Temperature fluctuations at highway speeds or after

[oceanair]

Hey -- so if i start her up (1.9) she warms up quickly and normally. Drive around town needle stands at 12 o'clock. Get out on the highway needle fluctates from the top of the 'warmed up' box on the left of the gauge to the same 12 o'clock.

Is my thermostat (which is a year or two old) getting stuck open at those higher rpms? Seems to cool down to the 'box' on the gauge at lighter loads but never into the box, but in the city, no issues and it never goes above pointing up, so it never even gets close to over heating.

I turned on the heat to check and it's hot. I'd prefer not to pull the thermostat if I don't have to on this 1.9, but it was out not too long ago.

I thought it may be the old blue foil messing with the gauge, so i replaced it with the vanagon.com version which works perfectly. Didn't solve this problem, but it did solve the 'tap on the gas at startup' to get the alternator online, so that's a plus!

Thanks -
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84 Vanagon Pop Top Conversion from Tin Top, 1970 Ghia - all sweet rides! Love em!
Previous: Green 72 Tin Top, White 72 Westy, Blue 64 Beetle, Yellow 71 Squareback, 2014 Jetta TDI Wagon - wish I could have them all back!

[E1]

Our van shows normal "all the time" -- except goes cool really fast on downhills. Best guess for our symptoms is thermostat staying open all the time.

If you're does it on flats, too as it sorta sounds like, I'd suspect the temp sensor or wiring straight away though have no personal experience on those causes.
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[Bub]

I had a stuck T-stat a few months back and the temp fluctuated quite a lot- it didn't warm up very well in cold months and the temp would quickly swing between 1/2 and 1/4.
Replaced the T-stat and it works exactly like yours. Warms up GREAT, great heat but the temp still fluctuates noticeably between 1/2 and just below 1/2.
Never EVER even starts to creep past 1/2 even parked with the A/C on. I figure it's all good if it warms up, has heat, and doesn't overheat.
Don't go looking for problems that aren't there!
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[DanHoug]

it sounds like the radiator has deteriorated. your normal temps around town without an engine under load and then going hot at hwy speed suggest the cooling capacity margin is used up. are you hearing the fan cycle on at all? test your fan speeds first before condemming the radiator but at 30+ years old, it is suspect.

replacement radiators are less than $200. fan rad switches ~$25.
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-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[oceanair]

I should probably add that the rad is new and so are all of the hoses, well new 2 years ago.

I think the thermostat is sticking open at higher rpms. I just don't want to mess with that housing and those soft bolt if there is no need.
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84 Vanagon Pop Top Conversion from Tin Top, 1970 Ghia - all sweet rides! Love em!
Previous: Green 72 Tin Top, White 72 Westy, Blue 64 Beetle, Yellow 71 Squareback, 2014 Jetta TDI Wagon - wish I could have them all back!

[E1]

In our case as detailed above, I do think it's an open thermostat over-cooling on downhills. I bought the lowest-temp thermostat that opens quicker in the cold, and in retrospect think I shouldn't have.

That said, ours does not over-cool on the flats, it stays dead-vertical plus/minus an eighth inch. Only fluctuation is up huge hills where it gains a few degrees.

It'll be interesting to hear what others think but in my opinion no thermostat would allow enough flow to over-cool under load on a hot day, rather I think you may be seeing a false reading.
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[oceanair]

Looks like I'm going to have to pull that darn thing.
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84 Vanagon Pop Top Conversion from Tin Top, 1970 Ghia - all sweet rides! Love em!
Previous: Green 72 Tin Top, White 72 Westy, Blue 64 Beetle, Yellow 71 Squareback, 2014 Jetta TDI Wagon - wish I could have them all back!

[E1]

I may have convoluted my own point... I actually don't think it's your thermostat...
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[Wildthings]

When I did my engine swap a couple of years back and installed a new thermostat, the temperature was quite erratic for a half year or so, but eventually calmed down. I am guessing that the new stat was sticking. When checked in boiling water all seemed well.

For E1 Going to a lower temperature thermostat doesn't buy you much maybe an extra minute on a hill climb if your radiator is getting a bit clogged. The engine should last longer and get a bit better gas mileage with the stock thermostat.

[DanHoug]

what bothers me is that the temp is fine around town... thermostats don't care what RPM is. so, given a new rad, i'm going with a fan problem.

i had a brand new Wahler t-stat run very high righ out of the box. but it ran high at idle to hwy speed. swapped it out for a used t-stat and normalcy returned.
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-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[Wildthings]

Unless it is dang hot or you are pulling a long grade the fan isn't even going to come on.

[oceanair]

Yeah -- the needle never goes over half so the fan does not come on. Fluctuation is half down to a third from the right of the 'box' on the gauge to half way. It can move quickly as well.

I think the gauge is accurate because when i suddenly put the heat on, the needle drops a few widths as it should.

I think I'm going to have to bite the bullet and pull the T-stat. I'm just not wanting to get into it on the 1.9 if I don't have to...
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84 Vanagon Pop Top Conversion from Tin Top, 1970 Ghia - all sweet rides! Love em!
Previous: Green 72 Tin Top, White 72 Westy, Blue 64 Beetle, Yellow 71 Squareback, 2014 Jetta TDI Wagon - wish I could have them all back!

[Gizmoman]

[oceanair]

I appreciate the interest everyone. I'll try to get a video. I've had this van for a bunch of years and the needle moving around is new.

It never moved much unless I'm in traffic and then the fan kicks in. But the needle moving from straight up to the left 'warm up' box line in a 10 seconds is new, it never moved more than a width or two after warm up.

I'm going to get at the T-Stat and see what happens -- new one and see what happens.
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84 Vanagon Pop Top Conversion from Tin Top, 1970 Ghia - all sweet rides! Love em!
Previous: Green 72 Tin Top, White 72 Westy, Blue 64 Beetle, Yellow 71 Squareback, 2014 Jetta TDI Wagon - wish I could have them all back!

[Mellow Yellow 74]

[E1]

Mellow, that's just what I'm thinking.

The point I may have failed to make is even with a wide-open thermostat, on a hot day, the van should still not run cooler than normal, which in my view is 12:00 High. A clog anywhere in the line, whether radiator or hose, is going to err on running hot, not cold.

WildThings, I agree. I bought that thermostat thinking "early cooling must be preferable on a hot day" but think now it's overkill in all ambient temps, except when very cold out and wanting earlier opening and quicker interior heating. I was wrong (bought with the first parts order, supported and perhaps co-misdirected by the vendor) and will install the normal thermostat next time.

Our cooling system works dead perfectly, never even close to getting hot even up huge passes in Death Valley. Maybe an eighth-inch right of straight up max, and we're at GVWR. I don't rev it hard up hills though, either. Its only flaw is over-cooling on long, off-throttle downhills, and I'm dead convinced the thermostat you recommend would/should close off slightly in those conditions to keep coolant temps closer to 12:00 High. As you know, engines don't like running too cold, either.

Thanks for that insight.
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[oceanair]

Seems like the next best move is a new T1 sender. It's cheap and easy.

Any advice on how tight to torque it or anything else? The wiring looks very good, the connector is clean and I replaced the blue foil so it's all fresh. If that doesn't do it, the thermostat will be next.

Thanks --
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84 Vanagon Pop Top Conversion from Tin Top, 1970 Ghia - all sweet rides! Love em!
Previous: Green 72 Tin Top, White 72 Westy, Blue 64 Beetle, Yellow 71 Squareback, 2014 Jetta TDI Wagon - wish I could have them all back!

[E1]

Hope that nails it, Oceanair, I'm of a "start easiest and cheapest and then spend more money and time" kinda thinker. I remember when a mechanic installed the wrong front bearings on our early '84, and there were all sorts of expensive suggestions because our brakes failed exactly in that bearing change instant. Instead, "I" thankfully -- via Peter at Van Cafe, and Bless That Man in general -- stayed on the simple, and the real fix cost next to nothing as it always seems to for us so far.

Unless someone knows a torque value or it's in the Bentley (coffee's in the way of dragging it out, Wink), I'd just snug it up and add a fair tish more.

I do so on parts easy to access in general, and check for leaks or other bad signs frequently early on, and that's worked for a long time (nothing's ever fallen off, Ha!).

If a comparison were asked, I'd say "spark plug tightness," if that makes sense.
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[tencentlife]

Check the size of the bypass-blocking disc on the end of your thermostat. It should be 33mm +/- 0.5mm diameter. If that disc doesn't cover the bypass port when the t-stat opens, you can get some pretty erratic operation of the cooling system and strange gauge temp readings.

Like most vehicles made since the early 80's, both 1.9 and 2.1 wbx thermostat housings implement a bypass cooling loop for rapid and even warmup. Either type can accept incorrect t-stats that have over-large bypass-blocking discs. In the 2.1, the bypass port is in the bottom of a conical well, so if the disc is too large it will still block the bypass, just at a lower temp, not a big deal. The 1.9 housing, however, has an irregular bump inside the well that juts out such that if the disc is more than about 35-36mm dia., it will be blocked from reaching the bottom of the well and the bypass won't be blocked, even partly. This will upset the intended hot flow pattern, and it's kinda hard to predict exactly what you'd see at the gauge but the cooling efficacy is definitely compromised.
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[oceanair]

Thank you everyone -- I'll switch out the sensor tomorrow -- if that doesn't work, I'll get the T-Stat out and see how it looks and give it some tests and report back.

Much appreciated --
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84 Vanagon Pop Top Conversion from Tin Top, 1970 Ghia - all sweet rides! Love em!
Previous: Green 72 Tin Top, White 72 Westy, Blue 64 Beetle, Yellow 71 Squareback, 2014 Jetta TDI Wagon - wish I could have them all back!