks, and only takes about 20 minutes to do with a garden pump sprayer. I use a 2 litre one with a lance.

Other than that, in winter I occaasionally give the underside a quick rinse with a cheap lawn sprayer attached to the end of a hose, to rinse off any road salt.

[Maxz]

Good advice from Blue marlin. This time of year, when temperatures are not sub-zero, good practice to lance jet wash wheel arches, wheels and underside. Get all that salt off. On the rear arches wear a glove run your finger around the lip of the arch to get the crud off. In the longer term will reduce the chances of any dreaded arch bubbling, if you plan to run your is300h for the long term. I may recheck the underside next summer, if there are any new spots I see showing signs of rust, will add to this thread.

[Mr_Groundhog]

On 12/24/2022 at 6:57 PM, Maxz said:

Good advice from Blue marlin. This time of year, when temperatures are not sub-zero, good practice to lance jet wash wheel arches, wheels and underside. Get all that salt off. On the rear arches wear a glove run your finger around the lip of the arch to get the crud off. In the longer term will reduce the chances of any dreaded arch bubbling, if you plan to run your is300h for the long term. I may recheck the underside next summer, if there are any new spots I see showing signs of rust, will add to this thread.

Sounds great! take pics if you can please!