Coolant temp never reaches 90oc

[Jonnyboy]

Having read through Most of the threads I can find I'm still unsure as to wether my main stat, temp sensor or smaller bypass stats need changing.

The polar FIS reads about 65-70oc for water temp and the analogue gauge on the dash sits half between 0 and 90 let's say. To be honest I'm just going off the digital reading as it should be most accurate. It gets up to 70oc degrees pretty quickly 3-4 miles but then never gets any higher even on a long drive never seen it get to 90oc!!

What could be causing this issue the main stat? or could the coolant be at 90oc and the sender not be relaying the correct temp measurement?

Any help appreciated.

[SiofChester]

Going through exactly the same right now with mine. If I go in traffic, it'll hit 90 but no more. Going to replace the sender unit as the gauge moves very quick, almost too quick for the actual temperature to move that much. But from all the reading, it's the stats, just trying to put off the job of the main stat....

[Danbear79]

I had the same problem but when I had the cambelt and pump done, I had the thermostat changed and it's been sitting at 90° bang on once warmed up

[GrayMK5GTI]

http://www.mk5golfgti.co.uk/forum/index.php/topic,90088.0.html

Try the stat first 

[SiofChester]

Ive got one of the inline stats on its way, going to fit it at the weekend so will report back if it fixes my problem or not

[lukemk5gti]

Have the same problem. Started doing weekly 400 mile round trips where it sits around 75deg thus being less efficient so it's actually costing me money.

Booked in to have main thermo replaced on Monday at a very fair rate of 225euro vs 400euro from VW direct.

[Jonnyboy]

So does the main stat control the coolant temp and maintain it at 90oc and the inline small stats make it get up to full temp quickly.

So if the main stat is shot then it will never get up to full temp, but it will get upto 70oc fairly quickly.

If the inline stats have had it then the car will take ages to get to 90oc but once there it will maintain that temp because that's the main stats job?

Just trying to clarify what the roles of the stats are before I order the parts.

[skard]

I believe on a GTI the stat opens at 80c, on an ED30 at 87c

[lukemk5gti]

So does the main stat control the coolant temp and maintain it at 90oc and the inline small stats make it get up to full temp quickly.

So if the main stat is shot then it will never get up to full temp, but it will get upto 70oc fairly quickly.

If the inline stats have had it then the car will take ages to get to 90oc but once there it will maintain that temp because that's the main stats job?

Just trying to clarify what the roles of the stats are before I order the parts.

I don't think that's right. From what other members have shown. They only reach 90 when stuck in traffic and sit around 75 on motorway.
After replacing the main thermostat it solved the problem.

[Jonnyboy]

Went out in the car today on a run through town with traffic etc about 7 miles each way. The temp on digital meter never went above 67oc, it didn't really drop when I was coasting and it didn't go up in traffic. It didn't take long to reach its max temp of 67 probably 2-3 miles.

So is this the main stat stuck open and stopping the temp increasing? By replacing the main stat will that fix the problem of not reaching 90oc as its bugging me now, I am sure it's affecting the mpg.

[Jonnyboy]

Just noticed this plug/sensor that looks like it's been glued together at some point. What is it would it be affecting the temp gauge on the dash?

[mac456]

Mine does this, well similar. Mine actually gets to 90 it just takes a very long along time and sometimes drops back down.  Now its colder its alot worse.

Do you guys fully rev your cars when this happens? will the oil temp be effected by this?

[Jonnyboy]

My oil temp is around the same as the coolant so about 67oc

[SiofChester]

Well I monitored the coolant temp on the climate control and it never got to 70, traced every coolant hose and could find no sign of a secondary thermostat so went ahead and replaced the main stat. Instantly warmer, proper coolant temperature stable at 92c , hoping for some better MPG on the daily commute tomorrow. The heaters work much better too

[edd30]

Very interesting Si - Did you replace it yourself ?
How difficult was it ?
How many stats are there on our cars ? (mine is a ed30 if it makes any difference)
Any one got any photos of where these things are located ?