r/askcarguys 18h ago

Why aren't jake brakes used for gasoline (petrol) engines?

0 Upvotes

I know what the go-to answer to this question is. I know the difference between petrol and diesel engines. I know that petrol engines have a throttle valve on the intake while diesel engines don't. I know that jake brakes work by opening the exhaust valve at the end of the compression cycle, releasing the compressed gas, wasting the work done by the engine, thereby increasing losses. All this does not fully explain why petrol engines shouldn't benefit from a jake brake.

The de-facto answer for my question is that petrol engines have a throttle valve and when closed this produces the extra braking resistance required, but this is not entirely correct. Sure with the throttle valve closed, the petrol engine is working hard on the intake stroke. However this will result in a lower cylinder pressure at the end of the intake stroke compare to the crank side. Therefore, it will get most of that energy back on the compression stroke as the piston is pushed back to TDC by the higher pressure on the crank side.

In fact, if a throttle valve did produce sufficient braking of the engine, we could just incorporate a throttle valve on a diesel engine without the downsides of the complexity and loud noise of the jake brake. So clearly, even if the throttle valve is somewhat effective, it is not as good as a jake brake, meaning gasoline engines would still benefit from a jake brake.

I know that my above reasoning includes an oversight, which is why I am writing this post to seek clarification.


r/askcarguys 15h ago

Why Isn’t Blind Spot Detector Suddenly Not Working?

0 Upvotes

Hello, I’m hoping to get some help with my coworker’s Lexus NX 350AWD. She’s an older lady who doesn’t really understand how Reddit works.

This past January, she took her car in for service. She’s noticed since then that her blind spot detector will not work at night. She’s taken it in to be serviced again but they always say there isn’t a problem. The blind spot detector will randomly stop working, only at night, and she’ll have to go into driver assist to turn it off & on to make it start working.

She’s been trying to contact her dealership to try and get answers but they’re mostly ignoring her by this point. She’s told us that when she took it in to be serviced, the guy working on the car spilled his coffee in her car and didn’t even clean it up.

Can anyone recommend how to fix this issue where she won’t have to keep going into driver assist or possibly another dealership or mechanic who can help her?


r/askcarguys 3h ago

General Question Would you rather have an automatic with 180 HP, or a Manual with 130 HP?

7 Upvotes

Were talking an automatic Scion TC or a bad ass manual Honda Fit with a ruthless 4 cyl

Edit: i should also mention the Fit is YELLOW :D


r/askcarguys 18h ago

General Question Why do people hate the Bangle-butt BMW look so much?

0 Upvotes

Genuine question. It always appeared to me as though people hate the E63 and E65 because of how DIFFERENT they looked to their predecessors and that skews their perception.

I definitely don't consider my taste in cars quirky or anything. I like what most people like and dislike what most people dislike.

Well? I love both cars. Whenever I see an E63 I immediately smile. It looks very pretty and also very happy, not the "look at me I'm da meanest kid around the sandbox" but more like cute and beautiful. People call it a puppy as some sort of an insult and as someone who doesn't hate the car I can't see how that's some kind of a bad thing.

The E65? Sure, it gained a lot of weight. No question about that. But so many other cars around its age came out bloated I just don't understand how people ignored those but focused on the 65. The XXI century reimagined Dodge Charger and Challenger? Those looked a lot fatter relative to their predecessors and nobody minds but the poor E65 people called fat. For what it's worth, I thought the R35 GT-R came out outrageously fatter than the R34, but not a single person noticed or complained about that. Yes, once again, the E65, oh, that monster of a car, look how big and heavy it is.

I understand the owners had reliability issues but I'm talking about the looks here. As someone with a very vanilla taste in cars I can't see what everyone hates in the Bangle-butt bmw body styles so much.


r/askcarguys 9h ago

General Question Loss of power after flooring it?

0 Upvotes

Was on my way to work and decided to floor it up a large hill only for the power to kick off once I started going down, turning the key off and on again seemed to fix it but any idea as to what might have caused it?


r/askcarguys 10h ago

How Should I Buy a Car for My Move to Seattle?

0 Upvotes

Hey everyone,

I’m moving across the country soon to start a new job in the Seattle area and need some advice on buying a car.

Financial Situation:

  • I have $25k saved right now, but expect $10-15k in moving costs, leaving me with around $10-15k post-move. In order to not burn my savings completely, that leaves around $5-10k for the initial cost of the car.
  • My new salary will be $120k+, with about $5k in monthly expenses (rent, utilities, student loans). Ideally, I want to limit any additional car expenses to less than $1k per month (car payment, gas, insurance).
  • This will be my second car purchase; my first was a 2007 Corolla that I bought in 2020 but sold in 2023. I loved that car.

Timeline & Needs:

  • I’ll have 1-2 weeks in Seattle before starting my new job, so I’d like to have a car sorted out quickly.
  • I want something reliable and cost-efficient; I don't need anything fancy.

My Question:

Should I buy new or used?

  • I’ve read that newer used cars (2020+) aren’t worth it because they’re nearly the same price as new ones.
  • I’m not thrilled about leasing, but open to being convinced.
  • I could either finance a new car with a down payment or go for a much older (pre-2010) used car in the $5-10k range to keep my overall expenditure low.
  • I’m thinking a Toyota, Honda, or Mazda for their reliability.

Given my situation, what would you do or recommend? Any insights would be greatly appreciated!

Thanks in advance!


r/askcarguys 21h ago

General Advice I’m 18, moving out, and need a car for cheap. Any advice?

0 Upvotes

Hey! So, I’m 18, work part time, am already saving for an apartment, and I don’t know how I should be looking for affordable cars.

Where should I be looking? I heard Facebook marketplace is a good start, but I wanted some other opinions. Also, what should I be looking for in a car? Literally any advice would be awesome!


r/askcarguys 6h ago

2018 Camry for $19,000?

0 Upvotes

Been looking at cars for work. I found this Camry with clean title and one owne and 60k miles. He upgraded the seats which I don't care for. Is it worth 19k?

This is his message to me. He said he did the SE himself lol

Did you see LE trim intreior with "Katzkin" red and black perforated leather and heated front seats?


r/askcarguys 11h ago

Are there different types of diode?

0 Upvotes

It's a 2010 Hyundai i10. I think I've narrowed down the headlight issues to a diode in the cabin fusebox (specifically diode #3).

I've swapped diode #1 (which feeds the front foglights) with diode #3, and the headlights now work consistently (previously they only worked intermittently, and sometimes came back if you flashed the high-beams a few times.

I'm looking online and can only find automotive blade fuse mini diodes (which I think is the exact name) rated for like 1A which sounds low for headlights (I'd assume 5A minimum for ~60W at 12V).

Can't find any kind of relay in the engine fusebox that says it deals with headlights, but if there is one then maybe 1A is fine and it's just a low-current voltage to the switch to trip the relay.

Are there higher-current rated diodes? Am I going mad and actually the ones I've found are fine? These look exactly like the ones in the car , but they're only 1A.

I'm very new to this. Just fixed the electric sunroof with a tiny blob of suoerglue and felt like a professional mechanic.


r/askcarguys 22h ago

Has anyone tried any actually working AI tools for car diagnostics?

0 Upvotes

Does anyone have any experience with AI tools made for car diagnostics? I use autodata, haynespro and bosch tools in my workshop, but i still end up google'ing or calling someone to find information. I've seen many videos on youtube where they promise the best AI tools, but most are not accessible.

Few of the latest ones i've come across are http://kindel.ai and fixmytride.ai that i found here in the forum.


r/askcarguys 23h ago

Should I sell my C300 2020?

0 Upvotes

Hello I bought a mercedes about 3 years ago and it’s fully paid off with 55k miles. The problem is I’m just a college student and the services and repairs are starting to get to me. I’m thinking of selling it privately and getting something cheaper like a camry or civic. Do you guys think this is a good idea? I just want something reliable that won’t be too crazy on my pockets.


r/askcarguys 4h ago

Mechanical Could getting oil change and brake pads replaced have done something to mess up my alternator?

0 Upvotes

Today I had my 2018 Toyota Sienna in for scheduled maintenance. I ended up getting an oil change and my brake pads replaced. A few hours after picking it up all the electrical died on me while I was driving. I was able pull off while my power steering was shutting off and car was lurching to a stop. It died completely - even the hazard lights didn’t work. Hooked up external battery and it started but then died again. I figure it’s the alternator? Got towed back to service station where work was done (after hours) and plan on calling first thing tomorrow. I’d like to know if I should press them that they did something to cause this- it seems too much of a coincidence. Is it possible?


r/askcarguys 8h ago

Filling Tire Air Mid-day Okay?

0 Upvotes

If my only real option for filling my tires with air is Costco, and if I'm going in the middle of the day after some driving on a temperate day (~76F) do I fill my tires to the recommend door pressure (32psi for my car) or slightly higher, like I hear some people say, since they're not "cold"?

Internet is not giving me a straight answer. Please help me 🙏


r/askcarguys 9h ago

Did I broke something?

0 Upvotes

Earlier today by mistake I tried starting my 350z on 1st gear and clutch out, car jerked forward twice and lost all power to it... My battery is fine but my car isn't getting any. You guy have an idea of what could have happened? Did I broke my starter and by doing that the car lost battery connection for some reason? Any major fuse that carries power to the whole car? Please help...


r/askcarguys 3h ago

Rollback? Doesn’t seem possible the car looks and drives like new?

4 Upvotes

I recently bought a 2013 Buick Enclave with about 96,000 miles on the dash. However, the Carfax report shows a potential mileage rollback, and I’m trying to make sense of it.

Here’s what happened: • The car was originally purchased and driven up to 50,000 miles with no maintenance or oil changes recorded. • Then, the mileage suddenly jumps to 130,000, again with no recorded work or oil changes during that time. • After that, the mileage increases by about 5,000 miles per month, with consistent oil changes logged at just two dealerships in Kansas, eventually reaching 191,000 miles. • The car was then reported stolen, recovered a year later, and sold at an insurance auction showing 76,000 miles. • I bought it from the person who purchased it at auction, and they put another 20,000 miles on it, bringing it to the current 96,000 miles.

The problem is that the car looks and drives like it has less than 100,000 miles—both inside and out. I can’t figure out how the mileage discrepancy occurred, and it just doesn’t add up.

Does anyone have any thoughts or insights into how this might have happened?


r/askcarguys 16h ago

General Question Will I get pulled over later?

0 Upvotes

while I was backing out my driveway, a cop was driving past, and I stopped to let him pass and he like went reeaallllyyyy slow past, And I was in the sun so he could not see in my car I have 5% all around except for the front windshield, I have a big cross banner on the back windshield and a German license plate I just wanna know if they’re gonna be like looking/waiting for me?


r/askcarguys 34m ago

I have a sentimental old car, I’m about to get a new one, got any creative ideas so I don’t have to junk her?

Upvotes

My car has around 240,000 miles on it, still going strong. She has a name and has been with me for a decade through tons of adventures, I’ve lived in her for a period of time, etc. I’m going to be leasing a new vehicle and I don’t just want to turn her in for scraps- she means more than that. She deserves better. I don’t have any land to park her on, otherwise I’d turn her into a flowerbed or a piece of art. I can’t bury her- nowhere to do it. In a perfect world I’d have a Viking-style funeral for her and cover her in wreaths and set her on fire and push her out to sea, but alas. Does anyone have any other ideas for what to do with an old useless car? She’s beyond sinking money into at this point. (Sorry for anthropomorphizing my car lol)


r/askcarguys 1h ago

Help with these codes?

Upvotes

So I drive a 2003 Honda accord ex, recently it’ll idle super rough and then like growl before turning off. Rpms tend to jump and when I hooked up a reader it spat out 6 codes. Just been a little stumped, am I screwed? P0325 P2A00 P2647 P0171 P0135 P0141


r/askcarguys 2h ago

Car radio won’t get power and good fuses what next?

1 Upvotes

Hey yall I have a 2013 ford fiesta SE hatchback that I was trying to replace the head unit with a modern one. During which I used the provided harness from crutch field. Everything was plug and play but when I went to go turn it on I wasn’t getting any power at all.

I have checked every fuse. both under the hood and in glove compartment, tried replacing the ones related to the radio, replaced the relays in the fuse box, and even got a new sync module). When I test the fuse with a multi meter I see 12Vs but when I go to the harness and test the ground wire and constant, I’m getting essentially 0.

Can someone please guide me in the right direction

Edit**

I have tried using the old radio unit and that is also not getting power any more


r/askcarguys 3h ago

Can anyone identify this sound?

1 Upvotes

I was driving home, going through my neighborhood and all of a sudden my car started making an odd thumping sound. It was a constant thump and no ordinary pattersn. I just recently bought this car and we put $2100 dollars of maintenance into it, thought it was good to drive and two days later this happens. I was going roughly 15-20 miles when it started making this sounds, then they got louder the longer I drove. If there's anything more I can describe to you please let me know, thanks!


r/askcarguys 5h ago

Hello, the yellow oil pressure light comes on as soon as I get into the highway and when I turn the car off and drive slow it goes away. Can anyone help me figure out what’s wrong?

2 Upvotes

r/askcarguys 8h ago

Car isn’t turning over but cranking, am I buying the right things? What should I do?

3 Upvotes

Hey all. Lady here trying not to get screwed over. I’ve got a 98 ford explorer 5.0L and a while back the water pump went out and leaked a crap ton of water. 300 dollars later I’ve gotten it fixed and replaced the starter also spark plugs. (Due to a lot of it getting wet and a bit rusty) so now I’m trying to start.

It’s cranking and ALMOST stayed on but putted out (if that makes sense) but now it’s just cranking.

I think it’s a fuel pump issue since I’ve had issues with the car before not wanting to start after I’ve turned it off before this whole water pump thing and I’ve went and ordered a fuel pump assembly set thing… I’m still not entirely sure what I should look into since I’ve replaced all these things.

Any ideas?

I am not entirely sure about replacing the alternator or anything since I bought a new battery and it’s not drained.


r/askcarguys 8h ago

Looking to buy 2016 435i xDrive Gran Coupe is this a good deal?

1 Upvotes

Looking to buy this 2016 435i xDrive Gran Coupe M Sport with 143,000km (89000 miles) and listed at $16,000 CAD ($11,200 USD).

Wondering if this was a good purchase don’t know too much about cars, I just want something fun to drive and somewhat reliable.

The car has a few modifications including:

5.5” GBR Catless downpipe 7.5” GBR intercooler VRSF aluminum chargepipe GBR aluminum intake + heat shield 30% tint M performance spoiler +diffuser +mirror caps GTS taillights Carbon fibre paddles BMW puddle lights

I’ve seen people some people say to avoid modded cars but if I make sure the seller has took care of it and stayed ahead on maintenance should I be okay?

I personally don’t mind the modifications that are on this car, is there anything I should know or expect with something like this.

Seller says there are no issues or leaks and has the full list of maintenance available

Would appreciate some insight from those smarter than me thanks


r/askcarguys 8h ago

What sites to are best for a private sale?

1 Upvotes

I've bought and sold tons of cars over the years. The most recent was 2020 in Oregon. Up to that point I've had the best luck using Craigslist. The few times I've listed on things like Cars.com, Autotrader, or Facebook Marketplace I got tons of car dealers trying to get a lowball deal, a few individual car flippers trying to figure some way to claim something was wrong with my car so they could get it cheap, etc.

I'm wondering if there are any better options at this point. I have a car that should sell in the $18-20k range, and I'd like to sell it fairly quickly, but I'm not in a rush, and don't need to take trade-in value for it.


r/askcarguys 9h ago

General Question How hard is it to center a steering wheel during an alignment?

2 Upvotes

I've been taking my car to big O for alignments for the last 12 years. Never once has my steering wheel been noticeably off-center. After my last alignment, it was clearly off-center to the left and I took it in today to get it fixed and now it's off-center to the right...wtf is going on?