Cooling issue on NA diesel

[Hiho]

Hello everyone,

I have a low miles 1.5D NA motor that seems to have trouble keeping cool. I'll describe the symptoms and would like to know what to check next.

First of all, the radiator fan didnt come on, so i added a relay and switch. I also replaced the thermo switch twice and still it needs manual intervention. With the fan on the temp will be just above the thin white dash (early mk 1 cluster) while stationary and idling. It goes up a bit when driven gently.

When driven fast, or when driving at over 80km/hr the needle moves to roughly half way between the thin white dash and the orange dash. This is with the thermo fan on. If i switch the fan off, even at high speeds, the temp goes up higher!

This is all with a 71 degrees C thermostat. If i use a 80 degrees C thermostat the temps registered are higher.

I have swapped the water pump, thermostat, radiator, injectors, fuel filter and checked the timing. The injectors seemed to make a slight difference to temp and idle smoothness.

When the motor is warmed up to operating temperature, the top radiator hose is hot and the bottom radiator hose is cool. Is this because the radiator is blocked or because its doing its job?

Please help!

Matt

[ilikevwdiesel]

first thing I would do is remove the thermostat. Coolant leaves the engine via the lower hose. If the lower hose never gets hot the thermostat isn't opening or something is blocking it. Of course you could have a rad that's completely blocked but that's unlikely. Pull the thermostat out and run it without it, see what diff that makes. If the car has the coolant bottle on the strut tower make sure that there's a STEADY stream of coolant coming into the top of the bottle from the radiator bleed line. If it's burping air all the time the head gasket is probably leaking, which will cause the cooling system to air bind and overheat the engine.

[Hiho]

I think that the coolant moves upwards inside the motor and downwards inside the radiator. I am reluctant to remove the thermostat entirely, The 80C thermostat is brand new. Is it possible to install them the wrong way around?

Another thing, having the heater on makes a difference! Is this normal?

[lord_verminaard]

It's pretty much impossible to install the thermostat backwards, the poppet will not clear the lower water neck on the housing.  Sounds to me like you have a radiator that is clogged.  Both hoses should be warm after the temps come up.  Run some radiator cleaner through it, then flush and re-fill.  It might work.

Brendan

[dyoungen]

I'm not that familiar with the VW cooling system but with my F250 Diesel the coolant gets up to temp and goes into the top of the radiator via the top radiator hose and as it cools goes down thru the radiator finally going back to the engine thru the bottom hose after it has cooled.

[ilikevwdiesel]

You are correct coolant enters the engine from the rad at the thermostat housing sorry.

[92EcoDiesel Jetta]

Did you test the new thermostat before installation? I have read accounts of brand new thermostats that are  bad right out of the box. It's rare but it does happen.

[Hiho]

Thanks everyone for your advice, I just swapped the radiator and discovered that the car has been running with a petrol radiator (which is thinner). I also replaced the thermostat. Lets see how she goes now!

[Hiho]

Shes still running hot, with the temperature gauge rising on long hills and when cruising at 110km/h. Is this normal? I have checked all of the cooling system and it all appears to be in order. Could this be an injector pump issue? THe car also has a rough idle.

[maxfax]

Will it run warmer at low speeds or idling..  It isn;t abnormal for them to run a bit warmer when worked hard..   110km/h is a tad under 70mph if I converded correctly...  Does the engine seem to be revving signifigantly at that speed?

Has the temp gauge hit the red at all since you replaced the rad and t-stat??   I think the first thing in order would be to find out exactly how hot it's getting and thus see if it is really overheating or if it's just the gauge..  Either one of those nifty infra-red temp guns or an aftermarket temp gauge would be the ticket here..   Some have even simply dropped a thermometer in the expansion tank, but you probably don;t want to open that when it's good and warmed up...

Does the cooling system build pressure rather quickley, say within a minute of starting the engine cold??? Any traces of oil in the coolant??   And last question I'll blast you with, does the heat work???

[rodpaslow]

With this being a Mk1 with the shorter deisel rad I have a couple comments -  My 1.6 na in a Mk2 body with the longer rad (usually a car with air used these rads) will be slightly over 1/2 way on the gauge.  When I push it hard 75 mph or better it will be up to 3/4 or better on the gauge.  2. These gauges are not very accurate as my gas car at 180° on a aftermarket gauge is barely 1/4 way showing on the gauge.  I don't trust the vw gauges.  If you push the car hard the temp will climb.  I find after a while it will drop back depending on other things like outside air temp, wind etc.

[rabbitman]

I wonder if the water pump isn't pumping hard enough?? And is letting the coolant sit in the rad too long without pushing it into the engine fast enough?

If you can warm the engine up and have the top hose hot and bottom hose cold then it should NOT be overheating since the cold water in the lower hose is what's going into the engine.

How fast does the antifreeze shoot into the top of the coolant tank?

[Familydiesel]

I would be interested to hear how you repond to maxfax's last question about early pressure in your filler tank.  If so, you could have a head gasket leak that is both pressuring the system and will overheat your car.  We had a Rabbit do this with a recently rebuilt head, but the bolts were not retorqued like they were supposed to be at start-up and 1000 miles.  In any case, be suspicious of any early pressure and or seeming boiling while the engine is still cool or just started.  As stated by another, oil in the water is a clear indication of a head gasket problem, but you can still have a head gasket problem with more pressure due to a little leak-by from a cylinder.

[dangerous_D]

Have you checked the temp gauge sender?  If your thermostat and thermoswitch and water pump are ok and you don't have any blockage in the system there's not much else it could be.

[rabbitman]

Has the temp gauge hit the red at all since you replaced the rad and t-stat??   I think the first thing in order would be to find out exactly how hot it's getting and thus see if it is really overheating or if it's just the gauge..  Either one of those nifty infra-red temp guns or an aftermarket temp gauge would be the ticket here..   Some have even simply dropped a thermometer in the expansion tank, but you probably don;t want to open that when it's good and warmed up...

   And last question I'll blast you with, does the heat work???

A candy thermometer works good to drop in the tank, hold it right were the jet of coolant will hit it.

How long can you hang onto the upper rad hose?