T-Bear Posted March 11, 2015 Posted March 11, 2015 Hi all, I have a 350GT... (350z 4 seat version) which has a weird overheating problem. Start up - Fine Warm up - Fine Idle for 2 hours - Fine Drive off - Overheating within 2 mins Coolant - moving round Heating - blows hot Leaks - None Compression test - fine Exhaust gas in coolant - none (indicating its not head gasket) Local garage has it (manager is an ex 350z owner) and they're a bit miffed Coolant is bled through properly.... and it only overheats when in gear and moving; she'll sit all day on idle. Tomorrow they'll be taking out the temp gauge & coolant pump to test properly. Suggestions welcomed!!! Quote
jimboy2 Posted March 11, 2015 Posted March 11, 2015 Why are you leaving it idling for 2 hours????? Quote
T-Bear Posted March 11, 2015 Author Posted March 11, 2015 Why are you leaving it idling for 2 hours????? Out of curiosity to see if it over heats... (prob was nearer 1 hour though) ... not a glimmer of needle heading north. Quote
GT4 Zed Posted March 11, 2015 Posted March 11, 2015 (edited) Prolonged idle is bad for cams but I guess this was a test not a habitual practice. Sounds strange but some extra info could help. Did this heating issues start de novo or after coolant change? How soon/quickly does it overheat? Is this in every driving condition eg traffic or extra urban? Did you have any coolant in the spill over tank when you first checked this with the heating? Have you tried re bleeding the system anyway from the valve at the back? I presume the above tests in your first post have been carried out by the garage? Yes checking the pump and thermostat is imperative. But it should be worth noting that the coolant can be notoriously difficult to bleed air from and should not be overlooked. Edited March 11, 2015 by GT4 Zed 1 Quote
T-Bear Posted March 11, 2015 Author Posted March 11, 2015 Prolonged idle is bad for cams but I guess this was a test not a habitual practice. - Just a test to see what happens Sounds strange but some extra info could help. Did this heating issues start de novo or after coolant change?- Out of the blue - nothing done to it for 1mth prior How soon/quickly does it overheat? - within 2-3 mins Is this in every driving condition eg traffic or extra urban? - 1st & 2nd, low revs around the industrial estate next to garage. daren't take it on road to test Did you have any coolant in the spill over tank when you first checked this with the heating? - tanks filled to correct levels. Have you tried re bleeding the system anyway from the valve at the back? - coolant correctly put in, valves undone, aircon on full etc... I presume the above tests in your first post have been carried out by the garage? - still at garage & yes. Yes checking the pump and thermostat is imperative. But it should be worth noting that the coolant can be notoriously difficult to bleed air from and should not be overlooked. - the garage owner is an ex 350z owner & is adamant it's been done with no air in system. If air is in system, would it not would boil over at idle? Quote
Zod Posted March 11, 2015 Posted March 11, 2015 (edited) Had similar symptoms in the missus' car, no overheating on idle but after a half hour drive the needle started creeping up. The thermostat was jammed closed, replaced and all was fine. Edited March 11, 2015 by Zod 1 Quote
ZMANALEX Posted March 11, 2015 Posted March 11, 2015 What he has said ^^^ Check the stat. Alex. 1 Quote
Tricky-Ricky Posted March 11, 2015 Posted March 11, 2015 You mean you have a Skyline 350GT! although it could be an air lock or thermostat problems, by what you describe its starting to sound like a head gasket to me, the fact that it can sit and idle for and hour and then only overheat when the engine is put under load. I would run a sniffer test on the coolant, Has the engine recently badly overheated ? Quote
T-Bear Posted March 13, 2015 Author Posted March 13, 2015 Hi all, Another day and another chat with the garage...... Sniffer test yielded no gasses in the coolant. They've changed the thermostat which was partially siezed. Overheating problem is still there.... Odd thing is that the pipes in and out of the rad are hot but the rad fins are cold!! Either their battling an air lock in the rad or the rad has a blockage of somesort - its being pulled out to be pressure tested. Also, their main mechanic is still pretty certain its a head gasket but is eliminating all the smaller issues first. I've known no overheating issue since ownership and the previous owner drove like an undertaker and racked up hardly any miles. Problems... just like busses . Quote
Tricky-Ricky Posted March 13, 2015 Posted March 13, 2015 Have they tested the rad to see if it flows OK? a partial blockage would give those symptoms, it could also be an air lock, however a mechanic should have no problems bleeding the system. Quote
T-Bear Posted March 16, 2015 Author Posted March 16, 2015 Now driving my car again..... New thermostat and it's not overheated.... yet. Bit of steam coming out on it's first drive but not loosing coolant. Hopefully just residue - fingers crossed! Quote
gsexr Posted March 16, 2015 Posted March 16, 2015 (edited) Could be a partial blockage in the rad, hence it overheats when you drive it because there is not enough water being cooled down by the air flow due to the reduced water flow. Whats the age/mileage of the rad. Could be a worthwhile thing to change to eliminate it before you do need a head gasket from overheating. Edited March 16, 2015 by gsexr Quote
T-Bear Posted March 20, 2015 Author Posted March 20, 2015 Righty..... Car is back with me and behaving I can hear water trickling from behind the dash after 2mins of driving. Guessing that means an airlock in the heating system? Rad is now heating up properly & gauges are behaving. She'll be on the ramps on Monday to see if we can find the tiny hole in the cooling system somewhere in the front of the engine bay -still steaming a teeny bit but no real drop in pressure. Mileage on the car is about 45k (mixed km&m) so heads really shouldn't need doing. Is there a best thread for getting coolant in without airlocks? Quote
ZMANALEX Posted March 20, 2015 Posted March 20, 2015 Do you mean coolant as in water or coolant premix as in anti freeze? If steaming is due to loss of coolant then simply pressure test the system to induce the leak. Quote
T-Bear Posted March 22, 2015 Author Posted March 22, 2015 Hi, Coolant = Premix (50%distilled) Monday should be the pressure test... Quote
ZMANALEX Posted March 22, 2015 Posted March 22, 2015 If you drain the block and the rad to get the pre mix in, then you will have to carry out a full bleed of the system. If you only drop the coolant from the rad, then bleeding will be easier. Quote
T-Bear Posted March 22, 2015 Author Posted March 22, 2015 Just looking to try to top up the coolant mix and get rid of the air in the system Will be just topping up the rad Quote
T-Bear Posted March 25, 2015 Author Posted March 25, 2015 She's behaving..... What a bloody airlocks in these are. Quote
GT4 Zed Posted March 25, 2015 Posted March 25, 2015 I'll keep topping up coolant and bleeding air from the valve at the back. A couple of times after a hard drive so do it. Squeezing the hoses vigourously before and bleeding with the rear of the vehicle raised or at an incline helps get the air bubble to the valve which is the highest poit in the system. If there was space in the engine bay I would certainly put a breather system in my car to absolutely banish any air lock in the system. 1 Quote
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