AIBU to resist replacing our old cars despite my mother-in-law's comments?

Her comments on your finances are unreasonable as it is nothing to do with her, but it likely comes from a place of caring about your safety. There is no way I would be driving children around in an unreliable car- you hear of so many horrendous situations that happen when stopped on a motorway hard shoulder. You don’t need to break the bank but scrimping on a family car is never worth it if you have a reasonable alternative as you seem to.

Cam belt or alternator belt?

My cam belt was well within the service interval (only vehicle I've cared enough about to get the belt replaced on), but the alternator belt tensioner failed, the alternator belt started flogging and got shredded, shreds of alternator belt got wrapped around the camshaft wrecking the timing, and crash bang wallop. Engine went from perfectly fine to dead in about 10 seconds.

Which was nice.

(Sorry, auto trauma dump 😳). So it could have been a lot worse!

It's none of your MIL business so I would just ignore her.

I wouldn't replace until one of them regularly starting breaking down. When DH owned his car (he gets a work one now due to where he works) we always replaced it when it started to cost us a couple of hundred more than twice a year.

First post nails it.

and I wouldn’t waste my breath on anyone who thinks ‘what’s the point of money if you drive an old car’. Having money gives you choices, once you have spent it, those choices are gone.

So long as your DH is on board, then a simple ‘that would be nice’ is all I would bother saying to MiL.

For what it’s worth, I earn plenty, have been very blessed with inheritance and drive a 2006 model with 167k on the clock. I look after it, have it serviced regularly by someone who knows what they are doing and says what a pleasure it is to work on a ‘real’ car.

Choices. I really value my choices and hope you do too. Don’t let someone who has no idea take those choices away from you , or even rob you of your contentment.

I do this. I’ve got a whole parade of 0% cards. Borrowing cash at 0% and investing cash at 8% is one thing when it’s from a credit card provider but a 0% loan from your mum in cash she could earn 8% on is quite another. It’s sensible to have some easily accessible money if you want to buy a campervan on short notice.

Over 10 years old and with a lot of mileage…I wouldn’t be keen on what could happen on the motorway with kids in the back tbh.

@FudgeFudy so OP keeps all her money tied up but then expects parents to have some spare cash lying around for them to use, so parents can miss out on having interest on that money

Maybe I’m just less bothered by other peoples opinions (I don’t think it’s an assumption that underinvesting in your actual lifestyle to the point that your break down twice in a short period of time may be a worse idea than spending maybe £3k more on transport or having 1-2 vehicles instead of 4 - it’s an opinion. It’s a different opinion to the OPs opinion but I just think that’s fine. I don’t even have the same opinion as my own DH in loads of things, let alone the same opinion as our parents and kids). I’m comfortable chatting about money with people I’m close with. I understand not everyone is but I don’t understand why you don’t understand that other people are. The OP is interested in investments and is life-planning rigorously for early retirement and comfortable talking to parents about borrowing cash so it’s safe to assume money is an open topic for her - until someone else has a different opinion.

Exactly. It's quite savvy to bung all you can into a S&S ISA and have very little in cash. I've never had any 'cash in the bank' other than my salary, everything is in equities compounding nicely. If I've needed extra cash quickly I've used zero % credit cards. If push really came to shove I'd sell some shares - it's not like it's tied up in a horribly illiquid property investment - but in 20-odd years I've not had to. If the OP's parents are happy to advance them a small loan then that's up to them, and again makes sense from the OP's perspective.

What doesn't make sense is having two vehicles you don't use festering away, just get rid of the campervan and the Eos.

Mine is 2 a year

Her comments probably stem from concern about safety and reliability. That's a sign of love. It's not like she is nagging you to change car every year to keep up with the joneses. Could be a false economy to keep old cars runnning as they need constant repair. Why not trade in and get new cars - more efficient probably - on an HP scheme? And I agree with her - no point in 100k in bank and unreliable vehicles. You are saving for later while ignoring significant needs in the present.

You both wfh and have 4 vehicles? And none is really reliable? I mean you do you but I'm raising an eyebrow and I'm not related to you !

This isn’t to lecture as I didn’t know this until recently and my garage told me

But a cambelt going at 100k miles isn’t really bad luck. They have a limited lifespan after which they need replacement. A cambelt snapping on the motorway is dangerous and usually if it gets to the point it snaps it damages the engine.

If you’re only spending £300 a year on maintenance for such old cars are you doing enough maintenance? I have an old Volvo and think it will go on for a while but it’s needed things like brakes replacing etc.

"100k in the bank and borrowing money off your parents when in your mid 30s"

it all depends on how the £100k is invested and how much interest is being charged on the £3.5k. A stocks and shares ISA could be returning 8% tax free, a limited access cash ISA will be 4%+ tax free. As to buying a new car, if it's a Jaguar-Land Rover product you can almost guarantee it will spend more time being repaired than driven, that is if it's not been stolen to provide parts for another one.

Talking about investments, yes, totally normal. Talking about exactly how much money you have in investments generally not a good idea imo because people start to make assumptions as shown by OPs MIL.

Why don’t you have cash in the bank? Or is this just due to maternity leave?

Money is literally the only thing I talk to my mum about. She isn’t interested in anything else. Even people with normal parents probably talk about what investments they’ve made and life plans and breaking down in the motorway. Is it not normal?

We had two old cars. They were both 2011 plates, one approaching 100k the other much lower mileage. We make sure that we stayed on top of maintenance getting belts replaced at 70,000 as recommended, servicing them every 10,000 or 12 months, batteries got replaced at 10-12 years old and so on.
At the end of 2024 my car (low mileage) spent 6 weeks off the road for a simple and cheap problem to fix but with a short supply of replacement parts. At the beginning of 2025 my partner car started with issues. We did the repairs but decided that as we now had two cars that were starting to need more on going repairs, and this car not quite working for us as much as it did at the start, we replaced this car. We bought a 2022 plate estate with low mileage with cash. This is our main car and my car is very much the spare car which does about 3-4000 miles a year. We have decided that we will keep my car until it breaks or our mileage per year goes up. We will probably replace it with a 5-8 year old car with low mileage. We will run both cars for as long as possible

You aren't unreasonable for having older cars but I would say you are unreasonable in loaning money from family to buy a car with so much in investments. You are leaving yourself vulnerable to life events with the balance you have in accessible and unaccessible money. What would you have done if one of the problems with the car was terminal and you had to buy another? What would you do if your boiler broke? I would be looking at moving enough out of investments to pay off the loan to your parents and to have the balance of investments to cash something like 90:12 rather than the 100:2. I would look at having one slightly newer car /lower mileage car so keep the car in the best condition currently and replace the other one with a 5-8 year old car with 40-50k on it. Plan on running both cars until they break replacing each time with a 5-8 year old car that's relatively low mileage. This should allow you to play leap frog and always have an older and newer car.
The problem we found with having to older cars was the risk of having both needing repairs at the same time. It means there is a newer car to use on long/motorway journeys. We are driving to France this summer and we would have felt more hesitant doing this in our old car. We have too children and whilst a 1 year old is fairly ok on the side of a motorway for an hour a 3+ year old is a liability.

100k in the bank and borrowing money off your parents when in your mid 30s

That's sounds more entitled than people starting I'm struggling to live on my 100k salary threads.

As for the cars you've broken down twice on the motorway. If you're not going to buy a new car, at least with a young child stay off the fucking motorway. They are about the most dangerous places you can ever be in those circumstances

Apart from anything car related, why is your MIL party to you and your DHs financials? That's the bit I don't understand.

You get 20 year old cars and older on motorways all the time!

Saying that OP, if I had the money I'd say cars that are 2012/13, had 100k on the clock and are starting to cause issues are ripe for replacement. (My van is from 2012 with 90k on the clock, I have had a very expensive few months with it (new engine among other things 😱) but I can't afford to replace it).

I would sell the camper van- it just sounds that you're not getting enough use out of it to justify it. You could always buy a cheap caravan instead and get a towbar put on one of your vehicles- cheaper, more flexible and less to go wrong. I would also sell the car you've got sitting on your drive and at least one of your ageing cars, pay your parents back and buy something from about 2018 onwards with say 50k on the clock or less. If you've got a driveway maybe go for an EV to cut running costs?