possible thermostat issues?

hey everyone,

Looking for some help, on a recent road trip my car would not warm up to the normal 90C on the temp guage. I blocked off the rad better, top and bottom with some pipe insulation, and on a shorter drive (60 miles) the temp went up to normal. on the return trip though, as soon as i would turn our interior heat on, the temp would drop just off the hash mark at 90 degrees. After reading through some of threads on here im thinking its our thermostat. maybe its stuck open, so when i turn the interior heat on its draws the heat from the rad system, causing the temp to drop slightly?

any thoughts?

Definitely the thermostat. Mine did the same thing, only in much warmer weather. The old one was opening at 60 C, the new one started opening at 83 C. This was done with a hot plate, pot of water and a verified old school mercury thermometer.

Yes, new thermostat cured the slow-low heating issue.

Yup. T- stat. Interior heat is stolen from engine, normally not an issue, but when it's cold.....brrrr

If that don't fix the problm , look at 3 coolant heating glow plugs located in coolant goose neck near vacuum pump.

The coolant glow plugs are for loading the engine because increased load on the alternator means more fuel must be injected to maintain idle speed. This smooths out the idle (ECU can load the engine as well as increase the speed, a push-pull control) and also heats the coolant (minor load, about 30 amperes at 12 volts is 360 Watts or less than 1/2 Hp).

Keith, is there a way to test the t-stat in the car to see if it is opening too soon? I too have my radiator blocked off and it seems to take close to 15 minutes for the temperature reading on my scan gauge to reach 180, and this is with the heate blower OFF. The lower radiator hose is always cold to the touch, but the upper hose does get hot. Once I do turn on the heater blower the temperature drop ~ 5 degrees, but I thought this was normal.

Thor said:

If that don't fix the problm , look at 3 coolant heating glow plugs located in coolant goose neck near vacuum pump.

Click to expand...

Shouldn't coolant glow plugs throw a MIL? That being said it only takes a couple minutes to pull out your multimeter and test resistance on the coolant glow plugs.

I don't think the coolant GP's are monitored by the ECU.

Nope those are not monitored glow plugs.....a given the cost of replacing them, theymaremfrequently ignored.

Testing a tstat....good thermometer, boil some water and observe....trouble is, for the cost, once removed, just replace and go...

Thanks for info Keith, was not sure of total function of them.
gallaj01 only engine glow plug turn on light.

I just changed the t-stat on my Golf a couple of days ago. The engine is running hotter than before, average 195 compared to 185F. I do have the radiator blocked off. On a BEW the bottom flange bolt is very difficult to get to with the alternator in the way. I suggest using a long, ball end 5mm allen socket.

For reference, an actual coolant temperature of 165 - 215 is indicated as 190 on the gauge. So if your gauge isn't straight up, your coolant temp is under 165°F.

If the temp remains below 165 will that have an effect on mileage?

Yup, increased engine wear also.

Yes. I would consider 165° to be the minimum of the acceptable operating range, although extended idling in traffic in very cold weather with the heat on will drop it below that -- not much you can do about it.

I just changed the thermostat on my car (and installed a Frostheater while the system was open) on December 26. Previously, my coolant temperature never got above 163 Fahrenheit according to my Scangauge. After replacing the thermostat, it's now getting up to about 190-193 degrees on long distance trips.

I actually get usable heat and I'm getting better fuel economy now as well. The thermostat, O-ring and a new housing cost something like $40 from 1stvwparts. It was a wise investment for sure and the thermostat replacement wasn't difficult or time consuming to do.

My new t-stat, from idparts, is now showing temperatures of 195-197. I changed it last Friday, so I would think that any air would be purged by now. Today the ambient was in the teens and my SG still went as high as 197.

Last Friday I changed my t-stat that I bought from WorldImpex, and the scan gauge is now reading as high as 195-197. Today with the ambient temps in the teens the SG went as high as 197 while on the highway. I would think that any air in the lines would be purged out by now.