81 Jetta diesel is overheating

[Sivamboy]

I am new to the forum. I have a 81 Jetta diesel, that I have owned and operated. I am having a overheating problem. Gone through the cooling system, replaced thermostat, hoses ok. I drained out coolant and flushed out with water. Might have introduced air not sure. Have run the engine in idle without the temp needle going off center (my normal op temp) but as soon as I rev engine, temp needle goes up fast. One thing I have observed the radiator is not hot to touch, even after two hours of idling the engine and watching temp gauge in normal operating temp. So I suspect radiator failure. One thing that is bugging me is there was no overheating (off center needle) before draining coolant and running water to clean out, so I suspect air pocket. Is that possible. By the way, top hose to radiator is hot, bottom hose is also hot to touch after long idle, but radiator cold to touch. Any suggestion and help is greatly appreciated.
Thanks
Sivam

[Mathius]

I had a 16v passat awhile back, and the same issue as your describing.
First thing to ask is, did you happen to notice any air bubbles or pressure in the system?
I fought with mine for weeks before I realized the head gasket was gone. No coolant in oil, or vice versa. It was just pushing exhaust into the coolant.
Might be worth looking into...

But air can get trapped in there to!
First off (with the motor cold) you can squeeze the hoses to push trapped air out, starting low, and working your way up. Just keep an eye on the reservoir. Most cars aslo have a bleeder cap on them to. It's about an inch around, and should be located on the upper hose somewhere? You can pull it to help you burp the system.
Try to get as much out by hand as you can before running the motor. Theoretically if you get most of the air, it can burp itself of any small pockets.
Hope this helps, and good luck.

[Sivamboy]

Thanks for the reply. On your second part of your response. I am assuming with the reservoir cap open, squeeze the bottom hose and work my way up to upper hose correct? I have also checked the overflow hose from radiator to reservoir for blockage.
On your first part of your response, yes my head gasket was leaking coolant to the outside, not to oil, I have checked the exhaust, no white smoke. So your theory exhaust to coolant is possible. So I am hoping that part is also sealing with treatment. I am running gasket sealer right now, I have observed the coolant external leak slowly sealing up as I idle the engine. So I believe I am solving that problem. I didn't experience overheating (above center temp gauge), before I flushed out engine with water in prep for head gasket seal treatment. Overheating (off center needle) happened before I started the head gasket treatment and continues with the treatment.

[colby]

Sounds like its air bound to me, but I've also seen a faulty radiator cause similar symptoms. I believe I parked mine on a slight uphill incline, and ran it with the cap off and squeezed the upper radiator hose several times to burp the air out of it, then recapped, drove it down the road, brought it back home, did the same thing, and topped off the coolant tank.

[Sivamboy]

Mathius and Colby, you guys are a life saver. I did put the car on a ramp so that the radiator was at the highest point compared to the rest of the cooling system. Then I squeezed the bottom and then followed by top radiator hoses in sequence. The procedure produced burp's in the system, air bubbles in the the reservoir, then the level went down filling the air pocket. I have driven the car about 30 miles, the radiator is getting hot again. I am not totally out of the woods yet, but at least back to square one which is fixing head gasket issue. Keeping my finger crossed. I bought this Jetta when it was new, and I thought I have seen very problem/symptom a few times over after 330K. This one stumped me, thanks to all of you for your collective knowledge and help.

[Mathius]

There might not be a head gasket issue?
A sure sign is pressure building in the cooling system. Mine actually blew hoses off, and would overheat in a matter of minutes.
If you feel air is still trapped, just repeat the process over again. It's a trial, and error thing.. lol

My neighbor did mine in my 91' IDI. But he has the purge vacuum kit to do it all legit like. If you really needed it, I think he got it on ebay for like $50.
Works awesome!!

[Fatmobile]

The engine should easily purge air on it's own.
If it isn't then the small line from you radiator to the resevoir is probably clogged.

Look for flow into the resevoir, from that small hose near the top. No flow means clogged. Spurts of air usually means head gasket.

[Sivamboy]

Thanks for the input, I will check the overflow line.

[greg lousy]

I like blowing through the little hose. You should be able to blow bubbles in the reservoir. If it is clogged it will be in a small pin size restricter hole either in the barb at radiator or in a separate rubber restricter jammed in hose . If its a separate restricter, I take it out and throw it in the garbage

[Fatmobile]

On the MK1 the restriction is usually in the barb coming off the radiator, blowing through the hose and making bubbles in the reservoir won't find this.
On the MK2 the restrictor is inside the small hose, which is built into the radiator hose and can't be blown through.

[Sivamboy]

Thanks! I just changed out the line. I also cleared out the hole going to the reservoir also cleared the inlet to the radiator. I still have the issue of fan not coming on. I have read your post. Changed out radiator temperature sensor, checked the wiring changed out two connectors, one on the radiator temp sensor, the other on the ground from the fan. Just for better connection. I jumpered the fan and got it to run. Checked the fuse. Bentley I have said for 81 Golf diesel there is relay. Mine is German build 81 Jetta, I don't see a relay. Any comments on this?

[TylerDurden]

I'd check the water pump.

• The lower radiator hose should not be warm/hot if water is flowing.
  Lack of flow will prevent air from purging.
  An idling engine will normally cool off (compared to cruising) and low flow will heat up the engine quickly.

I'd check to see if the cabin heater gets hot with the valve open and fan on high, if not the flow might be low.

Those laser temperature gizmos are handy to take readings on engine, hoses and areas of the radiator.

[greg lousy]

On the MK1 the restriction is usually in the barb coming off the radiator, blowing through the hose and making bubbles in the reservoir won't find this.
On the MK2 the restrictor is inside the small hose, which is built into the radiator hose and can't be blown through.

sounds like the hose is clear here, but for the record I'm talking about just taking the small hose off reservoir end and blowing through the radiator and engine, bubbling out the res. I've done it as a quick check with both types of restrictor

[Fatmobile]

Sooo the fan works but won't turn on with the thermoswitch???
I upgrade my cooling fans to the MK2 style where the relay is mounted to the radiator fan shroud.
Power from the battery, through a fuse, goes to the relay and thermoswitch.
The thermoswitch then goes to the trigger on the relay. I also hook a manual dash-mounted switch to the trigger.
Output of the relay goes to the fan.
Relay also needs a ground.

Saves alot of going through the firewall.
And gets you away from the sketchy early jetta fuse box.

[Sivamboy]

I drove over 1,000 mile trip. I took the costal route, US 101, elevation change of 1.5 to 2 K. The temp gauge was slightly off center, I did not hear the fan when I stopped the car on several occasions to check the engine. On return trip, I wired the ground wire from fan directly to ground on battery. On one occasion, I noticed temp gauge go off center, and then drop to normal. Presumably fan might have gone on but no comformation. Just yesterday, hot day after some stop and go, parked car, actually heard and saw the fan go on. I was wondering if parts of the radiator was not getting hot especially around thermal switch thus not triggering the fan. I noticed on 1K trip, checking the temp around, the radiator didn't get too hot. I am thankful that fan came on a relatively hot day.