My Kingdom for anyone who can solve overheat problem I’ve had for years!

For years I’ve had an ongoing overheat problem that miraculously cures itself but returns to haunt me again roughly once a month.

The temp needle generally sits at halfway (12 o’clock) position but sometimes it creeps close to the overheat and sits there for a while before eventually returning to the normal 12 o’clock position.  However, sometimes it swings fully over into the overheat and I instantly stop while it gurgles and cools.  Strangely no overflow water visible.  On these occasions the electric fan doesn’t kick in as the bottom hose is cold so doesn’t trip the fan sensor located on this hose.  I’ve changed the radiator, hoses, thermostat (many times), water pump and still the problem periodically persists!

When overheating I notice the expansion reservoir is full to the brim. But once cooled it returns to normal level with no water lost in the system!  I can then drive off and everything is fine for the next few hundred miles!  Can’t be leaking/blown head gasket as engine has run fine for years with no white smoke, spitting water/oil from exhaust.  No foam/oil in coolant.  When coolant changed no gunge in old water.

Any ideas on this persistent fault that can’t seem to be fixed?  Chris

Hi Gee. From your description of the symptoms it is classic faulty Thermostat. I realize that you have changed the thermostat several times but are you using a DECENT Thermostat??

The Dumpy First Line style Thermostats are usually the culprits. Normally the Original Equipment style Thermostat is the better one to buy from Nippart or Blue Line although usually around £25 a time for Nippart and a good bit more for Blue Line - I find them the most reliable.

Shop around on Ebay. Price ranges up and down wildly on there as we all know but I would always go for a Blue Line.

I have a few Nipparts stats available, and from (very recent) experience I agree with Woodie's diagnosis. You are fitting it with the jiggle-pin at the top, I hope?

Thanks chaps for you thoughts. I can't recall the make of the three thermostats used (I've changed two and a garage one).  On removal I've checked the old one in hot water and they open at the correct temperature.  I've been religious about checking the jiggle-pin is in the correct position.

As you know changing the thermostat requires removal of seats, central handbrake/gear stick divider and awkward to locate thermostat bolts - so don't want to unnecessarily tackle again.  However, if this fixes it then certainly worth the trouble (and half my Kingdom).  

I've changed thermostats on previous old vechicles (that literally took 5 mins) and replacements always did the job straight away.  Is the Hijet that more critical?  I feel you both are talking from previous experience? Thanks again guys. Chris

Your problem is intermittant, so what could vary? The stat could occasionally be getting stuck. Is there anything that happens shortly before you overheat, i.e. is it soon after you top up the coolant or something else? Something must be causing it - probably the same thing each time - it's just a matter of finding what. If it's not had a pair of new rad caps for a while I'd change them just in case.
I found I only needed to remove the passenger seat to do the stat. How much is your kingdom worth, anyway?

As well as changing the rad caps make sure the rad cap sealing face inside is in good condition. No point haveing a new cap if the face is corroded. Either use emery cloth or I did use a tap face cleaning tool to good effect on mine, just don’t be too aggressive as it’s not that thick.
What about coolant? I hope you are using the correct coolant and not just topping up with plain water each time as that will have an effect on when the water boils etc.

Yes, new radiator caps fitted.  Proper coolant mix used each change.

I can't find a pattern to the overheating!  I've had the problem years covering different weather and conditions.  It's not related to topping up coolant etc.  Sometimes it runs normally for hours (temp needle 12 o'clock), then the needle suddenly moves closer to overheat position telling me the bottom hose is not circulating. Unless I stop or very slow traffic the needle doesn't enter the overheat and continues to drive okay.  Then later on the same trip the needle can suddenly return to the normal 12 o'clock position.

Sometimes, like yesterday morning, it went up directly to the close to overheat position after just 3 miles!  Reusing the van later that same day it ran normal temperature for the whole afternoon with hot bottom hose kicking in electric fan as normal when stopping or hitting slow traffic!

Could a series of 3 replacement thermostats all be faulty?  (Those replaced opened okay in hot water saucepan test).  Thanks again forum for your thoughts.  Chris

g149 wrote:Could a series of 3 replacement thermostats all be faulty?

Does seem unlikely, but the symptoms do sound like an occasionally-sticking stat. They might open OK in the pan, but how many times did you try them?

You could always get one of those cheap car outside thermometers and tape the sensor to the bottom hose to give you a real-time temp readout, perhaps.

Of course it might even be the sender or gauge playing up intermittantly, that would be really weird!

Thanks PFM.  Maybe worth changing thermostat yet again for a reputable replacement!  

I have in the past changed the temp sender.  I think the gauge is working fine for when it starts to climb if I check the bottom hose I find it cold/tepid which without proper circulation would push up the temp.

Value your thoughts forum.  Chris

i am no mechanic but what if, for instance, there is a moving airlock that gets passed around when it overheats??
Probably daft but....

did you make sure you bled the coolant accordingly....?

Have you done an engine cooling system flush to make sure it’s not crud restricting flow through rad?

Raggy wrote:As well as changing the rad caps make sure the rad cap sealing face inside is in good condition. No point haveing a new cap if the face is corroded. ...

UPDATE:  My garage mechanic recently noticed scale on the ring where the radiator cap (from expansion reservoir) sits and smoothed it out.  He believed that is was causing pressure/coolant expansion imbalances and sucking in steam air locks. (Coolant level under rad cap fed from expansion reservoir is always very low or even empty in that hose).  Usually little more than a cup full or water will top it up.  However, problem persists as before!

HERE IS FULL SUMMARY OF PERIODIC OVERHEATING (using LPG or petrol) – DAIHATSU HIJET 2005

Fault:  For years I’ve had an overheating issue.  It used to occur once in a blue moon but is now more regular - about a third of the time.
When driving the temperature gauge normally stays at mid 12 o’ clock position.  However, sometimes it rises and settles at the ¾ position nearing overheat.  After a period in this position it often will return back to the normal 12 o’ clock position.  However, occasionally it won’t and the needle will enter the overheat position.  At this point I stop.  After 15 mins of the engine cooling I remove the radiator cap fed by the reservoir (not the main front radiator cap) and notice it very low or even empty in that hose.  Usually little more than a cup full or water will top it up.   I can restart the engine and the vehicle will drive off with temp gauge back to normal (even for another 200 miles).  The engine always purrs fine with no misfiring.  On very rare occasions when I’ve not noticed the temp gauge move into the red it has overheated with water escaping and accompanying hisses and gurgles.

When the temp needle is at normal 12 o’clock position the bottom hose feeding the main radiator is always hot.  When then idling in slow traffic the temp will rise and the electric fan will kick in – it’s sensor in on that bottom hose.  When the temp gauge is at ¾ position the bottom hose is always cold and thus electric fan won’t kick in!

The problem has become more regular in recent months.  It can happen from cold within just 3 miles drive.  Yet after stopping for 10 minutes to cool and adding just a cup of water it will always drive off normally for many miles!  Yesterday the engine was running fine but after 10 mins stop at petrol station the temp gauge moved and settled at ¾ position.

The expansion tank has occasionally been full to the brim when problem develops.  But more often it just stays at the full level line whether hot or cold!  The front radiator is always full with no coolant loss.

Recent garage work:

My garage recently noticed scale on the ring where the radiator cap (from expansion reservoir) sits and smoothed it out.  They believed that is was causing pressure/coolant expansion imbalances and sucking in steam air locks.  But problem persists.

Three thermostats:  Opening temperature checked in situ using laser thermometer and opening fine.  Also, old ones checked and fine.  Earlier forum response was - "I realize that you have changed the thermostat several times but are you using a DECENT Thermostat??  The Dumpy First Line style Thermostats are usually the culprits.... "  Still haven't changed thermostat.

Coolant system flushed under pressure and correct coolant mix added in correct procedure.

New main radiator.

New radiator caps (both front radiator and cap by expansion tank)

Garage is adamant that it can’t be head gasket as no white smoke or exhaust spitting water/oil drops and no oiliness in coolant.  Engine always runs smoothly.

New hoses

Water pump was changed a number of years ago.

Temp gauge sender changed a number of years ago.

This puzzles me - it seems the system heats up and at some random point later:

g149 wrote:When the temp gauge is at ¾ position the bottom hose is always cold and thus electric fan won’t kick in!

How can this happen - surely the water pump can't work intermittantly?

g149 wrote:After 15 mins of the engine cooling I remove the radiator cap fed by the reservoir (not the main front radiator cap) and notice it very low or even empty in that hose.

I think that's too soon - I leave mine at least an hour before opening.

g149 wrote: The front radiator is always full with no coolant loss.

This too is strange - why doesn't the water in the rad circulate and take up the space in the bottom hose?

When I first refilled a 1.3 it was after I'd fitted a new rad. Blissfully ignoring the label by the rad I followed the 993 procedure and only filled through the rad, and only subsequently ever checked level and topped up at the rad. This was fine for a couple of years until recently when I started topping up under the seat as per instructions (after it started boiling frequently). I've now gone back to the 993 procedure and it's been better ever since, though still losing coolant, so I have another couple of rad caps on order.

Think the key statement is the one that says the tube under the rad cap gets empty, where is the coolant going? Solve that, solve the overheat issue. If the water isn’t being blown into the expansion bottle due to air getting in...where is it going? Is the sealing faces for the under engine rad cap in good condition and as PFM says, follow a good coolant bleed/filling regime.

Raggy wrote:Think the key statement is the one that says the tube under the rad cap gets empty, where is the coolant going? Solve that, solve the overheat issue. If the water isn’t being blown into the expansion bottle due to air getting in...where is it going? Is the sealing faces for the under engine rad cap in good condition and as PFM says, follow a good coolant bleed/filling regime. .....

To refill the hose under expansion rad cap is barely a cup full.  On the odd rare occasion the expansion tank has been full to the brim but not overflowed.  The garage was thorough in checking leaks with ultra-violet dye - leaking radiator and hoses changed.

My mechanic has suggested removing the thermostat till late autumn, then fit Nippart thermostat.  I'll do this myself to save money - the handbook/manual shows rough illustrations for this.  Do good instructions for an amateur exist anywhere?

Yes there is a post somewhere by HighlyJetted but I can't find it. Here's how I did it:

Drain system opening both rad caps and bleed valve (not LPG), remove passengers seat (I didn't see the need to remove driver's too), seatbelt stalks, handbrake plastic surround. Measure threaded length of handbrake cable after nuts, then remove cable, then wire for warning light from under handbrake, and the metal bridge with handbrake lever still on. Slacken alternator and take belt off.

Unclip small hose near rad-cap under seat. As t/stat cover is plastic and frail you might want to leave this attached to the housing. The large hose to the housing can be unclipped, loosened carefully using grips, then removed.

3 10mm bolts hold housing in place. I pre-sprayed mine with plus-gas and they undid easily after a tightening tweak. People say you need a 1/4" drive extension bar but I only have 3/8" and it's fine. You do need to unclip the black cable clip to gain access. Best to undo the bolts evenly. A light tap and my housing came free.

Refit t/stat with jiggle pin at top. Rubber ring is the gasket, but I did smear some hylomar just to be safe. Reassembly is the reverse, but TAKE CARE NOT TO OVERTIGHTEN the housing bolts. Torque is given in the manual as: Cover - Thermostat 5.9 ÷ 8.8 but my wrench won't go down that far! (those settings are a copy-and-paste)

FURTHER UPDATE:  Removed thermostat completely. Bottom hose now heats equally with top.  So when idling the sensor on bottom hose kicks in the electric fan.  Van runs fine with no thermostat though temp needle now hardly moves off cold position.  (Will fit new thermostat in the autumn).  

After driving 30 miles last night I noticed expansion tank was full to the brim (not overflowing).  The hose under top rad cap near expansion tank shows near empty but only takes a cup full to fill - not much.

I haven't done a coolant change for a while and removed a small rubber cap over a tiny protruding pipe besides first spark plug, expecting this might be an engine coolant outlet?  No coolant flowed from it when refilling or with the engine running hot.  Could someone tell me it's purpose please?

g149 wrote: Van runs fine with no thermostat though temp needle now hardly moves off cold position.

That's interesting, might be the reason one of mine runs like that. Glad you're making some progress.

WHAT IS THIS? (image may not be showing - but it's a tiny upright protruding pipe besides first spark plug with small rubber cap.

I haven't done a coolant change for a while and removed the small rubber cap over a tiny protruding pipe besides first spark plug, expecting this might be an engine coolant outlet?  No coolant flowed from it when refilling or with the engine running hot.  Could someone tell me it's purpose please?

WHAT'S THIS?  Try this link  
https://drive.google.com/file/d/1KFO2-DO2jCJ9hQ9L9tquZA4vZXH2qqYM/view

Removing thermostat hasn't stopped overheating problem after all!  On longish runs the temp gauge rises as before.  On directly inspecting I find the expansion tank actually overflowing and when cooled doesn't seem to suck it back with usual cup full missing from top hose.  The bottom hose gets hot but when squeezed doesn't feel it has water in it. My mechanic says it fills with steam and thus doesn't trigger the electric fan correctly.  So far no holidays this summer in my Hijet Romahome Camper!

It’s definately getting air in somewhere and pressurising it! That’s how it is blowing the water into the overflow tank. So it’s a leak somewhere, either air getting past a clip or a seeping pipe (which is air being sucked in and as yours is not sucking the fluid back in I don’t think so, and higher pressure inside would show up as leaks which you have not seen)a leak on the cylinder head/gasket (high pressure cylinder pressure forcing air into waterway at some point). Now if the rad cap is the correct one (0.9bar) and the sealing face is good, it should hold the correct pressure and seal correctly to that pressure. So I am afraid I would put money on the head/head gasket failure but make sure that rad cap and sealing face are in good condition first.

Raggy wrote:...So I am afraid I would put money on the head/head gasket failure but make sure that rad cap and sealing face are in good condition first.

So what is the best way to test for that fault?  Would it be a head cylinder compression test?  There are self tester kits available from Halfords around £30 or would it need a more comprehensive test done at a specialist?  If "sealing face" on rad cap near expansion tank (main radiator is brand new) which has been cleaned and scale removed; can that metal pipe be bought anywhere?

My garage has been adamant it's not a head gasket as smooth engine performance, no white smoke, no oiliness in coolant - so they've said no need for a compression test!

Hi. I'm new to this forum and just searching for the answer for the same overheating problem with my daughter's '93 HiJet. And reading the posts I've realized that if the problem persists even taking away the thermostat, there's an air bubble somewhere in the circuit. I changed some of the hoses and I realize now that the one that runs from the thermostat to the cylinder head (small diameter) is a little longer than necessary and a part of it is a little over the level of the refilling cap, so there's no chance for the air to get out from there. When that air trapped on the hose moves and gets to the pump, water circulation stops, because the pump is not designed to move air, just water. I'll fix that hose tomorrow, test the van for a few days and bring the answer back. I don't know if g149 has solved the problem or dynamited his hyjet but I leave here a new 'theory' on this thread. Please check the level of the hoses respect the filling cap. Regards.

Sorry Luigi but your theory is an old one and nothing to do with either the water pump or the pipe being above the Radiator Filler Cap Level.
The problem always is that garages, Hi-Jet Owners do not bleed the whole system properly. The Heater Matrix is well above the Radiator Filler Cap and if you don't bleed the air out of the Heater Matrix under water pressure with a Watering Can and hose into your Radiator neck and out of the bleed nipple on the bulkhead above the Radiator then you will never stop it overheating.

I have covered this matter so many times now, Raggy has gone over my filling process and several others have copied my guidelines.

Any air left in the Heater Matrix will expand far more than water so it will build up pressure and push the water out of the Radiator Cap either under the seat or on the Radiator. The Rad Caps need to be in as new condition and the seating in the neck of the metal pipe with the Rad Cap on under the seat must be absolutely smooth. You can clean in up with a plumbers Seat Cutter Tool. Same for the Radiator Seat if you have a metal radiator still. Once you are sure that
the seats are absolutely flat then fit 2 new Radiator Caps. They are cheap enough and so many times are the main cause of Overheating and Water loss into the Expansion Tank or out of the Radiator.

Ok, Woodie. Finally we followed Raggys (or yours) set of instructions and it worked perfectly well. So the only thing I can say is Thank You!!!

Luigi - you are a GENTLEMAN SIR. Thank you very much for saying thank you and I am genuinely pleased that it has done the trick for you.

It's nice to know that OCCASIONALLY someone does take some notice of this INSOMNIAL OLD FART and take the time to say thank you. You are very definitely on the top end of my WHITE LIST of members that I am happy to help out. You would be surprised just how few Members bother to say thank you - or let me know that a spare part has arrived safely or that it has done the trick. But I do have a core of regular Members who always say thank you for the time I take to write a helpful reply or take or make a phone call - - - and they know who they are and that I really appreciate their thoughtfulness.
THANK YOU VERY MUCH AGAIN. Woody.

Just one thing though Luigi - - Get to bed earlier or you will end up an INSOMNIAC like me.

All thanks go to Woodie, I just listed out his instructions