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General Information => Troubleshooting => Topic started by: Rising on November 05, 2012, 03:58:53 pm

Title: Thermostat or water pump?
Post by: Rising on November 05, 2012, 03:58:53 pm
My diesel was running fine yesterday. This morning I went out for a quick ride (I'm sort of obsessed right now ) and I noticed my temp gauge starting to rise maybe 5 minutes in (around 2 clicks from the red clicks but it usually doesn't run that hot). I pulled over and turned the car off and went around to check things. Plenty of coolant and still have an accessory belt. So I waited a few minutes till the gauge dropped a bit and drove it home ( I was less than a half a mile).

So anyway at home I let it cool for a couple hours while I worked on my brakes and then checked some more stuff. It appears that in the coolant bottle there is a stream of air coming out but no water... so I'm guessing the water pump isn't functioning correctly or maybe its an air bubble or the thermostat is stuck. Any ideas?

I really don't want to go through any more problems... I think my wife will kill me if this car takes anymore of our money. . . Haha.
Title: Re: Thermostat or water pump?
Post by: 8v-of-fury on November 05, 2012, 04:33:45 pm
Well if it were absolutely fine yesterday, but today presents these problems..

I just replaced the water pump on my 88 1.6 TD and the flow in to the reservoir via the small tube from the upper radiator is very weak, but I have put nearly 3500 km since the water pump with no coolant issues. So I am not sure it is entirely related to a weak water pump.

An air bubble seems unlikely as well. Are both the top and bottom hoses attached to the radiator getting hot to the touch?
Title: Re: Re: Thermostat or water pump?
Post by: Rising on November 05, 2012, 04:47:14 pm
The top one definitely was. I don't recall if the bottom one was 100%. I could go test it. . . So what does cause the flow back into the bottle?

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Title: Re: Thermostat or water pump?
Post by: 8v-of-fury on November 05, 2012, 04:56:15 pm
Well it would be circulating coolant that would allow the coolant to flow to the bottle from the upper radiator.

The coolant flows from the pump up through the engine and out the two head ports. From there it freely and always flows through the heater core (unless it is an mk1 and it has the coolant valve under the hood in the heater core supply line). The front port goes out to the rad, but only flows through the rad if the thermo is open. Meaning until it opens the bottom hose should remain nearly stone cold.

There is a bypass that hugs the block nearly straight down from the front port and this should always have a free flowing path down through the pump and back in to the engine.
Title: Re: Thermostat or water pump?
Post by: libbydiesel on November 05, 2012, 05:15:17 pm
There is a restrictor with a very small orifice in the hose to the coolant bottle.  I once had a small piece of crud plug that hole and had all sorts of weird coolant temperature behavior before figuring that one out (that was back before internet forums...).  I actually added a clear fuel filter into that coolant line prior to that orifice and was surprised at how many little pieces of crud that filter caught. 
Title: Re: Re: Thermostat or water pump?
Post by: Rising on November 05, 2012, 06:00:31 pm
The hose that squirts water in at the top or the hose that runs to the block from the bottom of the coolant bottle?

I'll check the bottom rad hose for warmth tomorrow. If it is warm that means water is circulating through the engine and water pump so what could be the issue then?

I guess after that a coolant flush might be good even though its all brand new. . . And its a mk1 so it has that little bypass doohickey.

Another note is the fan doesn't seem to be kicking on anymore even though I caught it running the other day. (My car never seems to warm up that much ) but I feel like it should turn on before 2 clicks off hot but that should not effect my cooling problems when moving... 

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Title: Re: Thermostat or water pump?
Post by: R.O.R-2.0 on November 05, 2012, 06:02:05 pm
Quote from: libbydiesel on November 05, 2012, 05:15:17 pm
There is a restrictor with a very small orifice in the hose to the coolant bottle.  I once had a small piece of crud plug that hole and had all sorts of weird coolant temperature behavior before figuring that one out (that was back before internet forums...).  I actually added a clear fuel filter into that coolant line prior to that orifice and was surprised at how many little pieces of crud that filter caught. 

99% of VWs have 1/4" fuel line for the coolant return hose, no restrictor in the line..
Title: Re: Thermostat or water pump?
Post by: libbydiesel on November 05, 2012, 06:06:06 pm
I probably should have said that the stock hose has a restrictor in it.  If someone changed the hose and didn't move the restrictor to the new hose then it wouldn't...  :P  IMO, it should have the restrictor because if it doesn't, then there is a decent stream there at higher rpms that always bypasses the radiator.
Title: Re: Thermostat or water pump?
Post by: TylerDurden on November 05, 2012, 07:10:52 pm
I chased this question around a fair bit earlier this fall. 

Eventually I decided that the only way to be certain the WP impeller is securely attached to the shaft is to hold the impeller with a screwdriver while trying to turn the hub. Even if there is flow in the bleed line or heater hoses, it is hard to know if the impeller won't slip at high rpm and temperature, without checking it by hand.

Of course, if you test the impeller, you might as well test the t-stat too.

If both parts pass, the picture gets more complicated.
Title: Re: Thermostat or water pump?
Post by: ToddA1 on November 07, 2012, 04:04:24 pm
I had the above issue 2 summers ago with a fairly new pump. 

At low RPMs, the impeller would be fine and cool sufficiently.  On the highway, the impeller would slip, and run hot.  This was on a Bosch pump with a plastic impeller.

-Todd
Title: Re: Re: Thermostat or water pump?
Post by: Rising on November 07, 2012, 05:05:43 pm
Pulled the thermostat and checked the pump today. . . Thermostat wasn't opening till like 200 degrees and only partially. Tested another I had around an it was fully opened by 178 ish. That's probably my problem. The water pump passed the screwdriver stopping the pulley test. Still can't get the thermostat housing to seal properly though: /

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Title: Re: Thermostat or water pump?
Post by: 745 turbogreasel on November 07, 2012, 07:27:22 pm
If an old gasket is still up in the water outlet, it will leak
Title: Re: Re: Thermostat or water pump?
Post by: Rising on November 07, 2012, 09:31:16 pm
Yeah I tried to use the new gasket I just put in my old engine like a few months ago. Stupid. Ill be picking up a new one of those and a couple replacement bolts for these old rusty ones tomorrow. Thanks for the input everyone!

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Title: Re: Thermostat or water pump?
Post by: TylerDurden on November 08, 2012, 06:20:13 am
The plastic t-stat housings warp in very short time. A new o-ring will still leak if the housing is warped.
Title: Re: Re: Thermostat or water pump?
Post by: Rising on November 08, 2012, 10:09:53 am
I have an early metal thermostat housing... should I put that on when I replace it?

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Title: Re: Thermostat or water pump?
Post by: TylerDurden on November 08, 2012, 10:46:01 am
The metal is better, as it won't warp.

NLA :(
Title: Re: Re: Thermostat or water pump?
Post by: Rising on November 12, 2012, 04:53:51 pm
Okay I changed out the water pump and thermostat with new units. The car still seems to be running warm. Like around 3 bars from the red is normal while cruising. But sometimes it starts creeping towards two bars from red. That seems hotter than normal and its pretty cool outside. Not flogging it just cruising at 55.
 
Fan seems to kick on okay but not till up there that hot. Is this too hot or normal? What else could come into play here?

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Title: Re: Thermostat or water pump?
Post by: 8v-of-fury on November 12, 2012, 05:18:40 pm
Get a stand alone temperature gauge, the stock in dash unit cannot be trusted.. it is old as s*** and didn't work that well new.

Without a real gauge you have absolutely no idea what is going on in there.
Title: Re: Thermostat or water pump?
Post by: Rising on January 03, 2013, 12:36:44 pm
Okay I picked up a mechanical water temp gauge. Where is the old sender for the dash gauge? I can't find it in the bentley. which is frustrating since i know it's in there somewhere. What threads are used on it? 1/8" npt? I have a few different adapters. But anyway is that where i should put the probe or is there a specific place i should put the probe? Is it better to read in one place or another? And once i get it up and running i shouldn't see anything higher than oh say... 180-190 correct? And I guess that would depend on where i put the probe right?
Title: Re: Thermostat or water pump?
Post by: TylerDurden on January 03, 2013, 12:41:22 pm
Usually the coolant temp senders are on the water outlets. IIRC, the one for the gauge is on the outlet facing the radiator.
Title: Re: Thermostat or water pump?
Post by: 8v-of-fury on January 03, 2013, 04:22:08 pm
Quote from: Rising
And once i get it up and running i shouldn't see anything higher than oh say... 180-190 correct? And I guess that would depend on where i put the probe right?

I have seen as high as 200 cruising sometimes, if its a grade.. and 220 if I am pushing it.
Title: Re: Re: Thermostat or water pump?
Post by: Rising on January 03, 2013, 07:43:52 pm
Is yours on the water outlet coming out of the head? I would assume so based on that high of temperature. Good to know what to look for. I'll check my gauge inside for accuracy before I install tomorrow.

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Title: Re: Thermostat or water pump?
Post by: 8v-of-fury on January 04, 2013, 09:19:11 am
Yes in the bottom of the front neck that goes to the rad. Hottest spot for coolant to be read.

Title: Re: Thermostat or water pump?
Post by: ORCoaster on January 04, 2013, 08:18:51 pm
I check water temp gauges by boiling water and letting it roll for a bit.  212 degrees F.  Generally between the 200 and 225 lines on the gauge.  DAS
Title: Re: Thermostat or water pump?
Post by: Rising on January 05, 2013, 08:51:48 am
Quote from: ORCoaster on January 04, 2013, 08:18:51 pm
I check water temp gauges by boiling water and letting it roll for a bit.  212 degrees F.  Generally between the 200 and 225 lines on the gauge.  DAS
perfect! that's about the only constant i could trust i suppose. I'll do so immediately. i went with a cheap mechanical gauge. So i definitely want to know where it is reading.

Quote from: 8v-of-fury on January 04, 2013, 09:19:11 am
Yes in the bottom of the front neck that goes to the rad. Hottest spot for coolant to be read.

Okay so i have an mk1. Actually it's an mk2 engine in a mk1. But i still have my metal coolant neck coming off the side of the engine where there are two sensors. I have the plastic necks from the mk2 as well but I have heard it's best to keep the metal. Now what i'm confused about is why there are 2 different sensors on the neck. One for the coolant temp gauge and one for what? My fan temp switch is in the radiator so what does this other mystery plug do?!

However I'm not sure my temperature sender will fit there as it's rather large and i don't think it can be adapted as small as necessary. however the mk2 plastic neck seems to have a large sensor hole, however it isn't threaded so i may have to potential jb weld a fitting in or some other nonsense. I didn't think this would be this complicated :/
Title: Re: Thermostat or water pump?
Post by: ORCoaster on January 05, 2013, 09:49:25 am
Now what i'm confused about is why there are 2 different sensors on the neck. One for the coolant temp gauge and one for what? My fan temp switch is in the radiator so what does this other mystery plug do?!

Coolant or temp sender for one plug the other for GP sensor.  If temp is cold you get GP's if already warm not needed.  

I think they are both the same thread size.  
Title: Re: Thermostat or water pump?
Post by: smutts on January 05, 2013, 10:16:20 am
On the later mk2 diesels, these two temperature senders are the same, so if you have weirdness with either the temp gauge or glowplugs, swap the plugs around. If one of the two senders is duff, the weirdness will have swapped too. Fortunately I do not write technical manuals. ;)
The senders are not that reliable. :(
Title: Re: Thermostat or water pump?
Post by: nwcali6 on January 05, 2013, 04:49:55 pm
  I installed a new thermostat last week, sadly it wasn't opening until 200 or so and it would run 220+ on the freeway.  Don't always trust even a brand new one, test before install.

  I always thought if you were getting bubbles out of the radiator (in a system that should not have air bubbles from a new fill up) it indicated a head gasket blown?

 
Title: Re: Thermostat or water pump?
Post by: CrazyAndy on January 05, 2013, 05:24:47 pm
NO, keep the metal one as they don't warp or crack like the plastic ones like to do.  I swear, if I see another MK3 ABA with a lower thermostat housing crack . . .  either way, great to see it was the thermostat.  The problem sounded like that from the start.