470 Overheat

[dan4836]

I tried just about everything...

My boat runs great except a very slow heat up after 3200 RPMs until boil over.

I replaced:

1) Thermostat
2) Water pump and housing (twice to be sure)
3) Removed the 3" heat exchanger and replaced with 4"
4) Flushed out the seawater circuit
5) Removed the riser and flushed and cleaned

I installed a new 160 degree thermostat. For some reason, my temp will stay at 120 at rest and increase past 200 very slowly at 3200 rpms

Can the thermostat be installed up side down? I have the springs facing down. One forum I read states the sealoc manual shows this install incorrect.

My only other option is head gasket?

Any thoughts?

[spareparts]

do a compression test and look closely at the plugs, find the one that looks brand new. make sure you don't have old impeller pieces stuck in the power steering cooler

[dan4836]

I don't have power steering and I removed the voltage regulator as I have the upgrade alternator kit. My seawater circuit is very streamline and I back-flushed the circuit.

It has to be a head gasket or riser? My mechanic told me you sometimes can't tell if the riser is bad just by running water through it.

[bradford]

I've had a brand new thermostat not open up fully causing an engine to run slightly hotter. Replaced it and everything was good to go.

[spareparts]

what brand of water pump did you use, I've been burned before using aftermarket pumps. you can plumb in a garden hose y valve between the heat exchanger and the riser, run another hose off the y valve to dump overboard, while running, crack the valve leading to the over board discharge, if the temp starts going down, you have a restricted riser. Be careful, don't starve the exhaust of water or you'll burn the hose

[dan4836]

I used Mercruiser parts.

On the muffs, I can't get the temp gauge over 120.

In the water, temp gauge will stay at 120 at idle.

At 2800 RPMs, I can run all day around 170 degrees.

As soon as I bump the throttle to 3200, the temp will slowly rise to 200.

If I open it up, it will quickly jump past 200 and boil.

My recovery tank makes all kinds of noise...I am not sure if it's air or boiling coolant?

If it's air, then I know it's the head gasket.

My research tells me you can't find a small leak with a compression test because it's not enough pressure at low RPM's to find. Also, a leak down test may not work either.

I don't want to pull the head and find it's something else.

I do notice the riser gets hot as well as the heat exchanger. This still points to seawater not flowing fast enough?

[spareparts]

It should be running hotter than 120 at idle and lower rpm. It sounds like a thermostat issue

[dan4836]

Does anybody know which way the thermostat drops in?

I have the older 470 with iron manifolds. I installed the thermostat with the springs down.

If the thermostat is upside down, I am assuming it will cause a high speed overheat.

Thanks for your help...

[Destroyer]

The spring should be facing the heated water.

A simple test to see if your t-stat is working properly: Take your stat and put it into a saucepan full of water. Bring the water to a boil. Remove the stat with a pair of tongs and look at it. Make sure it's fully open. Then, put a piece of string into the opening that occurred when the spring retracted due to the heat. Let the stat cool and capture the string. Then place the stat, suspended by the string, back into new, cool water and bring it to a boil again. Using a candy thermometer, measure the temp of the water as it's heating up. When the spring opens and the stat drops off the string look at the thermometer reading. That will tell you exactly what temp your stat is opening at. Check it against the reading stamped on the stat housing to see if it's within specs.

[dan4836]

Then that tells me my thermostat is installed upside down.

The heated water is on top from the engine - the spring should face up in that case.

Another thread showed the exact same thing. When the person fliped the t stat, everything ran great.

[bradford]

Any luck with flipping the t stat??

[aussie]

my advice would be remove thermostat and try it see if it over heats

A easy way to check for a head gasket leak or cracked head

(1) you need 4 long screwdrivers
(2) connect hose to engine and run it till its hot
(3) remove all 4 spark plugs
(4) place a screw driver down each spark plug hole
(5) wait a minute remove a screw driver one at a time and check for moisture of the screw driver
(6) if you find one with moisture that's the cylinder that's leaking

I have been using this method since I have been in the trade it works

[dan4836]

I already pulled the head off and took it to a machine shop. He showed me the area he thinks the head gasket was leaking and he thinks it is causing the overheat.

I will be putting everything back together later this week and test rid is scheduled for Sunday...I will keep you posted.

[aussie]

I think most guys on here recommend using a genuine head gasket

[spareparts]

I don't think the Ford gasket will work on the 3.7, it doesn't seal the open deck.

[jaysea]

is your exhaust riser closed up with rust scale ,ive been running a 470 for years ,never had a over heating problem, but changed the hole exhaust system a few years back

[aussie]

I don't think the Ford gasket will work on the 3.7, it doesn't seal the open deck.
thanks SPARES for clearing that up

[dan4836]

I am installing the machined head tomorrow...machine shop said it was warped. Also, installing new riser. Between these two items, overheat issue should be resolved.

I will let you guys know after test run on Sunday.

[aussie]

Has your engine got flat top pistons or dished ones

[dan4836]

Dished pistons

[aussie]

Dished pistons that's strange mine were dished top but some of the other engines I seen on ebay were flat tops were the oversize and did you get it going

[dan4836]

I did get the boat going and we went for a test ride yesterday.

Motor ran great but i still get a large gap between temp readings. If I let the boat idle, the temp will read 120. If I cruise the boat at 3500 rpm, the temp will slowly get to 200. Back off the throttle to 1200 and the temp will drop down to 120.

I did not overheat but I did get coolant releasing into the overflow container.

My question - If I have a 160 degree thermostat, why a 80 degree sway in temp?

Items I changed so far:

1) Upgraded from 3" to 4" heat exchanger. Checked and cleaned exchanger.

2) Replaced the raw water pump three times. The last time replaced the housing as well.

3) Replaced the riser.

4) Removed the water cooled voltage regulator and ran a new hose from the transom to the heat exchanger

5) Removed the head, machined and re-installed

6) New thermostat

What else is left?

My only thoughts now are something in the flow of coolant on the fresh water side. Either the thermostat or the engine circulating pump. I installed the thermostat with the springs down ( I have the old stye 470) perhaps I have the incorrect thermostat?

Any thoughts?

[aussie]

It has to be water flow . raw water may not be flowing enough . Water pump on engine not pumping enough . Did you check the water pump impellor on the engine there is a cover on the timing cover check if the impellor is worn . I don't know how you are checking your leg pump most guys use the ear muffs on the legs and its not a good way to check your pump as its being feed under pressure when I have heating problem I run the leg in a drum so you get to see how well the pump is working

Find the hose that comes of your leg and connect a garden water hose to it and turn it on . Follow the route of the hoses and remove one hose at a time to see if something is restricting water ( example ; check water flow before manifold and after ) you need to eliminate everything that water goes through. If everything is flowing good then check your raw water pump . Put the leg in a drum leave the hose of the leg start the engine and see how much water the pump is pumping .If all is fine then its your water system on the engine

It can only be the water pump on your engine . you have done every thing else

Spares might be able to help you more as car mechanic hes a boat one

GOOD LUCK :clap:

[dan4836]

After looking closely at my thermostat and housing, I found the thermostat installed does not close off the circuit (engine side). I have the older style manifolds and the bottom part of the thermostat is smaller than the hole that allows the coolant to flow back through the engine.

In other words, when the thermostat is closed, no water can go to the heat exchanger. when the thermostat opens, on top the coolant can flow from the bottom and through the thermostat to complete the circuit to the heat exchanger. Also, when the thermostat opens, it should close off the circuit that goes back through the engine.

- The thermostat foot is too small and does not make it to the bottom to close of the hole.

My research shows that only two thermostats are made for the 470. One for my style manifold and the other for the aluminum manifold set up.

Any suggestions?

[aussie]

Take. The thermostat out and try it. Even with the thermostat not being rite once it opens it shouldn't overheat

[dan4836]

If I take out the thermostat, the coolant will go where it wants. Some will go to the exchanger and some will go back through the engine.

[macojoe]

Make sure the T stats are in the right way! I have seen people put some in backwards and they can't work right! Can't do it with all but some you can, worth a try.
Are you sure the T stas are opening?? take out and put in boiling water see if they open and close when they get cool? Might need new ones?
Motor water pump, mine had the impeller rot off it and could not move the water, someone had put a auto water pump on it.

[dan4836]

I had a marine mechanic come over to take a look and this is what we found.

The thermostat that is installed does not look correct and I was to purchase another thermostat for the 470 that looks like it will do its job. The new thermostat part numbers match up with the newer, aluminum manifolds.

From what we see, the part number of the thermostat installed is the correct part number but it does not look like it will redirect the coolant to the heat exchanger.

The mechanic said my setup is unusual because the thermostat does more than one function. It lets water go to the heat exchanger and closes the hole the goes back to the engine.

I will see on Saturday during a test ride...

[dan4836]

Found my problem! After replacing just about everything, I found my thermostat is incorrect.

I researched this for weeks and found the thermostat my engine calls for matches to a Mercruiser part number that is incorrect. I put the thermostat for the newer, aluminum type manifold in my older cast iron type (first generation 470) and it worked perfect. 170 degrees at 4000 RPMs for ten minutes.

I wonder how many other people are using the incorrect thermostat in their 470 based on Mercruiser's numbers.

Now I can post about other restoration projects and maybe show some fish pictures this year!

[aussie]

Glad you found the problem will have to make sure I use the correct one Hey spares no input from you on this one

[smokeonthewater]

Spare has family things to deal with right now

[cfelton]

Glad you figured out what your problem was. My 170 heats up alittle when I run it really hard, makes me wonder if I might have a similar problem. If you can take some pictures of the thermostat you removed and the part numbers for both thermostats.

[aussie]

Spare has family things to deal with right now
Hope things are OK with him

[Destroyer]

Hope things are OK with him

Aussie, I know you can only read and post from your phone right now, so you probably can't get to look in the "Off Topic" section. His mom died yesterday, so he will not be available for a while.

[aussie]

Man I'm sorry to hear of his loss thanks for informing me

[smokeonthewater]

I'm sorry, I didn't realize you couldn't find the thread.... It's in the last few posts of this one.

http://www.wellcraftv20.com/community/showthread.php?p=208375#post208375