Poor Acceleration?

[snailslime]

Hi everyone

I took my mk1 out for a long drive today (about 150 miles) & i had no problems whatsoever for most of the journey, that is until I was nearing home and the temperature gauge started reading a bit higher than usual ( 3/4 rather than the normal 1/2 way across). I stopped at some traffic lights, then when i pulled away the acceleration became very slow!

It stayed this way until i got home, where i opened the engine lid up & the expansion tank was bubbling and the lid had melted slightly!! It sounded like a kettle thats boiling!!

After leaving the car for a while to cool down, all seemed to be back to normal! But then after a while the acceleration was poor once again and the temp reading was 3/4 the way across the dial again too.

I have no idea how to solve this so am wondering if this has happened to anyone else before? and more importantly, how is it fixed?

My only guess is the thermostat being faulty. but would this cause the engine to go slower?! Any suggestions would be greatly appreciated.

[THE DUKE]

Head Gasket?? Water temp sender??

Lost water?
Temps High?
Poor performance?

[The TVIS Kid]

Sounds more like a blockage than a knackered thermostat as it is rare they get stuck closed (more likely to get stuck open). If you radiator is cold or only luke warm then the thermostate might be shot I would suggest you bleed the system and flush it that way you can see whats wrong as you can send water down the different pipes seperatley.

If your engine cooks then it will definatly affect your cars performance as it won't be cooled down, i would suggest you don't run it when it gets hot until you solve the problem.

Also, is your engine fan on? this should help cool things down, if not then you may have a electrical fault.

Is there water in the oil or mayo type substance where you fill with oil? Thats a good sign your head gaskets gone.

[snailslime]

Have had a look in the expansion tank, no oil there.
Have removed oil filler cap, no white froth in there.
The engine bay fan comes on ok.

[THE DUKE]

lost any water? engine light come on?

[snailslime]

No, coolant level not moved and no warning lights come on.

[THE DUKE]

would start with a stuck stat and coolant bleed..

[snailslime]

Ok, thanks for the advice.
Will flush the cooling system and replace the thermostat.
Would this really cause the car to accelerate slowly?

[THE DUKE]

yeah normally if cars overheat (and are clever enough) the ecu cuts ignition and fueling. I'd say try removing stat and see what happens from there

[snailslime]

Will do, cheers!

I'll post the results when i've tried it.

[widster]

My friends MR2 (G reg T-Bar) had the same symptoms as yours. A mechanic came out and diagnosed cylinder head gasket but all it needed was a new thermostat and new coolant as it hadn't been changed for a while by previous owner.

[luthor1]

check you haven't got a tiny stone in your radiator on your long run. This could cause air to get into the system. Basically what everyone is saying.

I would empty the whole system, change the thermostat and radiator cap, and then have the system high-pressure tested. Then refill.

Head gasket replacement is an excellent excuse the cylinder head work by the way!

[Lunarmatic]

No, coolant level not moved and no warning lights come on.

Sorry if you already know this but did you check that the coolant level is up to the filler neck under the pressure cap (rather than just looking at the level in the expansion tank)?

Reason I ask is that you can be losing coolant even though the expansion tank level will remain the same.

If there is any coolant loss then it means air will be getting into the system. This will cause the temp guage to go all over the place as the air passes the temp sender and I think this will, in turn, upset the ECU. Eventually you'll get enough air in the system to get an airlock that will stop the coolant getting to the radiator and then the engine will start to cook.

[snailslime]

Ok, i have just had the water filler cap off and there was only a very shallow bit of water at the bottom of the pipe! Didnt take this off before as the engine was too hot. So i guess that air block is the cause. The level in the expansion tank was higher also (Thanks lunarmatic)

Am going to flush out the system after work tonight and put in new coolant and thermostat and a new radiator cap just for good measure!
Any suggestions on getting all the air out of the system when i refill?

[The TVIS Kid]

Remember if you fully fluch the system it will take about 12 ltrs of fluid so you need to buy more than one 5ltr coolant bottle. I put 7 lttrs of coolant and the rest water.

Also when you have filled it run the enigine until hot (so the thermostat opens) and then take the filler cap off to let the air escape (or else you will get air trapped in the system and ur idle speed will be lumpy). Let the engine cool and top up as required, don't put cold water in a hot engine.

You will probably have to do this a few times to get all the air out.

[LimeyMk1]

Also when you have filled it run the enigine until hot (so the thermostat opens) and then take the filler cap off to let the air escape (or else you will get air trapped in the system and ur idle speed will be lumpy).

That's a bit dangerous isn't it? The best way AFAIK is to put the pressure cap on but only turn it 90 degrees (1ST notch) and run the engine up to temperature. This will prevent pressure build up and let the air out but the coolant will still circulate.

[HT]

Remember if you fully fluch the system it will take about 12 ltrs of fluid so you need to buy more than one 5ltr coolant bottle. I put 7 lttrs of coolant and the rest water.

Also when you have filled it run the enigine until hot (so the thermostat opens) and then take the filler cap off to let the air escape (or else you will get air trapped in the system and ur idle speed will be lumpy). Let the engine cool and top up as required, don't put cold water in a hot engine.

You will probably have to do this a few times to get all the air out.

Total coolant capacity is 12litres, however you'll be doing well to empty the system completely - therefore probably won't need the full 12 litres when refilling time comes.

Regarding refilling consult your owners manual regarding bleeding - if not this is loosely the proceedure.

Before you do make sure the car is on a level site, with the heater fully on the hot position, and fill the expansion tank to the max, then:

Locate & open; the engine bay bleed valve by the thermostat housing, one by the side of the raditor towards the top, and a further one off the water heating valve - located in the front boot, on the bulkhead, beneath the plastic cover. The last two require the fitting of the clear tubes that should be stored beneath the said plastic cover (if not present seek two metre plus lengths of 1/4" (I think) tubing to act as vent pipes). Fit 'bleed pipes' to heater valve & raditor and secure in upright position (tape etc) then open all the bleed vales.

Start filling closing the thermostat one off when you get continuos stream of water withotu air bubbles form it. Then keep filling unitl the two bleed pipes (at the front of the car) coolant level is level with fillerin the engine bay. Close off the bleed valves and put the pressure cap back ont he filler but don't fully tighten. run the engine until its warm, stop allow it to cool enough to check then top up if need be then fully retighten (you may need to do this more than once). HTH

[jimi]

I've always bled mine as above except I have the back of the car higher than the front, I found this helps and never had a problem bleeding since I started doing this.
hth
Jimi

[snailslime]

Thanks for all your advice

My haynes manual gives a good walk through on draining/flushing/refilling the system, pretty much as HT says to do it.

Will raise the car from the back as well as you advise Jimi, Cheers!

[HT]

Oops forgot that jimi - and it does make a fair bit of difference - unless you do as a friend once did and jacked the front up!!