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mgf
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Discussion Starter #1
hi everyone,

can i ask for advice on the issue i have with my 1999 mark 2 mgf mpi with running too hot sometimes.

just bought it privately, 60,000 miles, 1.8 mpi, last owner had it ten years, its been well looked after, head was done 4 years ago, new rad, stainless steel water pipes etc.

anyway when i went to view it, drove it , checked everything, all good, drove it home the following week on the hottest day of the year in rush hour about 50 miles all good ran perfectly, drove it around the town that night same perfect, 2 days later took it for drive temperature gauge went right up and started to blow steam from expansion, stopped and waited for it to cool, topped it up with about 1 litre of water and drove it home.

investigation - car idles fine, doesnt over heat if idling, after it did overheat initially i noticed radiator fan didnt come over so did the usual test disconnecting the temp sensor to test fan and it came on so fan is good, then i changed the thermostat and put in one with jiggle valve and then new inlet manifold gasket along with cleaning the inlet manifold jiggle valve. topped up with 50% oat coolant and ran the car over a few weeks just short trips but still noticed sometimes the temp starts to go up until i turn the heater fan on full then it cools down, fan at front on radiator kicks in aswell. oil is clean, not loosing any coolant, no smoke.

i have noticed i have no return flow to header tank what so ever, reading the forums there are 2 jiggle valves, one on the inlet manifold i cleaned and one of the passenger side on the engine which i havent looked at yet which i am aiming to look at tonight.

i am confused as i understood the jiggle valves are there to let any air out of the system/head, i dont think they are there to return a small flow of coolant to the header tank but looking at the cooling system diagrams they all show hot coolant returning to the header tank and other users on the forums also say there should be a return flow which i do not have.

anyone have any clues? could it be the waterpump?

thanks
martin
 

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hi everyone,

can i ask for advice on the issue i have with my 1999 mark 2 mgf mpi with running too hot sometimes.

just bought it privately, 60,000 miles, 1.8 mpi, last owner had it ten years, its been well looked after, head was done 4 years ago, new rad, stainless steel water pipes etc.

anyway when i went to view it, drove it , checked everything, all good, drove it home the following week on the hottest day of the year in rush hour about 50 miles all good ran perfectly, drove it around the town that night same perfect, 2 days later took it for drive temperature gauge went right up and started to blow steam from expansion, stopped and waited for it to cool, topped it up with about 1 litre of water and drove it home.

investigation - car idles fine, doesnt over heat if idling, after it did overheat initially i noticed radiator fan didnt come over so did the usual test disconnecting the temp sensor to test fan and it came on so fan is good, then i changed the thermostat and put in one with jiggle valve and then new inlet manifold gasket along with cleaning the inlet manifold jiggle valve. topped up with 50% oat coolant and ran the car over a few weeks just short trips but still noticed sometimes the temp starts to go up until i turn the heater fan on full then it cools down, fan at front on radiator kicks in aswell. oil is clean, not loosing any coolant, no smoke.

i have noticed i have no return flow to header tank what so ever, reading the forums there are 2 jiggle valves, one on the inlet manifold i cleaned and one of the passenger side on the engine which i havent looked at yet which i am aiming to look at tonight.

i am confused as i understood the jiggle valves are there to let any air out of the system/head, i dont think they are there to return a small flow of coolant to the header tank but looking at the cooling system diagrams they all show hot coolant returning to the header tank and other users on the forums also say there should be a return flow which i do not have.

anyone have any clues? could it be the waterpump?

thanks
martin
Once bled properly, that should be it. Normally if the system has not been bled correctly, when moving the temp stays normal but when idling, then the cap will start to blow to release pressure. You do not have these symptoms.

The temp should not change whether the heating is on and off in my experience.

The lack of return flow is not right as you have identified. There should be a strong flow whether the expansion cap is off or on.

I have not known a waterpump to fail other than it can leak - always possible I guess.

II would do four things:

1. Check that the pipes are correctly routed especially the inflow and outflow pipes connected to the heater. They sometimes get interchanged at the back of the engine (I do not know it anyone has been messing about with the pipes). This happened to me once when work was done by a garage. It caused all sorts of cooling problems which I sorted out at home.

2. Totally flush the cooling system

3. Re-bleed the system using ALL three bleed points (engine, heater and radiator) with the expansion cap OFF. The jiggle valve is to displace any air trapped at that point in the cooling system.

4. Replace cap. Cheap so do it as insurance.

In my experience, if the correct bleed procedure is undertaken, there will be no problems.

On the water pump, do you know when it was last replaced?

Best of luck.
 

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mgf
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Discussion Starter #4
Once bled properly, that should be it. Normally if the system has not been bled correctly, when moving the temp stays normal but when idling, then the cap will start to blow to release pressure. You do not have these symptoms.

The temp should not change whether the heating is on and off in my experience.

The lack of return flow is not right as you have identified. There should be a strong flow whether the expansion cap is off or on.

I have not known a waterpump to fail other than it can leak - always possible I guess.

II would do four things:

1. Check that the pipes are correctly routed especially the inflow and outflow pipes connected to the heater. They sometimes get interchanged at the back of the engine (I do not know it anyone has been messing about with the pipes). This happened to me once when work was done by a garage. It caused all sorts of cooling problems which I sorted out at home.

2. Totally flush the cooling system

3. Re-bleed the system using ALL three bleed points (engine, heater and radiator) with the expansion cap OFF. The jiggle valve is to displace any air trapped at that point in the cooling system.

4. Replace cap. Cheap so do it as insurance.

In my experience, if the correct bleed procedure is undertaken, there will be no problems.

On the water pump, do you know when it was last replaced?

Best of luck.
hi everyone,
thanks for the advice.

i did put a new expansion cap on but that made no difference but it looks like the problem is now solved as the jiggle valve near the distributor side of the engine i took apart and it was completely clogged up that no air or water could get past which i expect left a very large air lock. i now get plenty of flow back to the expansion tank and the temp needle doesnt move at all once it hits about 8 o clock on the gauge.

had the car 6 weeks and now i can drive it so am very happy.

cheers everyone.
 

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mgf
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Discussion Starter #5
hi everyone

thought it was fixed, took mgf for two 20 mile return trips on saturday around kent area mainly country roads car run fine, then on the final return journey about 1 mile from home temperature gauge started its old trick of moving up to 3/4 so pulled over turned engine off, header tank hadnt errupted but could see movement/bubbling. checked underneath and the return from the radiator (bottom driver side hose) was cold.

once home and cooled, checked for air in all the 3 bleed valves didnt seem to find any so at a loss again to what is causing it.

on a side note when i clean the clogged up jiggle valve on distributor side last week it was clogged full with a pink paper like substance. i know the previous owner said he had the car flushed end of june for MOT so wondering if there is more of this paper like substance in the system. it has brand new rad and stainless steel pipes.

next plan might be to remove all the hoses and check for blockages. also read on the forums air could be getting in someone.

read similar issues on forums but no answers, confused how i can drive the car almost 40 miles with variety of driving, stopping, queuing at traffic etc and also can leave it idling and everyone seems ok but just cant trust the car as i know at some point it will start to over heat.
 

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mg_tf
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Hi, sorry to hear that you are still having issues. Just a point I picked up in your post. I noted that you refer to the return hose from the radiator on the driver side as “the bottom hose”. Not sure if the MGF is different to my MG TF but on my car the return hose from the radiator exits from the top of the radiator on the drivers side. The inlet hose to the rad enters the rad at the bottom on the passenger side.
 

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Forgot to add, you didn’t mention whether the inlet hose to the rad was hot/cold when you checked the return hose? Have you checked the thermostat?
 

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My TF started 'overheating' and coolant bubbling recently 2 yrs after a HG replacement, depends on your gauge as it as we know an 'indication' but given you drove and allowed the needle to get over the halfway not to mention three quarters (!) I would think that if you did not have HGF you will have now; in my experience the engine just cannot take such 'high' temps and 'survive' get the £200-400 ready for a HG replacement. I had mine done along with the pump and cam belt and the car is running noticeably better and cooler. The coolant leak I was experiencing and topping-up which I had convinced myself was the pump was in fact on the HG leaking coolant in the location above the waterpump; all became clear when the Head was lifted. Not sure why it went I have had the K series long enough and care for them, possibly a **** job when it was done.
 

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mgf
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Discussion Starter #9
98luke - the radiator pipe returning to the engine you are correct it at the top, sorry should have mentioned i took the under bonnet plastic cover off that covers the bleed need for the heater, if you take that off you can see straight down to the road and easily bend down and touch both inlet and outlet coolant pipes to the rad. inlet was hot and the outlet which is the far side hose was cold.

i have changed the thermostat and expansion cap the week after it first got hot and started to boil. the thermostat was working i tested in a sauce pan along with a new one and the old one was slow to open compared to the near one, it also had alot of debris on the old one. new thermostat is 88c opening, i did see a chap on you tube who put a 82c thermostat in but he didnt say where he sourced it from just that it was a bugger to find, i think its a mini 1275gt thermostat?

flanners - when the temp starts to rise its very quick, under 10 seconds from one notch under normal to 3/4 , since the first overheating i glance at the temp gauge every 5 seconds so when i saw it start to move i pulled over straight away and turned the engine off.

i have attached photo of the jiggle valve i cleaned last week that was completely blocked with a paper like substance. my MOT garage who i trust explicitly for the last 20 years seem to think its a leak sealant of some sort but not one of those head gasket repair liquids and they also think its a blockage, think this substance could be all around the system and maybe degrading the water pump impellors.

did your tf has intermittant overheating like mine or wasnt it just overheating every time you drove it?

both you of thank you for your advice.
 

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Ok, if the inlet hose to the Radiator is hot and the outlet is cold, would that not suggest a problem with the radiator also? Sounds like the gunk that you found in the jiggle valve may be clogging your radiator also. Maybe a thorough flush is required.

FYI, I have fitted an 82c thermostat, but I have relocated my thermostat to the inlet hose of the radiator. This allows a greater volume of water to circulate around the engine circuit before the thermostat opens and less likely to thermally shock the engine. Because the stat is now further away from its original position, the lower temp stat helps.

I believe that I bought the 82c stat from Rimmer Brothers.
 

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mgf
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Discussion Starter #12
hi Luke

the radiator is brand new, the previous owner said the system was flushed for the mot in july about 1 month before i bought the car, there is no way the flush would have got that paper debris out as i had to dig at it with a flat bladed screw driver as it was compressed so much the ball bearing didnt move, i spoke to rimmers the day after the issue started and ask them if they had an 82c degrees thermostat and they said no. i think i ebayed and saw that the classic mini is 82c just not sure its correct size as i remember there is a few mms difference in height.

i think next job as soon as i can get the mg in my garage (full of junk at moment) is to drain coolant, flush again assuming the other chap did do it, also i think i might have to take a look at water pump, oh and i will remove all the hoses and check them.

a prt thermostat is on my future job list i think to as you say limit the thermal shock.

i also ran the car idling and revving as well with the heater control in off until i heard the radiator fan come on , did this a few times on sunday to check the hoses in and out of radiator making sure they were both hot. fan kicks in and cools the coolant down as expected.

cheers martin
 

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Hello Martin,
Your indicated fluctuating overheating via. reading the gauge may well be correct, but I would have thought it worth checking the coolant temperature via. live data when the car is actually on the road and showing an indicated overheating.
Could eliminate a faulty temperature gauge sender.
 

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mgf
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Hi Martin,

It does sounds like there is some sort of radiator leak sealant in the system. You mentioned that the radiator is new but it could be that the paper-like sealant is blocking some amount of flow through your new radiator as well.

It might be worthwhile checking the temperature of different coolant hoses while the car is running with an infrared temperature gun to see if there are more than just the one return hose from the radiator that are not getting hot, or not as hot as they should get. If possible, you might want to check to see if there are cool spots in the radiator due to plugging from the paper substance. I'd also suggest that when you do another flush, that you disconnect the radiator from the system and do a reverse flush through the radiator, trying to push the paper substance back out of the radiator from the direction it came into the radiator.

Mark
 

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mgf
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Discussion Starter #17
82c degrees thermo is on its way from rimmers, also purchased bluetooth odb2 reader so i can see the live temp, hopefully weekend i will get thermo in, i will also take all the hose off and check for debris and will also take radiator off and get the hosepipe thru it.

will update once done.

thanks everyone, advice is very appreciated.
martin
 

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mgf
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Discussion Starter #18
Hi Luke

did the thermostat gts101 need modification to fit your mgf? this only just fits in the thermo housing if you leave out the rubber o ring but i am concerned about expansion?

thanks
martin
 

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mgf
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Discussion Starter #20
hi Luke

the new one is alot longer, the lower metal disk catches on the plastic thermostat housing, do you have the normal thermostat housing or PRT system? if you have the normal thermostat housing did you fit the rubber o ring around the thermostat? if i fit the o ring on the gts101 thermostat from rimmers the housing will not join together.

thanks
martin
 
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