Coolant temp goes down after high rpm

[woz_106]

Hi guys,

I was on my way home from work in the week which is a little motorway involved. The car was getting close to operating temperature as I got on the slip road. As I had to accelerate to join the motorway I looked down and my temp gauge looked lower than I had recently seen it. I put this down to maybe it was me after a long day and thought nothing of it.

However last night on the way home the car was upto operation temperature as I had been on the motorway for approx ten mins. When I accelerated and I was in 4th at this point so the revs were at approx 5.5k - 6k when I noticed my temp gauge had gone down to a 1/4 rather than at half.

I think it's also been taking a little longer to get warm initially over the past week.

I have a blueprint thermostat in the car at present as I had a overheating issue about 3 years ago which was the head gasket in the end but I changed cheaper components first hence the none oem thermostat.

Do we think I have a stuck open thermostat?

Cheers guys!

[Peter Gidden]

Does it stay at 1/4 or quickly return to normal?

[woz_106]

Sorry peter, it quickly returns to normal...perhaps 5-10 seconds if that.

[Adam86]

Engine rebuild

At least it's doing the opposite to mine lol.

[Peter Gidden]

Sorry peter, it quickly returns to normal...perhaps 5-10 seconds if that.

OK. One other question - does it do once per journey?

[woz_106]

So far yes, but the journey is half hour if that and only 10-15 on the motorway some in traffic. I'm getting no signs of coolant loss and the car will happily sit there idling to itself without any change but I think this week my temp gauge has been sitting one notch lower (I know the standard gauge is useless but it's my only indicator)

[Peter Gidden]

OK, i've seen this before. In two different circumstances. Always perfectly healthry.

Either when joining motorway, or in depth of ice cold winter.

First time thermostat opens, rush of cold water enters engine. Temp goes down for 10 or 15 seconds. Then all water is same temp and gauge returns to normal.

[woz_106]

It's more I've never seen it do it before that's caused concern and I do slot of miles. Owned the car for 4 years and been working in the same place for 2 of those.

Thanks for the reply though peter, I'll try it over the week and see if I can notice it happening more than once in a journey.

If it does happen more than once what would be the likely culprit in your opinion?

Cheers for you help so far!

[jimGTS]

Sounds like faulty thermostat to me.

I've had the same symtoms before.

Slower to get up to temp
Drops when load/boost is applied, especially on a motorway

[kirk]

I have the same problem with my non turbo. It scared the crap out at me the first time as I've never seen that before. Ended up buying a new rad, anti sneeze, stat and temp sensor. Probably a bit over kill but that's me

Turns out it may of been a good call as I've found evidence of rad weld in the coolant. Here's to hoping it wasn't for the pump which I doubt tbh.

[ashley]

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