Sigma Overheating.... Ahhhh!

[H8DAG8]

Hi guys

'84 Mitsi Sigma SE (GV NZ model), 4g63 SOHC 8 valve RWD carby engine.
Recently had a new head put on, new thermostat, new waterpump, new pretty much everything. Radiator is original but got flushed as well as the cooling system.

Has been running fine although I posted on here about the strange rise in temp to (or JUST above) half every now and then.

The other day, looked down at the temp and she was nearly at max H.. shut it off and waited for it to cool right down and limped her home. One overheat shouldn't crack the head right? I let it cool down nice and slowly, didn't put a hose on it or anything. Radiator was still full and nice and green with anti-freeze/boil.

Why in the hell would it be doing this? The bottom radiator hose felt cool at one end when it overheated. The top one was hot.

I'm testing the thermostat today and if it's fine, what could it be? Any idea's? And common issue's like this on these engines?

Any info. much appreciated. Cheers.

[l3004x4drifta]

gday. im sure this is pretty obvious, but is the fan belt at the correct tension? i hope you get it sussed..

[81GL]

Is the cooling system pressurising?

[H8DAG8]

gday. im sure this is pretty obvious, but is the fan belt at the correct tension? i hope you get it sussed..

Hey mate, as far as I know the fan belt is at the correct tension. Any quick "easy" way to double check the tension is correct? The fan definitely spins though, yes.

Is the cooling system pressurising?

Good question, again, as far as I know yes it is. How would I go about checking this?

Thanks guys.

[l3004x4drifta]

there really shouldnt be too much slack in the fan belt at all.. just squeeze the belt hard, and if you have any more than say ten mill of play, that could be a problem.. but as mentioned above, getting the radiator pressure tested(proffesionally, at a radiator specialist) is definitley a good idea (and inexpensive too). to not fully diagnose the problem would be false economy, and could end up in a stuffed motor. give the top radiator hose a hard squeeze, can you tell if there is pressure escaping then? is it possible that the radiator cap is buggered?(buy a new one and make sure its the correct pressure rating, also cheap) the other thing i would check for is an airlock. ie, run the engine with the radiator cap off and let it get to operating temerature. if the level in the radiator drops, top up with coolant (and squeeze the air out of the top hose while doing it). i hope this helps.

[mstrrab1992]

Eh im no expert just gonna throw a few things ur way, blocked radiator - get it flushed, take ur thermostat out and force water through engine, new water pump, not enough air flow through radiator,maybe blocked injectors/carby making it run very lean. Eh idk, no expert but most common i can think of

[mstrrab1992]

Is the cooling system pressurising?

Good question, again, as far as I know yes it is. How would I go about checking this?

Thanks guys.

Take the cap off when its hot.

[mstrrab1992]

Hi guys
Recently had a new head put on, new thermostat, new waterpump, new pretty much everything. Radiator is original but got flushed as well as the cooling system.

faulty water pump.!

[H8DAG8]

Radiator was flushed when the old head was replaced.
Yes when it overheated and the radiator cap was taken off it released pressure.
When it's cold and I squeeze the top radiator hose yes it lets air bubble out.
Have taken the thermostat out now and am just about to test it on the stove in a pot of water.
Will post up if it's sweet or not working soon.

EDIT: Oh and the fan belt has about 2-3mm play and is very firm. So should be sweet.

[Superscan811]

2 things to check.

1. Are you running a fan shroud?
If no, get one and see if that helps. It should only effect the temp when stopped in traffic, not while driving normally.

2. Does your car have an air conditioner?
Occasionally paper and leaves etc can build up in between the aircon and standard radiators. Usually you can't see it unless you remove one of the radiators.
Also check the fins on the Aircon radiator are still OK. Doesn't take much to damage them, even a bit of high pressure cleaning can bend a lot of them over and block airflow for both radiators.

Cheers.

[H8DAG8]

2 things to check.

1. Are you running a fan shroud?
If no, get one and see if that helps. It should only effect the temp when stopped in traffic, not while driving normally.

2. Does your car have an air conditioner?
Occasionally paper and leaves etc can build up in between the aircon and standard radiators. Usually you can't see it unless you remove one of the radiators.
Also check the fins on the Aircon radiator are still OK. Doesn't take much to damage them, even a bit of high pressure cleaning can bend a lot of them over and block airflow for both radiators.

Cheers.

Yep I've got the standard fan shroud.
And no the car has no air-con, factory.

Below is pic of thermostat - just tested, works fine. Errrrrr

[mstrrab1992]

to lean perhaps????idk, maybe not getting enough air flow through the front of it, or ur thermo is to small when at idle it isnt cooling, i know my lancer with the 2.6 astron was overheating (well getting hot) when at idle with a 10" thermo, put a 12" on and its fine now when idling.

[H8DAG8]

to lean perhaps????idk, maybe not getting enough air flow through the front of it, or ur thermo is to small when at idle it isnt cooling, i know my lancer with the 2.6 astron was overheating (well getting hot) when at idle with a 10" thermo, put a 12" on and its fine now when idling.

Had it tuned by a mate of mine who's a mechanic/auto elec. so should be tuned sweet, has 252 grind lumpy cams but it tuned to suit. Air-flow through the front should be fine as it's all factory so nothing blocking the air from getting in and doing its job.

Thermostat too small? Hmm.. I didn't know you could get different sizes! 10"? 12"? Where are these measurements taken from? That sounds huge. When I replaced mine Repco didn't mention any variations in size or options they just gave me the part that was listed for my car.

When the car actually overheated I wasn't at lights or idling I was driving at 50-60km/h and the air was nice and cool outside.

Cheers

[l3004x4drifta]

give the hose a hard squeeze while the radiator cap is on. pressure should not be released. id replace the radiator cap anyway, just to rule that out.

[mstrrab1992]

My bad, not thermostat,thermo fan, and injectors may have shit in em put injector cleaner through, idk if it had like rust flake come through the lines into the injectors could be blocking them to a point where it runs to lean

[H8DAG8]

give the hose a hard squeeze while the radiator cap is on. pressure should not be released. id replace the radiator cap anyway, just to rule that out.

Radiator is now out to get a pressure test tomorrow - so can't check that at the mo! Radiator cap was replaced about 2 weeks ago too.

My bad, not thermostat,thermo fan, and injectors may have shit in em put injector cleaner through, idk if it had like rust flake come through the lines into the injectors could be blocking them to a point where it runs to lean

Haha sweet as, my fan measures longer than my 12" ruler, I'd say it's got a diameter of around 14-15". Also, the engine is carby so no injectors. Is there an easy way to clean the carb and all that that anyone knows of? Could the issue be in there? Ran fine with the same carb before the head was replaced.

[l3004x4drifta]

radiator cap replaced two weeks ago? did the troubles start around that time by any chance? im very suss on that.

[H8DAG8]

Can't completely remember but pretty sure the slight overheating (or hotter than usual) problem started well-before that.
It was a cap in an old box of new caps my grandad kept so I just used one and it fit perfect. Rubber seal was fine too.
Would it be worth me going to Repco or Supercheap and getting a cap from there specifically for my car? Knowing those shops they'll probably be $50 for a friggin cap!

[l3004x4drifta]

yeah. you need one that is specific to your engine/application. and no it shouldnt be too expensive. i cant imagine it costing more than say $20 bucks. and thats alot less than a new head and/or engine rebuild..

[mstrrab1992]

Try dif rad cap mite be it.

[81GL]

have the car sitting in a driveway or what ever, take the radiator cap off, start it up and leave it there idling until it is up to temperature. Confirm you have coolant movement through the radiator.

[H8DAG8]

yeah. you need one that is specific to your engine/application. and no it shouldnt be too expensive. i cant imagine it costing more than say $20 bucks. and thats alot less than a new head and/or engine rebuild..

Try dif rad cap mite be it.

Ok cool I'll get a new radiator cap tomorrow before I get the radiator pressure tested (may as well do that too, found a place that'll do it for free).
And yea tell me about it - had the old head crack on me due to age, and after I replaced that found that the balance shaft belt had snapped so had to go through the whole de-balancing job n then new cambelt n tensioner n everything else! Pretty much everything is new! Should have just V8'd the darn thing haha, if only I'd realised the head AND block were going to need work, wouldn't have been too much more $$ either!

Will post up how I get on tomorrow with the pressure test. If it's fine I'll put the new cap on and start it up and take it for a drive and keep a constant eye on the temp to see if she still overheats.

Just a question, if this cap is "wrong" what causes it to overheat?

have the car sitting in a driveway or what ever, take the radiator cap off, start it up and leave it there idling until it is up to temperature. Confirm you have coolant movement through the radiator.

Ok, I'll do that tomorrow before (or as) the test drive. So when I re-fill the radiator with water and coolant, and then leave it there idling without the cap on until it's up to temp, how do I confirm I've got coolant movement through the radiator??

[81GL]

Well with the radiator cap off, you can look into the radiator, should see the coolant moving

[H8DAG8]

Well with the radiator cap off, you can look into the radiator, should see the coolant moving

No other way of knowing? Due to my engine being de-balanced (i.e. no balance shafts) and having a lumpy cam the engine and car shake a fair bit so I assume it'll be quite hard to tell..

[l3004x4drifta]

the cap increases the boiling temperature of your coolant by about 25 degrees(when working correctly). why is this so? its a science type thingy.. (kinda like a pressure cooker uses temp and pressure to cook extra fast!) your pressure gets to a determined psi/kpa level(as indicated on the cap), and then vents into the over flow tank(make sure this is at the correct level also, as coolant also flows back). if you have a cap that is wrong, the system wont work correctly. i havent explained it aswell as id have liked.. but i hoped it has helped. talk to the guys at the place doing your pressure testing, but be careful they dont just want to sell you a new radiator! eg." would you like that free radiator check now sir?" $$$

[H8DAG8]

Yea sweet as mate I get you now. Will get onto that cap that's for my car tomorrow, the only thing is bloody Repco and Supercheap's systems don't list 4g63 engines under my model Sigma so it takes an age to get them to understand what engine I'm actually talking about (because of course they're all experts).

Hopefully the pressure test comes back fine, and if it does I'll get that cap and fire her up tomorrow and let her sit there and watch what the temp needle does.

Will post up if it's still over heating.

Cheers

[astronturbo77]

faulty thermostat or blocked radiator

[H8DAG8]

faulty thermostat or blocked radiator

As stated above thermostat was tested and works fine, it's brand new.
Also, radiator doesn't seem to be blocked as water flows through it both ways fine.
I assume a pressure test would also show if the radiator is blocked?

Cheers

[mstrrab1992]

faulty thermostat or blocked radiator

Use ur eyes....
Obviously sometimes people miss thing. just people in power doin as they please.

[robbert]

Take your radiator cap off and stick a coke bottle filled with water upside down in the radiator, so it's free standing. Then start your car and run till it's hot. Check for air bubbles going into the bottle. Even tho a new head gasket, it could be leaking again, or a crack.