GU thermostat

Submitted: Monday, Apr 11, 2005 at 18:02
ThreadID: 21969 Views:2314 Replies:14 FollowUps:16
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Just after opinions...........what would be the result if I decided to totally remove the thermostat from my 4.2GU?
I thought I may just try that before even fitting a NEW unit. If it just means it'll take longer for the temp gauge to reach normal operating temperature, is this such a bad thing?
I just wanna try and streamline the whole coolant circulation process and stop my temp gauge from going up.
The other thing I still wanna do relates to the lower radiator hose. I either wnat to insert a stainless steel coil spring or cut out the middle bit of the (longish) hose and replace with a length of copper pipe. Either of these methods might stop the bottom hose from sucking in on itself (if indeed that is one of the things that is happening).
Anybody have any thoughts?
Thanks in advance,
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Reply By: Member - Banjo (SA) - Monday, Apr 11, 2005 at 18:13

Monday, Apr 11, 2005 at 18:13
Roachie .... take it right out ? Have none ? Stand well clear.... the thermocrats will be online soon. ... you're in for a pasting with that question I reckon. ! Far as I know, it will warm up really slowly (and engines run best hot someone said). Also in very cold weather, might it not get to proper running temperature at all ?
AnswerID: 106199

Follow Up By: Member - Roachie (SA) - Monday, Apr 11, 2005 at 18:29

Monday, Apr 11, 2005 at 18:29
Thanks mate,
I know it'll take longer to heat up, but looking at Andrew's response, he probably has a point as well....

FollowupID: 363229

Reply By: Andrew (Whyalla) - Monday, Apr 11, 2005 at 18:14

Monday, Apr 11, 2005 at 18:14

The thermostat has 2 functions. As you said, it shuts to enable the engine to warm up faster. It also serves as a restrictor to regulate the flow rate of coolant through the block. If it travels through too quickly it cant "absorb" enough heat and cant dissipate enough through the radiator.

For both reasons, total removal is not a good idea.
AnswerID: 106200

Follow Up By: Member - Roachie (SA) - Monday, Apr 11, 2005 at 18:31

Monday, Apr 11, 2005 at 18:31
Thanks Andrew, I never thought of the second issue you mention, however having fitted an expensive radiator with double the capacity of the original unit, I'd like to think it could cope with the coolant travelling though at an increased speed. Would probably only remove the thermostat during the summer months.
Cheers mate
FollowupID: 363230

Follow Up By: Toy_Hilux - Monday, Apr 11, 2005 at 18:59

Monday, Apr 11, 2005 at 18:59
Not a good idea for total removal. What a radiator specialist recommended for me to try was to pull the middle of the thermostat out, that way it restricts the water flow to a degree. It worked a treat on the old hilux.
FollowupID: 363238

Reply By: Member - Bradley- Monday, Apr 11, 2005 at 19:23

Monday, Apr 11, 2005 at 19:23
the only mod i have ever seen sucessfull to a thermostat, is to drill a 1/8 inch hole in the flange so that any trapped air will bleed out when filling the system, as said, do not remove it all together, it will not get to temp properly, and will even overheat when worked hard.

AnswerID: 106209

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:45

Tuesday, Apr 12, 2005 at 22:45
Thanks Bradley, I've decided not to remove the thermo, but have ordered a new one which should be here by friday, so I can fit it on the weekend.
I've just found out from another question I asked today about thread sizes, that there is a convenient way for me to bleed air from the system in future.
FollowupID: 363471

Reply By: hanson - Monday, Apr 11, 2005 at 19:25

Monday, Apr 11, 2005 at 19:25
Roachie.... digressing a little, wot sort of radiator u put in and pricing??? interested to know
AnswerID: 106210

Follow Up By: Member - Roachie (SA) - Monday, Apr 11, 2005 at 20:47

Monday, Apr 11, 2005 at 20:47
G'day Hanson,

I got a big shiny aluminium jobbie from PWR in Qld...cost...$1,100-.

It's a well engineered unit. Has the threaded holes in the bottom for the 2 switches that control the air con shut-off and the turn-on of the air-con fan only. I have disconnected the 1st mentioned item (there's an electrical plug you can just unplug) on the passenger's side which means that I can now decide if/when the air con gets switched off.

The only 3 problems I had with it have been:
1) When I installed it I couldn't re-install the plastic shroud. That is because the radiator sits back about another inch or so closer to the motor and the shroud is difficult/impossible to get back in. However, without it you run the risk of losing a few fingers, cos the fan is fully I cut the shroud off about 4" from the top and just installed the top bit. I know that this probably means the original fan isn't working as efficiently as it should, but don't forget there are 2 electric fans (the air cond one and another one I put in myself) that blow air through from the front as well).

2) On a trip to Cape York last September/October I was losing coolant. I tracked down that the small pipe which exits the radiator at the top (below the cap) was narrower than the original. This meant the coolant was travelling to the expansion tank when the radiator got hot, but as it cooled down the coolant was not being sucked back into the radiator because there was not a proper seal at the junction below the radiator just sucked air in.

3) also on the Cape York trip, the bottom tank suffered 2 fractures where the 2 reatining lugs went through their respective body mounts. I think this was a product of the severe corrogations. I managed to get that re-welded at Seisa.

I thought the bigger radiator would have cured my over-warming problems; but no it hasn't.


FollowupID: 363257

Follow Up By: warthog - Monday, Apr 11, 2005 at 22:52

Monday, Apr 11, 2005 at 22:52
Hi Roachie,
I just spent $800 getting the standard alloy core replaced with a copper one that has more cores spaced closer together. I reckon it might be a bit more efficient than the std one but the pwr would have to be better again. I also had the injector pump timing done and the fuel cut back a bit with the aid of a pyro and I think this had more effect on over warming issue than radiator. If its not the bottom hose it must be a tuning issue? Have you got the 3" exhaust and dump pipe? Don't know if that helps engine temps but it sure helps them go better.
FollowupID: 363279

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 14:29

Tuesday, Apr 12, 2005 at 14:29
Yep Warthog,
Have got the 3" exhaust and special (bigger) dump pipe goes better than when it had the standard exhaust.


FollowupID: 363363

Reply By: Boo - Monday, Apr 11, 2005 at 19:46

Monday, Apr 11, 2005 at 19:46
Evening Roachie...
I have had quiet a lot of experiance and knowledge in this exact topic. (my old man was a radiator and coolant specialist in Cooma for over 50 years after which my brother then took over the buisness). The complete removal of the thermo will have very little detramental effect on the system apart from taking a little longer to heat up. It will mean your choke is operating a little longer which also uses slightly more fuel while its still open, the motor itself is designrd to operate at a given temperature and untill its reached it wont give 100% economy or power but once the motor warms slightly if you can pick the difference your better than me. Since I started driving my own car many, many years ago I have regularly taken the thermo out each spring and replaced it each autumn. Even if you do like to run one in the system all year you still should replace it annually. 3 out of 4 ( a very large portion anyway) overheating problems and blown seals are caused by the little buggers not operating properly. I do agree with the suggestion from Toy_Hilux as to ripping the centre out of them and slowing the water slightly but thats only so it will warm up a little quicker. (have done it many times especialy in my Falcons). I also recomend ripping the little toggle out of the breath hole in the face of them to prevent air locks especially when you first fill the radiator back up. As for the bottom hose sucking in... throw it away and put a good quality new one on, once they get soft there not worth the worry.
Should stire a hornets nest with that one...
AnswerID: 106214

Follow Up By: Member - Roachie (SA) - Monday, Apr 11, 2005 at 20:50

Monday, Apr 11, 2005 at 20:50
G'day Boo,
I spent 3 years in Cooma from 1998 to 2001...interested to know who your family are there....if they were still there during those years I might know them?

I've been thinking that the full removal of the thermostat shouldn't cause any problems, but your comment about "choke" doesn't apply as mine is a diesel.

Thanks for your response.


FollowupID: 363259

Follow Up By: Boo - Tuesday, Apr 12, 2005 at 00:09

Tuesday, Apr 12, 2005 at 00:09
Good to hear from a semi-local....
Send us a mail and I'll get back to you.

FollowupID: 363293

Reply By: Member - Robert (WA) - Monday, Apr 11, 2005 at 21:50

Monday, Apr 11, 2005 at 21:50
Hi Roachie
Its not a good idea to run a diesel too cold as there is a temp switch for the glow plugs and the glow plug will stay on longer if it is to cold
the cooler you run the engine the higher the wear rate on the piston bores

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AnswerID: 106240

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:48

Tuesday, Apr 12, 2005 at 22:48
Thanks for your input mate....I'm gunna go with the concensus and keep a thermo in there....I've ordered a new one as the one there now is the original.
FollowupID: 363472

Reply By: Stew53 - Monday, Apr 11, 2005 at 23:00

Monday, Apr 11, 2005 at 23:00
As a Diesel fitter I would not recommend the removal of a thermostat, when the vehicle was new it had a thermostat and would not have overheated, so if it overheating now there must be a logical reason why, I am not sure of the amount a Nissan thermostat opens somebody may have a manual and can tell you, what you can do is remove the thermostat place it in a saucepan and cover with water and heat until a rolling boil, at this stage the opening could be about 10-12mm at a guess , you may even be able to see old wear marks on the stem where the thermostat used to work and now is not opening as far, as cheap insurance you could buy a new thermostat and boil it up and compare opening dimensions this would confirm the reason for overheating if the old thermostat does not open as far that is.
You need to get to the bottom of the overheating, as you may feel good about the temp gauge hardly moving around town but one day on a trip somewhere loaded up with all your gear the conditions will be right i.e. hot day, steep climb, etc. and it will happen again.
AnswerID: 106262

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:50

Tuesday, Apr 12, 2005 at 22:50
Thanks for your words of wisdom Stew...believe me mate, I am trying to get to bloody bottom of this matter.
FollowupID: 363473

Reply By: muzzgit (WA) - Monday, Apr 11, 2005 at 23:42

Monday, Apr 11, 2005 at 23:42
I'm not a diesel mechanic nor a radiator repairer, but I have seen an article in 4WD Monthly about overheating 4.2 Patrols. Better results were gained from making sure the fuel delivery system is properly tuned (less fuel), increasing the size of the turbo blades (more air), and fitting a less restrictive exhaust (less hot gasses).
AnswerID: 106271

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:53

Tuesday, Apr 12, 2005 at 22:53
I know you're right mate, about the timing and fuel delivery needing to be spot on. I was concerned about that, so I fitted the EGT gauge to measure exhaust gas temps.....normal. I am told that if it was over-fueling, the EGT's would be up pretty high. So I'm back to the cooling system itself.
I'll get it worked out if it's the last thing I ever do!!!
Cheers mate
FollowupID: 363474

Reply By: Member - Hugh (WA) - Tuesday, Apr 12, 2005 at 00:26

Tuesday, Apr 12, 2005 at 00:26
Hi Roachie,

Personally I wouldn't remove the thermostat permanently, as the EMS will rely on temp sensor input for calibration. There is certainly going to be warm-up functions that alter injection timing, fueling, etc. If the engine doesn't get warm then the engine won't be operating efficiently.

I can understand the urge to do so, particularly if the engine is running warmer than it should. Unlike gasoline engine, over fuelling will result in higher EGT and increase coolant loading, so the comments about having the injection pump, boost, etc correctly setup certainly apply.

However I was interested in your comments regarding the lower hose. Was the hosing raplaced with the PWR radiator or is this carry over from std? I have tested a lot of engines on dyno's at work and if there isn't a spring in the suction hose (from radiator to water pump) there are invariby problems. Hose collapse will reduce the hose x-section considerably (I've seen them close right up) with resultant impact on coolant temp. The problem becomes more prevalent on longer sections. Our dyno installs always end up being customised hosing, though we opt for solid tubing for large runs or spring within hose for shorter runs (we use hose that has this built in). I think your idea for bottom hosing has merit. My 2.8 GU has solid tubing in lower pipe work, with two short sections of hose. A pain for spares but obviously done for a reason.

The other factor than can cause problems is air locks due inadequate bleeding of the coolant system. Some engines can be a real pain to bleed, so you need to be careful to get rid of excess air.

I hope this helps in some way. Good luck with your trials.

AnswerID: 106281

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:56

Tuesday, Apr 12, 2005 at 22:56
Thanks Hugh, but with mine being a 4.2 (old banger technology, so no EMS computers etc), I'm not sure the fuel delivery would be affected by the coolant temp etc....but as somebody else said, if it's running too cold it could have an effect on the glow plugs.
I'm gunna leave the thermostat (a new one will be bought) in and persevere some more.
FollowupID: 363476

Reply By: Member - Pesty (SA) - Tuesday, Apr 12, 2005 at 00:48

Tuesday, Apr 12, 2005 at 00:48
Some great advice there Roachie, you know what my answer will be, as i have told you many times, one day you will come outa the closet !!!
AnswerID: 106282

Reply By: Member - Camper (SA) - Tuesday, Apr 12, 2005 at 12:49

Tuesday, Apr 12, 2005 at 12:49
I thinl you are getting the message, Roachie: test the thermo if it is malfunctioning fit a new one. If you run without one your motor will not run hot enough which will mean the efficiency of the deisel combustion will bo to pot seriously any your motor will not be able to evaporate the water which is a product of combustion of fuel so that you will get water in your oil evidenced by cream coloured gunk in the oil filler cap.
Some diesels are even tuned by measuring exhaust temp as temp is important to the function of what happens in the combustion chamber at ignition time.
Always happy to share my badly informed thoughts.
AnswerID: 106341

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:58

Tuesday, Apr 12, 2005 at 22:58
Thanks Camper.....your advice will be heeded.....
Hope to cya up this way some time (Yorke Peninsula; Kadina).
Cheers mate
FollowupID: 363477

Reply By: G.T. - Tuesday, Apr 12, 2005 at 14:58

Tuesday, Apr 12, 2005 at 14:58
Another issue not covered by the past replies is that many (not all ) thermostats have a foot valve which blocks off the by pass system when open. If the by pass is not blocked off it will allow hot water to be pumped back into the engine block without going through the radiator and getting cooled with predicitable results. I don`t know if your vehicle has this feature or not, check with Nissan to see.

Also if your fan shroud had to be modified to fit with the new radiator, ie parts missing , my guess is that you are not getting the air flow through the radiator that is required despite it`s better cooling capacity. I would be talking to the manufacturer of your radiator to see if they can help you.

What ever you do , don`t take the thermostat out. You will not solve your problem by doing this. Good luck , regards G.T.
AnswerID: 106363

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 23:00

Tuesday, Apr 12, 2005 at 23:00
Thanks GT.....thermostat will be renewed and kept on board; but I haven't previously heard of this by-pass and foot-valve etc. Strewth, something else to worry about......lolol
FollowupID: 363478

Reply By: Michael ( Moss Vale NSW) - Tuesday, Apr 12, 2005 at 21:43

Tuesday, Apr 12, 2005 at 21:43
Roachie, one thing it will do is cost you horsepower and higher fuel consumption, if you run it cold. also your heat exchange will be less efficient.
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AnswerID: 106440

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 23:04

Tuesday, Apr 12, 2005 at 23:04
Okay Michael; that does it!!!!! I can handle anything else......but not a cold shower. If the heat exchanger doesn't function properly SWMBO won't want to go camping anymore and I may as well sell the whole damn lot.....guess what?? the thermostat is gunna be renewed and I'm gunna see if I can get a new bottom hose fabricated using some of the original bends and whack in a piece of stainless pipe in between.
FollowupID: 363479

Reply By: Stew53 - Wednesday, Apr 13, 2005 at 21:56

Wednesday, Apr 13, 2005 at 21:56
Roachie another thing to look at, I'm not sure how the heat exchanger works but I presume its plumbed into the heater hoses, the circulation for the heater comes about by one hose coming from the top of the engine before the Thermostat , then to a valve on the firewall to regulate the flow/heat then drawn through the heater core by suction from the water pump, the hose for the return is before the water pump, Circulation through this system is about 30-40 PSI, not to be confused with the 10-15 PSI system pressure in the cooling system pressure. What I'm getting at is if the heat exchanger does not have any taps on it to stop the flow whilst you are driving Coolant will take that route back to the water pump and not go through the radiator and be cooled, a similar thing happens when people loop heater hoses to bypass heater cores . I've found this on a number of old cars and trucks.
AnswerID: 106603

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