ClubRoadster.net banner

1 - 5 of 5 Posts

·
Registered
Joined
·
390 Posts
Discussion Starter #1
Okay, so I am having difficulties with my water temperature gauge (I think). I have a VDO mechanical gauge, which has it's bulb in the top radiator hose. Several weeks back on my way to a trackday on the M2 my car did not get past about 60*C (on the gauge) until after about 30 minutes or more of driving. Initially I thought it was because of the cold weather (not rugging up cold, but was jumper cold), and/or dead thermostat. I didn't have time to change it, but a week later doing the same trip I found that the temperature went to about 110*C while stuck in a 40kmh zone. I was in third gear, always am, and was not stuck behind anyone. The temp gauge on the dash did not move.

After these events I thought I would pull the thermostat and check its functioning. I put it in a saucepan and boiled the water. It started opening at low 80*C, and was fully open by about 84*C, which is well within specification I believe (correct me if I am wrong). So I put it back in and went for a drive. This drive happened to be a couple of trips to Nemo's house in the hills (30mins from my house). On the way back I went through a twisty road (by no means pushing the car hard, as I did not exceed the speed limit at all), with the last stretch being a long stint on Mona Vale Road (a long, straight road near home). When I parked the car in the driveway I noticed that the temperature gauge was reading beyond 120*C. Upon seeing this I was like FECK!!! I turned the ignition back on, but the fan didn't cut on, neither did the motor/radiator feel hotter than normal, and the dash temperature gauge was reading just cooler than middle as well. I watched the gauge and over the space of about 5 minutes it went from 120*C to 80*C to 100*C.

Today I took the gauge out and went back to Rare Spares at Prospect, where I purchased it. They had the smart idea of boiling it in a kettle, and it worked fine (read 100*C and did not go beyond), so it would appear that it is fine. This is really frustrating, because the main reason I got a mechanical gauge is because there is so little to go wrong on it!!

So I have some questions now:
-what could cause these unrealistic temperature readouts
-rare spares guy mentioned that it could be airlock in the pipes, but then the system hasn't been drained for a year now, and nothing has been changed until last week when I drained the top tank to remove the thermostat. Would an airlock create those readings?
-also, ever since I got the gauge it reads about 60*C when it first gives a reading (being in the top hose, no hot water would reach the bulb until the thermostat opens, which suggests that the thermostat is opening at 60*C, but I know that this is not the case). I would expect the mixing of the hot water from thermostat and cold water in top hose to create some difference in temperature, but 20*C, is that reasonable?

Thanks for any of your help
 

·
Supporting Member
Joined
·
1,376 Posts
Funny I had the exact same thing happen to me yesterday. Did you change your thermostat yet?? Cause I took mine out and did the same test but I also checked the thermostat for binding. For example the thermostat DID open but it would be real sticky at one point and then just push open real quick after it was stuck. So in other words my thermostat was binding which was causing my temp guage to fluctuate. Also your water pump might be on its way out. When you start your car cold w/ the radiator cap off let it get up to operating temp and wait for the thermostat to open. W/ a flash light look into the top of the radiator and when there thermostat opens up you should see your coolant flow through the top of the radiator. If you don't see this you could have a faulty water pump... Hopes this helps. GL.
 

·
Registered
Joined
·
390 Posts
Discussion Starter #5
I have not changed the thermostat, because I didn't think it necessary after checking it. It didn't appear to be sticky at any point? In terms of my water pump, it was brand new less than 5,000kms ago
 
1 - 5 of 5 Posts
Top