Blink... Blink... Blink...

[BigggWilly]

Goes my coolant light... sometimes... randomly.

Okay, I recently got a 91 Jetta 1.6L NA. I've got this problem with the coolant light. When I start it up in the morning, (completely cold) it starts fine, and the coolant light blinks maybe twice (fine). If I heat it up, and then turn it off, then start it again up to about 2 hours later, about 80% of the time the coolant light blinks for inbetween 10 seconds to 20 minutes.  :?:  :!: . I have absoluetly no idea why this is happening. When I bought the car, the coolant tank was all scummy, and coated with oil. So, I changed the head gasket, and cleaned out the coolant tank, and change the coolant. The flashing subsided for about a week, until the coolant tank go all scummy again (from all the oil scum left in the rest of the system, I assume). Now, the flashing has started again, and seems to be a little bit worse. The car never overheated, it runs between 1/8 to 3/4 on the temp gauge. So does anybody have any idea why this is happening? The coolant level is good at cold temperature, but sometimes If I open the tank when its still warm, the coolant will be to the very top of the coolant tank.

Thanks a bunch,

Will.

Oh yeah, also any ideas to de-scumify the coolant system? I would like to be able to see my coolant level.

[BlackTieTD]

there is a sensor that triggers a warning light if your coolant level is too low.. at least i *think* there is one in your car (my mkIs don't have this... but my mkIIs do.. your's is a mkII).

either your coolant is just a touch low, or more probably, the oily scum is confusing the sensor. flush the coolant system through with a hose for a good 1/2 hour to an hour... thats what i did to the rad and heatercore/lines before we put the new engine in after the old one's HG let go... and the coolant is pretty clean still, that was 5000+km ago.

[fspGTD]

I've tried using prestone coolant flush, but can't say it really did anything.  I heard straight from a very experienced and knowledgeable radiator specialist that the coolant flush things on the market aren't any good, and about the best you can do by yourself to flush the system is just use water.  Remember you've got to get the engine hot before the thermostat opens and lets everything circulate.  But Bentley recommends not draining or adding coolant when the motor is hot (risk of head warpage apparently) so it is time consuming to flush.  The heat does help things get into the coolant though.

What you might consider is taking it to a radiator specialist and having them flush it.  They have products that are more aggressive than what we can buy over the shelves.  This guy was telling me the only problem with those hardcore professional flush treatments is that if any is left behind like in a nook or cranny where it wasn't flushed out, due to high acid or alkaline level it's not a good thing.

When the plastic expansion tanks get old and oil-stained, it seems the plastic gets dyed, about the only way to make them clean is to buy a new one.  Luckily they are cheap - only about $10 ea (for the non-sensor version)

Also FYI: all factory TD's (A1 and up) have the water level sensor in the coolant.  Naturally aspirated A1 diesels don't have the sensor.  I never bothered adding it when I swapped the TD into my Rabbit but when it's working it could be a very useful warly warning in the event of coolant loss, which would show up before the water temp gauge started climbing (which can be too late, IE: the engine could already be critical hot at that point if you've got a catastrophic coolant loss.)

[BlackTieTD]

Also FYI: all factory TD's (A1 and up) have the water level sensor in the coolant.  Naturally aspirated A1 diesels don't have the sensor.  I never bothered adding it when I swapped the TD into my Rabbit but when it's working it could be a very useful warly warning in the event of coolant loss, which would show up before the water temp gauge started climbing (which can be too late, IE: the engine could already be critical hot at that point if you've got a catastrophic coolant loss.)

i'm on it..thanks jake.

[BigggWilly]

Thanks guys for the helpfull hints and the speedy replies! I'll have to try the coolant flush this weekend; I guess I should probably buy all new coolant as well .

This forum is about a 1000 times better than the vortex; at least for diesel info. Seems like there is a lot more knowledge here!

Thanks again!

[type53b_gtd]

The erratic flashing coolant light can be caused by low coolant level, a bad or gummed sensor in the tank (unplug it and short the connectors to verify this) wiring to the control unit or the control unit itself (which on your '91 is in the instrument cluster printed circuit, sorry to say.)  Coolant tanks since '90 all have the level switch integral with the tank, so if yours has gone south you'll have to either replace the resevoir or do without.

I have a '92 Golf that I work on regulary which has  a bad control unit - the driver has been putting up with the very erratic flash for about 18 months now - he seems to be a pretty easy going guy, it would drive me buggy.   On the earlier cars you could unplug the control unit from the relay plate, but of course on the newer ones it means a new printed circuit...

Drew

[BigggWilly]

Thanks guys for your help!

The flashing light isn't completly random, it only happens after the car is warm started, it'll never come on in the middle of a drive. I noticed that it stayed on the longest (about 30 mins) after stopping for a few minutes at a rest stop on the 401.

I'll definetly try jumping the level sensor tonight, hopefully that'll help me zero in on the problem.

Thanks again!