Quote:
Originally Posted by SD1too
Hi Bob,
I'm sorry to have to say this but I don't agree with what Michael ( mbonwick) has said here. Your coolant temperature should never drop as low as 79˚. The thermostat is designed to keep it at a minimum of about 92˚. When the car is stationary or slow moving in traffic, this should steadily increase to 104˚ when the slow speed fan should trigger.
Your temperature is varying widely depending upon engine load which is not correct. Your system is not pressurising which means that you won't have the protection of a raised boiling point. When the conditions are right you will continue to lose coolant, but it will be intermittent. Having a 1.8 you're then at risk of the incorrect diagnosis of head gasket failure.  |
The thermostat is not "designed" to keep the coolant at 92˚C at all. It is designed to open at a specified temperature range to assist keeping the coolant temperature at an acceptable level. The overall
system - of which the thermostat is only 1 part - is designed to keep the coolant at a relatively steady low-mid 90s˚C temperature. A good rule of thumb for the 1.8 is coolant temp 5˚C above the rating of the stat (i.e. for the OEM 88C stat, expect temps of 92/93˚C).
The aftermarket stats supplied by DMGRS are rated at 82˚C (so expect temps of 87/88˚C).
The other unfortunate side effect of the DMGRS stat is that it opens/closes over a much larger temperature range than the OEM design, so you get much wider temperature swings when coasting, as coolant (already at a lower temperature as the stat opened earlier) is still circulated round the radiator, removing heat faster than it is generated by the "idling" engine.
As for how I know this? I have both OEM and DMGRS stats and have done a far few comparative trials - both on and off the car. Incidentally, I've always regretted (solely from a research perspective) binning the original PRT from the car which gave a running temp of 96˚C.
Of course, there is a big
IF in my original statement that this is only true if the fitted stat is a DMGRS example - if its not, and is a genuine MGR 88C part, it has obvious started opening early and should be replaced.
Finally, I'm not sure how you can make any conclusion on the correct (or not) pressurising of the system just on the fact that its not spewing steam out everywhere? Bob absolutely should be vigilant in case there is another problem, but at the end of the day it's a 1.8 with a very simple cooling system. Most problems are incredibly simple in nature and don't need a full scientific investigation, and not every K-series cooling issue leads to HGF...
