Can an engine be overcooled ?

what is the best operating temperature for a beetle engine ?
:bounce

First question is easy - yes!. If you over cool an engine you wont get the impurities out of the oil. Condensation (water) can get in there and needs to be takem out.

"what is the best operating temperature for a beetle engine ?" - ohhh, ya shouldnt have asked that one

But you gotta ask it to get an answer. Now ot depends - you have a baja - right?
You will run cooler than a full bodied car.
"I" like mine to get to at least 90 degrees C. On the freeway cruising at 110 - 120 km/hr (what no not 120.....i mean NO MORE than 110. ) i like it to sit at say ...... 110 C may be a little more if it is a hot day. If it ids a 35C day .... i wont take it to those speeds.

I have a dipstick temp sender in the Dog-O-War and mostly it runs at about 70-85 degrees. On hot days of 35c+ it may reach 100c accelerating and then go down to 90c once motivated. I have found the temp in my Baja is directly related to oil level and of course engine load.

Coming from Newcastle to Dubbo I left on half a sump and arrived on a third of a sump. As the hills ot steeper and the sump got lower the temp became higher with each hill that required third and sometimes second. Coasting down the other side provided some relief from the 125c maximum the full laden 1300tp reached at one stage of the trip and I'd say this was because the sum was low, the road temp was hot (35c) and the hill was long. Mostly the Dog would sit at 100 which is usually quite hot for it anyhow.

I would really like to install head temps but this I'm told is a scary prospect because the oil temps are usually and average reading where as head temps can quite often be seen above the 400c+ mark.

I don't know if you can overcool a VW engine but the advice I've got in the past is that it's good that they do get over the 100c mark for extended periods to burn off any moisture. As a baja I tend not to worry too much about the temps until I get to the 115 marks as that is where most kombis tend to run apparently. I have read that they can top the 135 mark when pushing strong winds on a hot day.

Hope this helps some - Basically a re read of a recent discussion a couple of months ago - have a look back through some of the older posts a few pages back.

Beautiful, i will have to get everythign sorted properly this time as she used to run not hotter than 75C before the rebuild

thanks guys

Every VW engine is "overcooled" at the point of starting up, and if you don't get it up to a decent operating temperature, then it remains overcooled.

So short trips will result in the engine running cool for a lot of it's life.

Running cold reduces engine life a LOT.

Removing the thermostat and cooling flaps results in an engine being very slow to warm up and also results in the cylinders being overcooled and the heads being undercooled (the cooling flaps control and AMOUNT of cooling air on a cold engine and the DIRECTION of the cooling air on a hot engine).

Placing an engine in an exposed place on a car (open frame buggy etc) can result in overcooling too - the cooling fan EXPECTS some resistance to sucking the air in through the grills at the back, into an enclosed engine compartment. Without that slight inlet resistance, it's possible to get too much cooling air, especially on a cold day.

So what's a good temperature for a VW engine?

Well - it's going to vary more than a water cooled car because there is no large bank of "heat inertia" like the water cooled cars have (a radiator full of water). Water cooled cars usually run with water temperatures of about 110c (the anti-freeze and sealed radiator allows the water to exceed the boiling point of pure water at atomospheric pressures.

So there is no one temperature which is best for the aircooled VW, but a range of temperatures.

For the oil, between 100c (212f) and 130c (265f) is good. At 100c the oil will start to boil off any water condensation which has occured overnight, helping to keep the oil clean.

Above about 130c the oil is getting a REAL workout, but this temp is fairly common in the heavy-bodied bus, so it has to be considered still in the "normal" range. As a comparison, the V8 touring cars consider their oil temps as "too high" above about 140c.

Then there is the cylinder head temperature (CHT) to consider. Remember that there is no heat mass of water to keep the head temps down, so they WILL run hotter than their water cooled cousins.

The exhaust valve is the hottest running component in the VW engine - it runs red hot when the engine is working hard (up to about 800c). It gets it's cooling from the short periods it sits on the valve seat between strokes, then it gets bathed in a rush of hot exhaust gases again as it opens. It transfers it's heat directly to the heads, so if the heads are running too hot, the exhaust valve life is much reduced.

The accepted CHT for the VW engine is up to about 205c (400f). This keeps the exhaust valve temps within reasonable limits and is also well below the point at which the aluninium in the heads starts to "crystalise" - which happen just before aluminium starts to melt.

These figures are also used by the home-built aircraft community when using VW engines in small aircraft.

Why both oil and CHT? Well, with a poorly designed cooling system for the heads and cylinders, but a parger oil cooler, you could think the engine was happy and then wonder why it breaks exhaust valves. Or you could have poor oil cooling and an abundance of cooling for the cylinders/heads, and be constantly worried about running hot when most of the engine is actually running cooler than it should.

But in a car, having an oil temp guage is probably enough to give a fair indication fo the engine temps, since the shroud is designed to balance the airflow to the cooler and the heads/cylinders.

Hope that helps.

The engine was also designed to run its best at the operating temp chosen by VW. A lot of time,money and effort went into designing the stock cooling system. Also you will use more fuel if the engine doesn't get up to operating temp.

also when u are below operating temperature none of the clearances are right.

my beetle will get about 70 C with an ambient air temp of about 24 C, and will hit 80+ on a hotter day.

My baja would run on 80degC most of the time. The sender was the sump plug. Run a little hotter on the really hot days. Also when i was thrashing the crap out of it in the dunes. It was a stock 1600 Dual Port with a shagged carbie.

Hopes this helps

Joel

hey Adam go for the dipstick sender ( its made by VDO) because its more accurate and cant get knocked off like the sump plug sender.
as for the engine temp debate, we all measure engine oil temp but really when you think about it what we need to measure and what tends to fail first is the heads. As long as oil temp is kept below 110 degrees then the oil is fine as we change it quite reguarly.
vw made cooling tinware for standard engines, so if a standard engine is used as well as correct tinware then we should have no problems.
but as for hi-po motors this then causes problems.
so we then add larger oil coolers, but what about head temp?
does anyone here measure head temp in their car?

Just put in a cylinder head temp gauge on the weekend. I can't tell you anything about the head temps b/c I haven't driven it since.

I had to lengthen the cable to install the gauge in my kombi. Many people have said this is a bad idea but I thought it was better than mounting the gauge in the floor! Also, for the most part you want to use the gauge to identify normal operating temps so you know when something goes wrong. For this purpose any error introduced by lengthening the cable is irrelevant (as long as it's consistent).

Mine is a VDO Gauge, and sender but yeah the wire gets knocked off all the time. I overheated my engine once in the dunes, because wire came off.