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Author Topic: MK2 overheat / water pump questions  (Read 4321 times)

May 05, 2023, 07:37:05 am

30dodgeboy

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MK2 overheat / water pump questions
« on: May 05, 2023, 07:37:05 am »
Have a 1.6d in a Jetta, and have put about 10k miles on this engine since swapping it in to replace the previous one that was tired and ate a head gasket.  The water pump was on this engine when I got it.

Just recently its been overheating, and the issue seems to be progressively getting more severe. 

I installed a new 180 thermostat, and tested the old one - which seemed to open right at spec.  The coolant flow through the vent line seems good when the coolant is cold.  Since this issue developed, the vent line flow has been dropping off as the coolant temperature climbs.  When the engine is hot (say 180-200) the vent line flow is just dribbling now at idle.  It increases when the engine is revved, but is not what it used to be.  Before this issue the vent line flow was same hot or cold.   I checked the orifice in the vent line and it is perfectly clear.  I suspected then maybe a water pump issue and checked to confirm the impeller is tight on its shaft, and it seems to be.

I was thinking maybe head gasket issue, but the engine cranks evenly, and a nitrile glove on the reservoir doesn't inflate.  Also the vent line flow isn't aerated when the engine temp is climbing past the thermostat opening temp. After refilling the system, and the system has purged the initial air out, the vent line flow is liquid only.

I don't know how to upload pics to this forum, but the pump has a stamped steel impeller that looks just like the images of RockAuto's FVP 1801070.  Same as this link:   https://www.pelicanparts.com/More_Info/1801070.htm?pn=180-1070-INT   The impeller blades all look intact, but don't seem to "seal up" much against the housing like the images of the cast impellers do.  However, the impeller didn't change its shape just recently, and this pump cooled the engine without any issue for 10k miles before this.  Pump bearing is snug and smooth, and seal is holding fine.  Judging by the stainless M6 fasteners, its been replaced.

The heater performance has been erratic as well lately.  Heater core is new and I resealed the doors in the heater box at that same time.  Sure seems like water pump to me.

Anyone have ideas or suggestions??





Reply #1May 05, 2023, 11:09:04 am

Dennis Froelich

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Re: MK2 overheat / water pump questions
« Reply #1 on: May 05, 2023, 11:09:04 am »
What about the housing the water pump bolts to? Did you check to see if the housing got chewed away from the water pump impeller? Just a thought as I have had the same problem with running warmer than it should.
The housing had been screwed up by the impeller.
79 Golf GTD
96 Golf GTD(TDI)

Reply #2May 07, 2023, 09:34:59 pm

fatmobile

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Re: MK2 overheat / water pump questions
« Reply #2 on: May 07, 2023, 09:34:59 pm »
How did you check the orifice in the vent line.
It could be flowing nice, then as it runs a little a chunk is pushed into the restrictor.
I just remove the restrictor.
I know this can cause increased flow into the reservoir, which can splash against the pressure relief valves in the cap and cause them to open.

I've heard of people using a piece to direct the flow downward,
into the reservoir and away from the cap.
Tornado red, '91 Golf 4 door,
with a re-ringed, '84 quantum, turbo diesel, MD block

Reply #3May 07, 2023, 10:59:20 pm

30dodgeboy

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Re: MK2 overheat / water pump questions
« Reply #3 on: May 07, 2023, 10:59:20 pm »
How did you check the orifice in the vent line.
It could be flowing nice, then as it runs a little a chunk is pushed into the restrictor.
I just remove the restrictor.
I know this can cause increased flow into the reservoir, which can splash against the pressure relief valves in the cap and cause them to open.

I've heard of people using a piece to direct the flow downward,
into the reservoir and away from the cap.

Thanks for the input, I appreciate it.

I had the orifice plug up with the previous engine several years back before, so I cut it just upstream of the orifice and then spliced it back together.  This makes it very easy to remove the section that is the last few inches of the vent line containing the orifice to be able to look through it visually as well as remove any debris that may be present. 

I am 100% sure the orifice is clear.  The flow rate is decent when the engine is cold, and drops off when the engine heats up. If the orifice were plugged or partially blocked, the vent flow rate wouldn't be decent again at the next cold start-up.

I only fill the cooling system with a funnel with a fine screen to ensure nothing can plug the vent line orifice or heater core or radiator core.

The vent flow rate seems less than the other two MK2 VWs I happened to be working on today, I believe there is a water pump problem.

I just need to wrap up some axle repairs for a friends car before I can get back on to this one 100%.

Reply #4May 15, 2023, 07:38:10 am

30dodgeboy

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Re: MK2 overheat / water pump questions
« Reply #4 on: May 15, 2023, 07:38:10 am »
What about the housing the water pump bolts to? Did you check to see if the housing got chewed away from the water pump impeller? Just a thought as I have had the same problem with running warmer than it should.
The housing had been screwed up by the impeller.

I have it apart now and can see that the water pump's stamped steel impeller vanes were surprisingly far from the housing.

I have another used pump with a cast impeller and its vanes are substantially closer to the housing, like I would expect.

What I can't understand is why this overheat issue has gotten worse lately as the water pump impeller didn't change...

Reply #5May 15, 2023, 10:42:24 pm

fatmobile

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Re: MK2 overheat / water pump questions
« Reply #5 on: May 15, 2023, 10:42:24 pm »
Did you try removing the restrictor completely?
 I'm thinking there might be a chunk in that thin line.
 One that goes back toward the radiator when it's not running and flows back into action when it's running.

 I've often thought about pressing a cast impeller off the old pump and hot/colding it onto a new pump.
Tornado red, '91 Golf 4 door,
with a re-ringed, '84 quantum, turbo diesel, MD block

 

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