temperature sensor mystery...

How do you know engine temps are "fine"?

@johnwrightphoto

Who built the car?  

Was it a CMC home built car?  

A factory built VS, Beck, or IM? Or a roller that was completed by someone in their garage?

And as Al asked, how do you know the engine temperature is fine? Did you use an infrared thermometer?

Is it the oil temperature or the cylinder head temperature that has you concerned?

Let's see the rest of the engine bay too.

Where is that mounted --- on a head where the later fuel injection sensor is/was? It's a temp head sensor?  Does the sender match the gauge (check gauge model and its matching sender)?

The picture looks like a pressure sensor for an idiot light. That would only give you an off or on signal not a variable temperature signal. for a temperature gauge you would need a temperature sender, they look different check on Thesamba.com

Hi, John!

OK! A few basics, here....

No, your gauge should not be in the red all the time.  That said, you don't know the true oil temperature unless you measure the oil in the crankcase once the engine is fully warmed up.  For that, you need a dipstick thermometer (and while I own a Fluke Infrared temp probe, I wouldn't use it to accurately test crankcase oil temperature).  Typical VW dipstick thermometers cost around $50 bucks, but you can make do with a candy or sauce thermometer from Bed Bath and Beyond.  Pull out your dipstick and measure the length from the cap that sits on the case tube to the lower end and buy a candy thermometer the same length (an inch or two longer is ok, shorter is not).  Calibrate it in a cup of boiling water for 212°F.  If it's not adjustable, just write down what it reads in boiling water and THAT is 212°  An analog dial is fine - you certainly don't need a digital one unless you want to use it on your grill (wash it first!)

Once you have a long thermometer you can trust, go for a ride on a highway and get it up to 60+ mph for 20-30 minutes and then stop, and immediately test it with your candy thermometer by removing the dipstick and inserting the candy thermometer in its place.  You should be looking for something between 190° - 215°.   Anything over 215° is hot.  Anything over 220° is really hot and if it's over 230° pull over and stop.  I would trust this far more than someone telling me that "it's not hot".

Your sensor, from the photo, is just to the left of the distributor (I can see the distributor clamp bracket in the right background), the same as 99% of the other Speedsters on here and probably 90% of us use just a standard VW oil temp sender, available from NAPA, CIP1, Bug City and a bunch of others, and also available from Vintage Speedsters.  Yours looks just like mine (yours is maybe cleaner).  A sensor for a 1970 1600 sedan should work.

Oil temp sensors fail in three ways:  Either they start reading consistently low or high all the time, or they fully fail (giving no reading at all) or they leak oil.  Yours is not leaking so it's one of the other two.  A fourth possibility is that that sensor is wrong for the gauge, but you haven't yet told us what you have for gauges so I can't tell.  Lots of CMC cars have "Classic" gauges while Vintage Speedsters runs Asian VDO knock-off gauges and Beck and IM are now selling updated real VDO gauges.  All of those may or may not use different temp sensors, I just don't know.

OTOH, a new VW sensor is about $10 bucks and you simply remove the old sensor and install the new one - easy peasy.  Put oil resistant thread sealer on the threads (just a little).  Nothing special is required for the swap.  Go for a ride and see what the new one reads.  

If you have an idiot light sensor in there, the gauge will read low (really low) until it gets up to around 220° or so and then will go from all the way low to pinned on the high side in an instant.

On all of the other questions, we see a lot of homebuilt cars without proper heat shielding installed around the engines and that was one of the questions.  Not having those shields in place lets you look down on the engine bay and see the ground under the engine and that can make your engie run hot.  

Your photo does not show a cylinder head temp (CHT) sensor, so don't worry about that.  

Can you send along a photo of your dash gauge?  That would help a bit.

Good luck fixing this.  It's not too big a deal (I hope) and should be an easy fix.

Gordon

The Speedstah Guy from Massachusetts

Hmmmm I kinda knew i should have posted my question in the 'NEWBIE' section ...

Thank you very much for your responses everyone. Forgive me if my question lacked enough information for a realistic diagnosis. I'm afraid I don't know which engine I have outside of it being a 1600 and I wish my knowledge were such that I could tell you 'where it is mounted' Wolfgang, but I can't

But, I think I can answer the 'how do I know it is fine' queries. With the sensor connected the gauge automatically goes to the red when the car is started and stays there. The gauge has one reading from start up: Red Zone.

This car was a home built project back in 2000. I'm the third owner and the previous owners seem to have nursed her, neglected her, stored her, then sold her. The cycle of neglect and storage has created a car with a genuine patina but she seems a little weary I'm looking forward to making her great.

The history shows a 'new' engine install in 2006 and a rebuild to that engine in 2016 with new barrels, pistons, gaskets and seals and recon carbs.

The engine has done 3000 miles in 10 years.

Gordon, thanks for your in depth answer! Your advice and suggestions are very helpful and show me a way forward. In truth, I genuinely don't think the engine is overheating (Of course I may be wrong) but I will try your candy thermometer test! Add to that I'll get a new oil temp sensor, probably the VW 1600 sedan model as you mentioned. I plan to completely replace the gauges as the current ones are naff! At that point i'll be sure to fit the appropriate sensor to match the gauge. I'll check out the VDO gauges when i get to that part in the upgrades journey.

"...we see a lot of homebuilt cars without proper heat shielding installed around the engines..."

Yup, this one has nothing keeping the exhaust heat from the engine and nothing keeping the engine noise from the cabin. High on that list of 'upgrades' is to fabricate an engine bay with heat shielding

Thanks again for your responses.

John

John, getting tins in that engine bay should be a priority, particularly if you intend to drive it in the heat of the upcoming summer. If you could post pictures of the engine, from several angles and from the bottom, including where that sensor is, I'm pretty sure the guys hers could provide you with a lot of good advice about bringing things up to snuff!

WTTM!

johnwrightphoto posted:

 

...But, I think I can answer the 'how do I know it is fine' queries. With the sensor connected the gauge automatically goes to the red when the car is started and stays there. The gauge has one reading from start up: Red Zone...

 

John, this doesn't sound like enough info to assume all is well.

It just seems to say the gauge and/or sensor aren't working right and nothing they tell you is reliable information.

For starters, try following Gordon's advice, using a simple external thermometer.

Agree that is sender for the oil pressure idiot light.  We normally see a double wire sender for idiot light and oil pressure light plus an oil temp sensor mounted on a brass fitting (they could be located elsewhere). 

Here is how I wired my up recently (using the adapter). Temp pressure and oil temp in the same spot as @WOLFGANG shows above.

It looks like you installed the distributor upside down Brian! Bwwaaaa Haaaaa Haaaaa

No wonder you're having problems with the fuel gauge too!!

Robert M posted:

It looks like you installed the distributor upside down Brian! Bwwaaaa Haaaaa Haaaaa

No wonder you're having problems with the fuel gauge too!!

sherco_chris posted:

The picture looks like a pressure sensor for an idiot light. That would only give you an off or on signal not a variable temperature signal. for a temperature gauge you would need a temperature sender, they look different check on Thesamba.com

I think Chris and Wolfgang have identified the problem.  Can you remove the sensor and post a picture of the portion that threads into the engine?

James

@longfella    what is that round gray thing?

That's the distributor, Mike.  The picture shows the engine inverted on an engine stand.

I see that now. I only saw three posts coming out of the bottom and that prompted my question.

When I bought my buggy the owner said he could not get the oil temperature gauge to work.  The sender was located at the bottom of the sump, in the sump plate.  I really don't like this location and I don't think it gives an accurate reading.

I plan on buying a new sender and locating in up where the oil pressure sender is located.

I plan on buying a VDO multiple adapter

and a new sender

John, you might think about going this route too.

CB sells both: 

http://www.cbperformance.com/S...l+temperature+sender

Michael McKelvey posted:

@longfella    what is that round gray thing?

I thought it was a cow udder!

Just remember, guys, that if you use the VDO dual pole oil pressure sender (for gauge and idiot light) that the dash light may flicker or even come on when the engine is at operating temps and idling, especially if your engine likes to idle a little low. The light comes on when pressure drops below 8-9 lbs (not unusual when an engine is broken in) with the dual pole sender, whereas the stock dash light sender turns the light on only when pressure drops down below 2-3 lbs.

@ALB @WOLFGANG @Ron O @James @*LongFella @Sacto Mitch @Panhandle Bob @Gordon Nichols @sherco_chris

Guys!?

Thank you all so much!

I'm a new speedster owner and a new forum member. I can't believe how you've all rallied with ideas, suggestions, pictures and support.

I wasn't sure i'd even get a response to my little iphone photo from rainy England of a sensor when I didn't even know what it was!

I'm blown away by your support and i will update this post with the resolution of the issue in the hope that it will provide some confirmation for you all who have taken the time to post.

I'll take it off the engine @James and post a pic the connection

Going straight over now to become a supporting member of this forum.

Thank you all for your support and guidance.

John

@James so if anyone is still with me, here attached are some images of that temperature sensor removed from the engine

My gauges look a lot like the green numerics/black background VDO gauges but knowing the car and previous owners standards of work, I very much doubt they are authentic VDO.

Based on this can anyone recommend the definitive sensor to replace this one with?

John

I've never seen gauges with orange needles :/

Maybe an email to one of the gauge rebuild places could shed some light??

I suspect the needles are faded or don't show actual color in photo.  If you pulled one of gauges or could see the back of gauge, it might say made in Brazil (if 10 years old) or Made in China.  I suspect that sender is for low oil pressure light as that is normal place for one.  If so it either reads open when there is oil pressure and closed when there is none (could check using an Ohm meter).  Is there another sender for oil temp somewhere - like oil drain sump?  An oil temp would send different voltage depending on temp.  What make/markings are on that sender? The bezels do have some corrosion on them so they could be 356/912 German gauges. Is your car a Chesil?

John - Visited out your way a long while back when we visited some friends in Chelmsford.  Here in Massachusetts we pronounce our Chelmsford "Chems-fed".  It's near Lowell, Ipswich and Gloucester.

So rather than try to complicate this further, let's find what's driving your temp gauge needle:  Start your engine.  If the gauge goes full right with the key on and engine not running, even better. See the temp gauge go full right, go back to the engine and remove the wire from the sensor you've shown next to the distributor (Be very careful of the spinning fan belt and pulleys). 

If that is the temp sensor the temp gauge should immediately drop to zero (left).  If the gauge doesn't move then that is the oil pressure idiot light sender and  you must look elsewhere on the engine for another sensor, typically on the bottom of the case and either screwed into the drain plug on the very bottom or on either side of the bottom, screwed into the pressure valve position - It might be elsewhere, but there will be a sensor with a wire on it if it's there and it should be somewhere in the sump vicinity. If you remove that wire, the temp gauge (engine running) should go to zero.  If you don't find another sensor, then I suspect that the temp gauge wire might be unconnected and/or grounded somewhere in the back, causing a high reading on the gauge all the time.

Once you have found the wire/sensor that affects your temp gauge, you'll need one like it.  Show us with a photo and maybe we can help with a source.  My guess (and that's all it is at this point) would be a sensor that is compatible with a VDO gauge, since even the Asian knock-offs seem to work with VDO sensors, but where it is located may mean different threads than the one near the distributor.  We won't know until you find it.

Good luck!