JJC Posted June 12, 2020 Report Share Posted June 12, 2020 Suggestions welcome. I’ve tried all the obvious things. In the garage it sits there and barely comes up to temp. But on the road after about 5 minutes temperature goes off the end. Electric fan kicks in but doesn’t cope. It’s not the thermostat, water pump, radiator. Before replacing FO8 gaskets it worked fine. So I don’t think it’s modern thermostat/bypass hose thing. And yes the fan does blow the right way. JJC Quote Link to post Share on other sites
stuart Posted June 12, 2020 Report Share Posted June 12, 2020 (edited) Possible airlock, timing, mixture, water pump impeller broken Stuart. Edited June 12, 2020 by stuart Quote Link to post Share on other sites
RogerH Posted June 12, 2020 Report Share Posted June 12, 2020 Hi JJC, the engine will be using/ more power when driving than simply sitting - even at the same rpm. So assuming all the indications are about correct then perhaps it is the engine that is generating this extra heat. What is your timing like? What is your mixture like? An weak, mixture with advanced spark will make more heat than a rich/retarded combination. Roger Quote Link to post Share on other sites
JJC Posted June 12, 2020 Author Report Share Posted June 12, 2020 ŶThanks Stuart and Roger. Timing accurate, mixture slightly rich, water pump fine (I took it off!), thermostat fine. Where would an air lock sit? JJC Quote Link to post Share on other sites
Z320 Posted June 12, 2020 Report Share Posted June 12, 2020 hi jjc, you had the thermostat out and you see some millimeters coolant in the rad and also in the opened thermostat housing? Then the water pump is below the coolant level and when it starts spinning there is no air trapped anywhere. This pump is a M-O-N-S-T-E-R and not a toy pump like in your house central heating. It smashes the air out and keeps it in the flow Ciao, Marco Quote Link to post Share on other sites
JJC Posted June 12, 2020 Author Report Share Posted June 12, 2020 Marco. Yes, current thinking is an air lock. So put it back together and hope? JJC Quote Link to post Share on other sites
stillp Posted June 12, 2020 Report Share Posted June 12, 2020 Does it push water into the overflow bottle when hot and suck it back as it cools? Pete Quote Link to post Share on other sites
Z320 Posted June 12, 2020 Report Share Posted June 12, 2020 You tell "the temperature goes off the end". Don't be angry with me, but is not very much information for us. It could be useful to tell us more. Quote Link to post Share on other sites
BlueTR3A-5EKT Posted June 12, 2020 Report Share Posted June 12, 2020 4 hours ago, JJC said: Suggestions welcome. I’ve tried all the obvious things. In the garage it sits there and barely comes up to temp. But on the road after about 5 minutes temperature goes off the end. Electric fan kicks in but doesn’t cope. It’s not the thermostat, water pump, radiator. Before replacing FO8 gaskets it worked fine. So I don’t think it’s modern thermostat/bypass hose thing. And yes the fan does blow the right way. JJC When did you replace the Fig 8 seals ? Has the head been re-torqued since then? Have you 'burped' the middle radiator hose? - squeeze the middle hose with the radiator cap off a few times to try to expel any trapped air. Worth doing when the engine is ticking over but keep hands clear of the rotating bits. If you have a modern thermostat Is the bypass hose blocked totally with a plug? Is there a 1/4" (6mm) to 5/16" (8mm ) bleed hole through it? It needs a bleed hole to get the air from the pump up to the thermostat housing. Cheers Peter W Quote Link to post Share on other sites
JJC Posted June 12, 2020 Author Report Share Posted June 12, 2020 I haven’t retorqued the head yet, because of the overheating problem it hasn’t done any miles. The thermostat has the bleed hole, but no mods to bypass hose, no plug. But it all worked fine for several years whilst the FO8 seals were busy rusting away. Didn’t do anything to the head when putting Fo8s in properly just put it all back because it was ok before and had only a few years use after rebuild. It didn’t overheat before with same thermostat and pump. Reason I took the pump off to check it was because running it in the garage the top of the rad was hot but the bottom not so hot. Thermostat and pump both test ok. Put it back together and try again? JJC Quote Link to post Share on other sites
Z320 Posted June 12, 2020 Report Share Posted June 12, 2020 Does only the gauge show you overheating? Or does the engine boil an throw boiling water and steam out? Or what else happens? Top of the rad hot and bottom not so hot is exactly the thing you want from a radiator - so why do you worry? Quote Link to post Share on other sites
JJC Posted June 13, 2020 Author Report Share Posted June 13, 2020 7 hours ago, Z320 said: Does only the gauge show you overheating? Or does the engine boil an throw boiling water and steam out? Or what else happens? Top of the rad hot and bottom not so hot is exactly the thing you want from a radiator - so why do you worry? Gauge runs at 185 then rapidly climbs to maximum. Engine then runs very badly, then stops given half a chance. JJC Quote Link to post Share on other sites
trchris Posted June 13, 2020 Report Share Posted June 13, 2020 Hi Have you tried removing the heater hose from the valve connect a filler hose to the valve and fill the top of the head that way ? Chris Quote Link to post Share on other sites
rcreweread Posted June 13, 2020 Report Share Posted June 13, 2020 Maybe sludge from the water jacket got dislodged when you were doing the figure of eight seals and is now partially blocking the rad - you could try reverse flushing the rad t0 see if that makes any difference and whilst you are at it, you might as well use a cleaning/descaling agent. Cheers Rich Quote Link to post Share on other sites
little jim Posted June 13, 2020 Report Share Posted June 13, 2020 Rich's suggestion sounds good. Dunno if you got rid of all the water jacket 'crud' when you did the FO8s, mine was full of crud back near the drain tap area. Quote Link to post Share on other sites
JJC Posted June 13, 2020 Author Report Share Posted June 13, 2020 Yes the engine is clean internally. I’ll put it back together and try and fill with no air and deal with middle hose and see what happens. Really annoying because whilst the FO8 seals were rusting away it ran just fine! JJC Quote Link to post Share on other sites
roy53 Posted June 13, 2020 Report Share Posted June 13, 2020 At those temps the rad should not be cold at the middle / bottom. For mine it was the rad Quote Link to post Share on other sites
BlueTR3A-5EKT Posted June 13, 2020 Report Share Posted June 13, 2020 5 hours ago, trchris said: Hi Have you tried removing the heater hose from the valve connect a filler hose to the valve and fill the top of the head that way ? Chris +1 That is another method I use when refilling from drained. I run the cold unpressurised (rad cap off) engine with that hose disconnected for a short while to spill out any air. I also have a bleed valve in the back of the thermostat housing. Last year in a rush I forgot to vent the cooling system and the car boiled inside of 15 minutes on the road. Peter W Quote Link to post Share on other sites
stillp Posted June 13, 2020 Report Share Posted June 13, 2020 JJC, if you turn the heater on does it blow warm air? Pete Quote Link to post Share on other sites
JJC Posted June 13, 2020 Author Report Share Posted June 13, 2020 I should be so lucky to test the heater! Will try and get it back together and fill up via the heater valve, squeeze the middle tube, cross fingers and see what happens. JJC Quote Link to post Share on other sites
stillp Posted June 13, 2020 Report Share Posted June 13, 2020 'Bouncing' the car will sometimes help to shift a stubborn air bubble. TRy that while you're at it. Pete Quote Link to post Share on other sites
Nobbyc Posted June 13, 2020 Report Share Posted June 13, 2020 Thermostat faulty and not opening all the way. See what happens without thermostat installed. Quote Link to post Share on other sites
Graham Harris Posted June 14, 2020 Report Share Posted June 14, 2020 Is it pumping large amounts of water out the overflow, could be a blown head gasket , I would do the re torque first and see if that fixes the problem. Graham Quote Link to post Share on other sites
rvwp Posted June 19, 2020 Report Share Posted June 19, 2020 My understanding of the TR4 cooling system is that the bypass system, peculiar to the TR4/4A, is to allows the engine to quickly reach temperature by allowing the water to circulate around the engine only with the thermostat closed. Once operating temperature is reached, the original ' BELLOWS TYPE thermostat opens to allow the water to flow through the radiator, but also closes off the bypass, and permits full flow through the radiator. If a non bellows cheap thermostat is used, without blocking off the bypass with a plug with a bleed hole in it, then water will STILL FLOW through the bypass system once the this style of thermostat opens, and the water will overheat and the engine will get too hot. The original style bellows are I believe still available but expensive, £85, but is the way the system was designed! Running the engine without a thermostat with the bypass still open will only reduce the time the engine reaches operating temperature, not cure overheating. Suggest check which thermostat is fitted and check if bypass is plugged if non bellows type is being used. Rich Quote Link to post Share on other sites
Lebro Posted June 19, 2020 Report Share Posted June 19, 2020 Not peculiar to 4 / 4A, same is true for all the 4 pot engines. Bellows type thermostats can be found for a lot less than the figure you quote at autojumbles, ebay etc. The partial blocking of the bypass circuit seems to be a popular alternative however. Bob. Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.