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VWDoc
VWDoc, Independent VW Shop owner
Category: VW
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Experience:  20 years of experience working with VW's. Independent European shop owner and technician.
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Volkswagen New beetle: My car has a temperature light that

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My car has a temperature light that keeps flashing and when the check engine light also starts flashing, the car slows down to 20 miles an hour and won't go faster no matter what (even though the engine can rev up to 3000 RPMs). My mechanic thinks that it is an oxygen sensor or temperature sensor problem, but I had the temperature sensor replaced a couple of years ago and the flashing should indicate an electrical problem. Do you have any ideas?

VWDoc :

Hello, I'm Jason. I will do my best to answer your question quickly and accurately using the information you have provided.

VWDoc :

This sounds like a pretty significant problem, and one that suggests to me that driving the car any further would be a bad idea

VWDoc :

I'll hold for a bit in live chat to see if you can join

VWDoc :

Still holding, but let me ask a few questions first

VWDoc :

I assume this is a 2.0 gas rather than a 1.9 diesel

VWDoc :

Knowing what the fault codes are would be extremely helpful on this one

VWDoc :

and how many miles are on it

Customer: It's not a diesel it has 95000 miles
VWDoc :

Ok, so how long has this been going on, and what are the fault codes?

Customer: I don't know the codes; the mechanic had trouble getting any.
VWDoc :

Ok, can I make the assumption that your mechanic is more of a general type, rather than someone who knows VW well?

VWDoc :

the code retrieval process is a pretty straight forward one

Customer: Going on for several weeks. Began having intermittent hesitation problems about 6 months ago
VWDoc :

Ok, so I can make some general comments and suggestions here, but data is paramount

VWDoc :

this is so I don't suggest throwing the kitchen sink at a problem, which would cost a lot of money

VWDoc :

not to say that this would be a cheap fix, but again, I can only go on my own experience with these cars

Customer: It's hard to give details because it happens intermittently with no consistency sometimes it happens when it's cool sometimes it happens when it's hot
VWDoc :

Do you happen to know why the trouble retrieving fault codes? Any generic parts store reader should do the job fine

Customer: There are no codes to read apparently
VWDoc :

If the engine light is on or flashing, the ECU will store those codes indefinitely, which is why I was inquiring about the mechanic

VWDoc :

even if the engine light turns off on its own

VWDoc :

now, if the engine light flashes, this means an ignition misfire, which also means that raw fuel is being dumped into your exhaust system, which can potentially damage your catalytic converter

Customer: The engine light is on all the time. It only flashes when the problem happens
VWDoc :

If you don't mind me being direct, your mechanic is not being truthful with you, regarding fault codes

Customer: I want you to tell me the truth! Do you know what it could be?
VWDoc :

Ok, let me suggest a few things first...

VWDoc :

1) find a shop in your area who knows VW.

VWDoc :

but I'm not saying that as a cop-out, since I do have a couple of ideas here

VWDoc :

save this link to find a good VW shop

VWDoc :

now

2) the flashing check engine light, and loss of power is quite possibly the central ignition coil

VWDoc :

they develop cracks over time, and instead of the spark going to the plugs, it escapes to ground

VWDoc :

does this issue happen more when it's damp/wet out?

Customer: I haven't noticed that
VWDoc :

ok, because that would contribute to my theory about the coil. Cracked coils act up more when moist

VWDoc :

now, let's take about the flashing temp light. How long have you had this car, and when was your last timing belt/water pump/thermostat replacement?

Customer: I bought the car1999 and I don't think I ever have that replaced
Customer: I bought the car new in 1999
VWDoc :

Ok, so my next thought is that the reason for the flashing temp light is because of a coolant flow problem, likely due to a failed water pump impeller.

VWDoc :

The stock impellers are plastic and crack over time

VWDoc :

Let me show you pictures to explain

Customer: My sense of smell is poor but I can smell coolant sometimes
Customer: So I guess you are on the right track
VWDoc :

ok, one moment, phone call

VWDoc :

Ok, let me know when you can see this pic

Full Size Image

Customer: I can see it
VWDoc :

Ok, obviously, this is a damaged impeller. At worst, it completely breaks apart, and does not circulate coolant at all

VWDoc :

So, in sum, I think we've possibly got 2 separate problems....

VWDoc :

however, if the car get very hot, it could cause the power loss as you describe

VWDoc :

which is why I suggest not driving it until both issues are diagnosed properly

Customer: Ok
VWDoc :

you don't want to deal with a cylinder head gasket replacement also

Customer: Do you know about what this would cost to repair?
VWDoc :

Well, if my assumptions are correct, a coil costs about $225 and takes an hour to replace

VWDoc :

a full timing belt/water pump/thermostat replacement is about $800 at a good independent shop

Customer: Ouch. And both are necessary to fix ASAP?
VWDoc :

again, these are just assumptions based on your description of the symptoms, rather than hard data

VWDoc :

However, it's very bad to drive a car with 1) a misfire and 2) cooling system problems

VWDoc :

if left unchecked, the repairs will outweigh the value of the car

Customer: Ok thx. Anything else?
VWDoc :

not that I can offer right now.

VWDoc :

But more than happy to help in the future, once you have more information, or have other questions about your car

VWDoc :

I'm quite familiar with them

VWDoc :

this is my direct link

Customer: Will you email me a copy of this conversation?
VWDoc :

after rating, you will get a link in your email to reference

VWDoc :

I'm not allowed to email customers directly

VWDoc :

but the system does that

VWDoc and other VW Specialists are ready to help you

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