evo828 Posted October 27, 2009 Share Posted October 27, 2009 I've read all posts regarding V8 overheating - but still have some questions: my specs: 3.9 V8 auto (1998 with serpentine); megasquirted + EDIS; cca 3000km ago - done amongst others also thermostat and composite headgaskets - also bearings; valves, cams, lifters etc when warmed up - car runned very well within 80-85 degC range all the time (even when ambient temps were 30degC and slow offroading - it never went over 90 degC. Sunday: Took the kids for a smal track we have close by - somu up/down/shaking cca 10minutes and then on the way back saw the temp gauge climbing up. Connected laptop to see the coolant temp - it was 100degC and climbing (slooowly) up. Stooped the car - the electric fans kept running (as they should). checked: - thermostat 88degC spec (was fitted new some 3000km ago) - radiator upper hose hot; lower hose less hot - heating works fine - helps to decrease the temp to approx 95degC - but not lower - coolant level on the spot as it was for months (the green anti-freeze stuff is there) - after it cooled to cca 80degC - started the car with open expansion tank to see if something is going on there while reving the engine etc. - no bubbles - no significant action happening inside there - just a very slow motion of the water is visible when giving it revs - surprised as I would expect more action/water moving inside there when reving the engine (?) - took the spark plugs out - look as they should - no "steam wash" signs at all (but it was only 20km driven in this "overheating" state). - the engine still starts very well (whether cold or hot) - no white smoke or missfire Monday: - the engine still starts very well - no white smoke or missfire - I've let it warm up while idling - warming up at ususal speed - when it went over 93 - I turned the eletric fans on (A/C switch) - this has NOT decreased the coolant temp - went for a short ride (5km) - inreases slowly to 100 level - fans still do not help - heating turned on - temp decrease by cca 5 degc and +/- stays there What could be the reason for this sudden overheating (the ambient temps are low now 10-15degC) - has the offroad shaking moved/blocked with some carp the radiator passages suddenly so the efficiency decreased so drastically? Or Water pump giving up? How to check? Any hints and tips will be appreciated. Flushing the rad is not very efficient (based on some comments here on the forum - new one is over 200pounds). The gaskets are composite and relativelly new. I cross my fingers that this is not the cracked block issue - as this would be the end of my LR experience Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted October 27, 2009 Share Posted October 27, 2009 As you say, water pump or radiator, leaning towards the latter, as I assume you checked the water pump when you had it apart...? Feel the radiator when it is hot(carefully!), if the bottom is still cold then you probably have a sludged-up radiator. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted October 27, 2009 Share Posted October 27, 2009 Have you checked the thermostat is working? Was it genuine parts? Did you fit it the right way up (with the jiggle pin at the top)? I had a spate of about 3 thermostats which either stuck or airlocked (not all have the jiggle pin / hole at the top to allow air past) and led to overheating but only intermittently. One would hit ~100deg then open then sit forever at 88deg until you turned the car off and let it cool down again. A genuine stat cured it. Quote Link to comment Share on other sites More sharing options...
DiscoClax Posted October 27, 2009 Share Posted October 27, 2009 I'd agree with Mr Freezer. Suggest you start by replacing the thermostat with a genuine item (after checking the new one works in a saucepan on the stove, thermostat suspended with wire so it doesn't touch the sides/bottom). Make sure it starts to open at about the specifed temp and is fully open within 10 deg C of cracking open. It's a bugger when you replace the stat for a new unit and then work out later it's not quite right either... Been bitten... Check the "old" one also to confirm it's the culprit. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted October 27, 2009 Share Posted October 27, 2009 The stats that caused my problems would work if submerged in a pan of water, but they airlocked when at the top of an engine cutting the centre out worked (you need a bit of restriction, running with no stat can lead to steam bubbles in the heads) and proved that it was airlocking. Quote Link to comment Share on other sites More sharing options...
evo828 Posted October 27, 2009 Author Share Posted October 27, 2009 thanks for the info - didn't see the water pump and thermostat myself when the "partial" overhaul was done - the car belonged to my friend who was doing it for himself. I bought the car later - when he needed to sell it. I stated that "stat checked" - because I thought when the upper pipe from thermostat to radiator was hot - that the water is flowing. I will empty the radiator today to see if some stuff will come out. Also will remove and test the stat - as I do not have a spare one - should I try to run it without to see if it helps? Or should I make a hole in it? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted October 27, 2009 Share Posted October 27, 2009 As I said, the stat should have a small bypass hole (often with a loose "jiggle" pin in it) which must be at the top when fitted. If it does not have a hole, drill one (min. 5mm) or buy a genuine stat. This picture sort of illustrates the jiggle valve, albeit a Nissan one: http://z.about.com/d/autorepair/1/0/i/4/82097120.gif And the one on the left of this picture is very close to the genuine Rover one: http://www.vtr.org/maintain/stag-topstat.jpg If the stat is not opening properly then the top hose can become warm, but with little or no flow the water in the engine will be boiling behind the stat. Running without a stat is a bad idea for the reason I stated, cutting the centre out is nicer but probably still not the best idea. Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted October 27, 2009 Share Posted October 27, 2009 - after it cooled to cca 80degC - started the car with open expansion tank to see if something is going on there while reving the engine etc. - no bubbles - no significant action happening inside there - just a very slow motion of the water is visible when giving it revs - surprised as I would expect more action/water moving inside there when reving the engine (?) With a cold engine (i.e. the thermostat closed)..... reving to about 2K rpm you should be able to get a mini fountain in the expansion tank and the level will rise quite a lot to the point of overflowing. To see if you have head / block issues, just sniff the coolant tank ............ if either of those problems are present then it will smell strongly of exhaust gaes. At the moment I am leaning towards a faulty thermostat or it maybe that a small piece of debris from your rebuild has jammed it slightly open. Ian Quote Link to comment Share on other sites More sharing options...
evo828 Posted October 27, 2009 Author Share Posted October 27, 2009 update: took the thermostat out - correct type with the hole on the top - however - left it in boiling water for 2 minutes - not opening at all. so need to get a new one with gasket I hope this is the whole story. seems that it let water flow only through the small hole - letting the hose to get hot enough for me to think that stat is opening - weird. Quote Link to comment Share on other sites More sharing options...
evo828 Posted November 15, 2009 Author Share Posted November 15, 2009 now I finally put a new one 88degC spec (with hole up etc). What worries me is now the engine runs at 91-92 degC (based on Megasquirt). Previously it has been cca 83-84 degC (when the old one was still working). What is the correct operating temp for 3.9 V8? Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted November 15, 2009 Share Posted November 15, 2009 The simple answer is whatever it runs at! Car engines never stay at one particular temperture. Even the reading on MS taken from the inlet manifold will be different to the temperature of the liners. As long as it is below 100 and above 80, it will be fine. Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted November 15, 2009 Share Posted November 15, 2009 now I finally put a new one 88degC spec (with hole up etc). What worries me is now the engine runs at 91-92 degC (based on Megasquirt). Previously it has been cca 83-84 degC (when the old one was still working). What is the correct operating temp for 3.9 V8? 88 is correct for the 3.9 .......... only very early 3.5's ran on 74 & 77 ...... the correct running temp will be 88 - 90 ........ your MS sensor cal maybe a couple of degrees off but that is of no importance Quote Link to comment Share on other sites More sharing options...
evo828 Posted November 15, 2009 Author Share Posted November 15, 2009 thank you all for the info. Quote Link to comment Share on other sites More sharing options...
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